ORCID Profile
0000-0001-5958-7457
Current Organisation
University of Wollongong
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Medical physics | Particle physics | Other Physical Sciences | Medical Devices | Space instrumentation | Biomedical Engineering | Synchrotrons; Accelerators; Instruments and Techniques | Medical Physics | Particle and high energy physics | Atomic and Molecular Physics |
Medical Instruments | Expanding Knowledge in the Physical Sciences | Scientific Instruments | Cancer and Related Disorders |
Publisher: Wiley
Date: 15-03-2013
DOI: 10.1118/1.4794487
Abstract: The conformity of the achieved dose distribution to the treatment plan strongly correlates with the accuracy of seed implantation in a prostate brachytherapy treatment procedure. Incorrect seed placement leads to both short and long term complications, including urethral and rectal toxicity. The authors present BrachyView, a novel concept of a fast intraoperative treatment planning system, to provide real-time seed placement information based on in-body gamma camera data. BrachyView combines the high spatial resolution of a pixellated silicon detector (Medipix2) with the volumetric information acquired by a transrectal ultrasound (TRUS). The two systems will be embedded in the same probe so as to provide anatomically correct seed positions for intraoperative planning and postimplant dosimetry. Dosimetric calculations are based on the TG-43 method using the real position of the seeds. The purpose of this paper is to demonstrate the feasibility of BrachyView using the Medipix2 pixel detector and a pinhole collimator to reconstruct the real-time 3D position of low dose-rate brachytherapy seeds in a phantom. BrachyView incorporates three Medipix2 detectors coupled to a multipinhole collimator. Three-dimensionally triangulated seed positions from multiple planar images are used to determine the seed placement in a PMMA prostate phantom in real time. MATLAB codes were used to test the reconstruction method and to optimize the device geometry. The results presented in this paper show a 3D position reconstruction accuracy of the seed in the range of 0.5-3 mm for a 10-60 mm seed-to-detector distance interval (Z direction), respectively. The BrachyView system also demonstrates a spatial resolution of 0.25 mm in the XY plane for sources at 10 mm distance from Medipix2 detector plane, comparable to the theoretical value calculated for an equivalent gamma camera arrangement. The authors successfully demonstrated the capability of BrachyView for real-time imaging (using a 3 s data acquisition time) of different brachytherapy seed configurations (with an activity of 0.05 U) throughout a 60 × 60 × 60 mm(3) Perspex prostate phantom. The newly developed miniature gamma camera component of BrachyView, with its high spatial resolution and real time capability, allows accurate 3D localization of seeds in a prostate phantom. Combination of the gamma camera with TRUS in a single probe will complete the BrachyView system.
Publisher: MDPI AG
Date: 20-10-2022
Abstract: High dose rate radiotherapies such as FLASH and microbeam radiotherapy (MRT) both have developed to the stage of first veterinary studies within the last decade. With the development of a new research tool for high dose rate radiotherapy at the end station P61A of the synchrotron beamline P61 on the DESY c us in Hamburg, we increased the research capacity in this field to speed up the translation of the radiotherapy techniques which are still experimental, from bench to bedside. At P61, dose rates of several hundred Gy/s can be delivered. Compared to dedicated biomedical beamlines, the beam width available for MRT experiments is a very restrictive factor. We developed two model systems specifically to suit these specific technical parameters and tested them in a first set of experiments.
Publisher: Elsevier BV
Date: 12-2011
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2020
Publisher: IOP Publishing
Date: 26-06-2013
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2020
Publisher: Wiley
Date: 04-11-2020
DOI: 10.1002/MP.13871
Abstract: To report on experimental results of a high spatial resolution silicon-based detector exposed to therapeutic quality proton beams in a 0.95 T transverse magnetic field. These experimental results are important for the development of accurate and novel dosimetry methods in future potential real-time MRI-guided proton therapy systems. A permanent magnet device was utilized to generate a 0.95 T magnetic field over a 4 × 20 × 15 cm The nominal Bragg peak for each proton energy was successfully observed with a 0.2 mm spatial resolution in the 0.95 T transverse magnetic field in both a depth and lateral profiles. The proton beam deflection (at 0.95 T) was a consistent 2 ±0.5 mm at the center of the magnetic volume for each beam energy. However, a pristine Bragg peak was not observed for each energy. This was caused by the detector packaging having small air gaps between layers of the phantom material surrounding the diode array. These air gaps act to degrade the shape of the Bragg peak, and further to this, the nonwater equivalent silicon chip acts to separate the Bragg peak into multiple peaks depending on the proton path taken. Overall, a promising performance of the silicon detector array was observed, however, with a qualitative assessment rather than a robust quantitative dosimetric evaluation at this stage of development. For the first time, a high-resolution silicon-based radiation detector has been used to measure proton beam Bragg peak deflections in a phantom due to a strong magnetic field. Future efforts are required to optimize the detector packaging to strengthen the robustness of the dosimetric quantities obtained from the detector. Such high-resolution silicon diode arrays may be useful in future efforts in MRI-guided proton therapy research.
Publisher: Wiley
Date: 22-05-2020
DOI: 10.1002/ACM2.12906
Publisher: Wiley
Date: 22-05-2018
DOI: 10.1002/ACM2.12345
Publisher: IEEE
Date: 10-2016
Publisher: International Union of Crystallography (IUCr)
Date: 09-02-2021
DOI: 10.1107/S1600577520016811
Abstract: Microbeam radiation therapy (MRT) is a developing radiotherapy, based on the use of beams only a few tens of micrometres wide, generated by synchrotron X-ray sources. The spatial fractionation of the homogeneous beam into an array of microbeams is possible using a multislit collimator (MSC), i.e. a machined metal block with regular apertures. Dosimetry in MRT is challenging and previous works still show differences between calculated and experimental dose profiles of 10–30%, which are not acceptable for a clinical implementation of treatment. The interaction of the X-rays with the MSC may contribute to the observed discrepancies the present study therefore investigates the dose contribution due to radiation interaction with the MSC inner walls and radiation leakage of the MSC. Dose distributions inside a water-equivalent phantom were evaluated for different field sizes and three typical spectra used for MRT studies at the European Synchrotron Biomedical beamline ID17. Film dosimetry was utilized to determine the contribution of radiation interaction with the MSC inner walls Monte Carlo simulations were implemented to calculate the radiation leakage contribution. Both factors turned out to be relevant for the dose deposition, especially for small fields. Photons interacting with the MSC walls may bring up to 16% more dose in the valley regions, between the microbeams. Depending on the chosen spectrum, the radiation leakage close to the phantom surface can contribute up to 50% of the valley dose for a 5 mm × 5 mm field. The current study underlines that a detailed characterization of the MSC must be performed systematically and accurate MRT dosimetry protocols must include the contribution of radiation leakage and radiation interaction with the MSC in order to avoid significant errors in the dose evaluation at the micrometric scale.
Publisher: International Union of Crystallography (IUCr)
Date: 26-07-2016
DOI: 10.1107/S1600577516009322
Abstract: Microbeam radiation therapy (MRT) is a novel irradiation technique for brain tumours treatment currently under development at the European Synchrotron Radiation Facility in Grenoble, France. The technique is based on the spatial fractionation of a highly brilliant synchrotron X-ray beam into an array of microbeams using a multi-slit collimator (MSC). After promising pre-clinical results, veterinary trials have recently commenced requiring the need for dedicated quality assurance (QA) procedures. The quality of MRT treatment demands reproducible and precise spatial fractionation of the incoming synchrotron beam. The intensity profile of the microbeams must also be quickly and quantitatively characterized prior to each treatment for comparison with that used for input to the dose-planning calculations. The Centre for Medical Radiation Physics (University of Wollongong, Australia) has developed an X-ray treatment monitoring system (X-Tream) which incorporates a high-spatial-resolution silicon strip detector (SSD) specifically designed for MRT. In-air measurements of the horizontal profile of the intrinsic microbeam X-ray field in order to determine the relative intensity of each microbeam are presented, and the alignment of the MSC is also assessed. The results show that the SSD is able to resolve in idual microbeams which therefore provides invaluable QA of the horizontal field size and microbeam number and shape. They also demonstrate that the SSD used in the X-Tream system is very sensitive to any small misalignment of the MSC. In order to allow as rapid QA as possible, a fast alignment procedure of the SSD based on X-ray imaging with a low-intensity low-energy beam has been developed and is presented in this publication.
Publisher: Elsevier BV
Date: 08-2013
Publisher: MDPI AG
Date: 08-10-2021
DOI: 10.3390/INSTRUMENTS5040032
Abstract: Hydrogenated amorphous silicon (a-Si:H) can be produced by plasma-enhanced chemical vapor deposition (PECVD) of SiH4 (silane) mixed with hydrogen. The resulting material shows outstanding radiation hardness properties and can be deposited on a wide variety of substrates. Devices employing a-Si:H technologies have been used to detect many different kinds of radiation, namely, minimum ionizing particles (MIPs), X-rays, neutrons, and ions, as well as low-energy protons and alphas. However, the detection of MIPs using planar a-Si:H diodes has proven difficult due to their unsatisfactory S/N ratio arising from a combination of high leakage current, high capacitance, and limited charge collection efficiency (50% at best for a 30 µm planar diode). To overcome these limitations, the 3D-SiAm collaboration proposes employing a 3D detector geometry. The use of vertical electrodes allows for a small collection distance to be maintained while preserving a large detector thickness for charge generation. The depletion voltage in this configuration can be kept below 400 V with a consequent reduction in the leakage current. In this paper, following a detailed description of the fabrication process, the results of the tests performed on the planar p-i-n structures made with ion implantation of the dopants and with carrier selective contacts are illustrated.
Publisher: Elsevier BV
Date: 07-2005
Publisher: Frontiers Media SA
Date: 08-05-2020
Publisher: IOP Publishing
Date: 21-06-2018
Publisher: AIP
Date: 2010
DOI: 10.1063/1.3478205
Publisher: Elsevier BV
Date: 12-2011
Publisher: IOP Publishing
Date: 31-07-2012
Publisher: IEEE
Date: 10-2013
Publisher: MDPI AG
Date: 30-12-2022
DOI: 10.3390/APP12010328
Abstract: The Centre for Medical Radiation Physics introduced the concept of Silicon On Insulator (SOI) microdosimeters with 3-Dimensional (3D) cylindrical sensitive volumes (SVs) mimicking the dimensions of cells in an array. Several designs of high-definition 3D SVs fabricated using 3D MEMS technology were implemented. 3D SVs were fabricated in different sizes and configurations with diameters between 18 and 30 µm, thicknesses of 2–50 µm and at a pitch of 50 µm in matrices with volumes of 20 × 20 and 50 × 50. SVs were segmented into sub-arrays to reduce capacitance and avoid pile up in high-dose rate pencil beam scanning applications. Detailed TCAD simulations and charge collection studies in in idual SVs have been performed. The microdosimetry probe (MicroPlus) is composed of the silicon microdosimeter and low-noise front–end readout electronics housed in a PMMA waterproof sheath that allows measurements of lineal energies as low as 0.4 keV/µm in water or PMMA. Microdosimetric quantities measured with SOI microdosimeters and the MicroPlus probe were used to evaluate the relative biological effectiveness (RBE) of heavy ions and protons delivered by pencil-beam scanning and passive scattering systems in different particle therapy centres. The 3D detectors and MicroPlus probe developed for microdosimetry have the potential to provide confidence in the delivery of RBE optimized particle therapy when introduced into routine clinical practice.
Publisher: IEEE
Date: 10-2011
Publisher: IOP Publishing
Date: 16-11-2015
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2023
Publisher: Wiley
Date: 17-04-2017
DOI: 10.1002/MP.12209
Abstract: A high resolution, water equivalent, optical and passive x-ray dosimeter has been constructed using plastic scintillator and optical fiber. This dosimeter has a peak edge-on spatial resolution of 100 μm in one dimension, with a 10 μm resolution dosimeter under investigation. The dosimeter design has a potential application in synchrotron x-ray microbeam radiation therapy where a high resolution is vital for accurate dose measurements and quality assurance. BC-400 plastic scintillator, of thickness 100 μm, was optically coupled to an optical fiber with core diameter 1 mm. The end was coated in optical paint to improve sensitivity. An identical fiber was made without the scintillator to measure the background Cherenkov radiation induced in the fiber, to allow background signal subtraction. The light captured by the fibers was measured by PMTs. The probe system was exposed to a 6 MV, 10 × 10 cm The measured profiles matched well with ionisation chamber data. Important beam parameters such as penumbra width and percent depth dose at various depths matched the ionisation chamber data, within uncertainty. This work demonstrates that high resolutions can be achieved with a scintillation and optical fiber system. The probe is water-equivalent, passive, energy independent, radiation hard and inexpensive, making it ideal for further improvements for use with microbeam radiation therapy.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2013
Publisher: Wiley
Date: 19-11-2020
DOI: 10.1002/MP.13899
Abstract: Microbeam radiation therapy (MRT) is an emerging radiation oncology modality ideal for treating inoperable brain tumors. MRT employs quasi-parallel beams of low-energy x rays produced from modern synchrotrons. A tungsten carbide multislit collimator (MSC) spatially fractionates the broad beam into rectangular beams. In this study, the MSC creates beams 50 μm wide ("peaks") separated by a center-to-center distance of 400 μm ("valleys"). The peak to valley dose ratio (PVDR) is of critical importance to the efficacy of MRT. The underlying radiobiological advantage of MRT relies on high peak dose for tumor control and low valley dose for healthy tissue sparing. Cardio synchronous brain motion of the order 100-200 μm is comparable to microbeam width and spacing. The motion can have a detrimental effect on the PVDR, full width at half maximum (FWHM) of the microbeams, and ultimately the dose distribution. We present the first experimental measurement of the effect of brain motion on MRT dose distribution. Dosimetry in MRT is difficult due to the high dose rate (up to 15-20 kGy/s) and small field sizes. A real-time dosimetry system based on a single silicon strip detector (SSSD) has been developed with spatial resolution ~10 μm. The SSSD was placed in a water-equivalent phantom and scanned through the microbeam distribution. A monodirectional positioning stage reproduced brain motion during the acquisition. Microbeam profiles were reconstructed from the SSSD and compared with Geant4 simulation and radiochromic HD-V2 film. The SSSD is able to reconstruct dose profiles within 2 μm compared to film. When brain motion is applied the SSSD shows a two time increase in FWHM of profiles and 50% reduction in PVDR. This is confirmed by Geant4 and film data. Motion-induced misalignment and distortion of microbeams at treatment delivery will result in a reduced PVDR and increased irradiation of additional healthy tissue compromising the radiobiological effectiveness of MRT. The SSSD was able to reconstruct dose profiles under motion conditions and predict similar effects on FWHM and PVDR as by the simulation. The SSSD is a simple to setup, real-time detector which can provide time-resolved high spatial resolution dosimetry of microbeams in MRT.
Publisher: Wiley
Date: 09-10-2017
DOI: 10.1002/MP.12563
Abstract: This work aims to characterize a proton pencil beam scanning (PBS) and passive double scattering (DS) systems as well as to measure parameters relevant to the relative biological effectiveness (RBE) of the beam using a silicon on insulator (SOI) microdosimeter with well-defined 3D sensitive volumes (SV). The dose equivalent downstream and laterally outside of a clinical PBS treatment field was assessed and compared to that of a DS beam. A novel silicon microdosimeter with well-defined 3D SVs was used in this study. It was connected to low noise electronics, allowing for detection of lineal energies as low as 0.15 keV/μm. The microdosimeter was placed at various depths in a water phantom along the central axis of the proton beam, and at the distal part of the spread-out Bragg peak (SOBP) in 0.5 mm increments. The RBE values of the pristine Bragg peak (BP) and SOBP were derived using the measured microdosimetric lineal energy spectra as inputs to the modified microdosimetric kinetic model (MKM). Geant4 simulations were performed in order to verify the calculated depth-dose distribution from the treatment planning system (TPS) and to compare the simulated dose-mean lineal energy to the experimental results. For a 131 MeV PBS spot (124.6 mm R The SOI microdosimeter with its well-defined 3D SV has applicability in characterizing proton radiation fields and can measure relevant physical parameters to model the RBE with submillimeter spatial resolution. It has been shown that for a physical dose of 1.82 Gy at the BP, the derived RBE based on the MKM model increased from 1.14 to 1.6 in the BP and its distal part. Good agreement was observed between the experimental and simulation results, confirming the potential application of SOI microdosimeter with 3D SV for quality assurance in proton therapy.
Publisher: IOP Publishing
Date: 13-02-2020
Abstract: Microdosimetry is a particularly powerful method to estimate the relative biological effectiveness (RBE) of any mixed radiation field. This is particularly convenient for therapeutic heavy ion therapy (HIT) beams, referring to ions larger than protons, where the RBE of the beam can vary significantly along the Bragg curve. Additionally, due to the sharp dose gradients at the end of the Bragg peak (BP), or spread out BP, to make accurate measurements and estimations of the biological properties of a beam a high spatial resolution is required, less than a millimetre. This requirement makes silicon microdosimetry particularly attractive due to the thicknesses of the sensitive volumes commonly being ∼10 [Formula: see text]m or less. Monte Carlo (MC) codes are widely used to study the complex mixed HIT radiation field as well as to model the response of novel microdosimeter detectors when irradiated with HIT beams. Therefore it is essential to validate MC codes against experimental measurements. This work compares measurements performed with a silicon microdosimeter in mono-energetic [Formula: see text], [Formula: see text] and [Formula: see text] ion beams of therapeutic energies, against simulation results calculated with the Geant4 toolkit. Experimental and simulation results were compared in terms of microdosimetric spectra (dose lineal energy, [Formula: see text]), the dose mean lineal energy, y
Publisher: IOP Publishing
Date: 03-2022
DOI: 10.1088/1748-0221/17/03/C03033
Abstract: Hydrogenated Amorphous Silicon (a-Si:H) is a well known material for its intrinsic radiation hardness and is primarily utilized in solar cells as well as for particle detection and dosimetry. Planar p-i-n diode detectors are fabricated entirely by means of intrinsic and doped PECVD of a mixture of Silane (SiH 4 ) and molecular hydrogen. In order to develop 3D detector geometries using a-Si:H, two options for the junction fabrication have been considered: ion implantation and charge selective contacts through atomic layer deposition. In order to test the functionality of the charge selective contact electrodes, planar detectors have been fabricated utilizing this technique. In this paper, we provide a general overview of the 3D fabrication project followed by the results of leakage current measurements and X-ray dosimetric tests performed on planar diodes containing charge selective contacts to investigate the feasibility of the charge selective contact methodology for integration with the proposed 3D detector architectures.
Publisher: Elsevier BV
Date: 09-2021
Publisher: IOP Publishing
Date: 31-08-2020
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 05-2021
Publisher: IOP Publishing
Date: 25-02-0033
Publisher: Elsevier BV
Date: 03-2019
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2018
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2014
Publisher: AIP Publishing
Date: 28-06-2021
DOI: 10.1063/5.0040013
Abstract: Recommendations for an experimental protocol for beam alignment/optimization and dosimetry relating to in vitro studies at the Imaging and Medical Beam Line of the Australian Synchrotron are presented. An evaluation of the protocol, based upon the consistency and reproducibility of in vitro experiments performed over several years at the Australian Synchrotron, is provided for the community.
Publisher: Elsevier BV
Date: 04-2020
Publisher: Wiley
Date: 03-2016
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2020
Publisher: IOP Publishing
Date: 30-10-2019
Publisher: AIP Publishing
Date: 02-01-2017
DOI: 10.1063/1.4973628
Abstract: A diamond based microdosimeter prototype featuring a 3D lateral electrode structure was created using laser ablation and active brazing alloys and characterised by means of ion beam induced charge collection measurements and finite element analysis, using Synopsys TCAD simulation package.
Publisher: Elsevier BV
Date: 12-2011
Publisher: Elsevier BV
Date: 04-2018
Publisher: Frontiers Media SA
Date: 13-03-2020
Publisher: IOP Publishing
Date: 05-04-2019
Abstract: A prototype in-body gamma camera system with integrated trans-rectal ultrasound (TRUS) and associated real-time image acquisition and analysis software was developed for intraoperative source tracking in high dose rate (HDR) brachytherapy. The accuracy and temporal resolution of the system was validated experimentally using a deformable tissue-equivalent prostate gel phantom and a full clinical HDR treatment plan. The BrachyView system was able to measure 78% of the 200 source positions with an accuracy of better than 1 mm. A minimum acquisition time of 0.28 s/frame was required to achieve this accuracy, restricting dwell times to a minimum of 0.3 s. Additionally, the performance of the BrachyView-TRUS fusion probe for mapping the spatial location of the tracked source within the prostate volume was evaluated. A global coordinate system was defined by scanning the phantom with the probe in situ using a CT scanner, and was subsequently used for co-registration of the BrachyView and TRUS fields of view (FoVs). TRUS imaging was used to segment the prostate volume and reconstruct it into a three-dimensional (3D) image. Fusion of the estimated source locations with the 3D prostate image was performed using integrated 3D visualisation software. HDR BrachyView is demonstrated to be a valuable tool for intraoperative source tracking in HDR brachytherapy, capable of resolving source dwell locations relative to the prostate anatomy when combined with TRUS.
Publisher: IOP Publishing
Date: 2019
Publisher: IEEE
Date: 10-2009
Publisher: Elsevier BV
Date: 2014
DOI: 10.1016/J.APRADISO.2013.06.001
Abstract: MOSkin detectors were studied to perform real-time in vivo dose measurements in high dose rate prostate brachytherapy. Measurements were performed inside an urethral catheter in a gel phantom simulating a real prostate implant. Measured and expected doses were compared and the discrepancy was found to be within 8.9% and 3.8% for single MOSkin and dual-MOSkin configurations, respectively. Results show that dual-MOSkin detectors can be profitably adopted in prostate brachytherapy treatments to perform real-time in vivo dosimetry inside the urethra.
Publisher: Wiley
Date: 12-08-2017
DOI: 10.1002/MP.12469
Abstract: The aim of in vivo skin dosimetry was to measure the absorbed dose to the skin during radiotherapy, when treatment planning calculations cannot be relied on. It is of particularly importance in hypo-fractionated stereotactic modalities, where excessive dose can lead to severe skin toxicity. Currently, commercial diodes for such applications are with water equivalent depths ranging from 0.5 to 0.8 mm. In this study, we investigate a new detector for skin dosimetry based on a silicon epitaxial diode, referred to as the skin diode. The skin diode is manufactured on a thin epitaxial layer and packaged using the "drop-in" technology. It was characterized in terms of percentage depth dose, dose linearity, and dose rate dependence, and benchmarked against the Attix ionization chamber. The response of the skin diode in the build-up region of the percentage depth dose (PDD) curve of a 6 MV clinical photon beam was investigated. Geant4 radiation transport simulations were used to model the PDD in order to estimate the water equivalent measurement depth (WED) of the skin diode. Measured output factors using the skin diode were compared with the MOSkin detector and EBT3 film at 10 cm depth and at surface at isocenter of a water equivalent phantom. The intrinsic angular response of the skin diode was also quantified in charge particle equilibrium conditions (CPE) and at the surface of a solid water phantom. Finally, the radiation hardness of the skin diode up to an accumulated dose of 80 kGy using photons from a Co-60 gamma source was evaluated. The PDD curve measured with the skin diode was within 0.5% agreement of the equivalent Geant4 simulated curve. When placed at the phantom surface, the WED of the skin diode was estimated to be 0.075 ± 0.005 mm from Geant4 simulations and was confirmed using the response of a corrected Attix ionization chamber placed at water equivalent depth of 0.075 mm, with the measurement agreement to within 0.3%. The output factor measurements at 10 cm depth were within 2% of those measured with film and the MOSkin detector down to a field size of 2 × 2 cm This work characterizes an innovative detector for in vivo and real-time skin dose measurements that is based on an epitaxial silicon diode combined with the Centre for Medical Radiation Physics (CMRP) "drop-in" packaging technology. The skin diode proved to have a water equivalent depth of measurement of 0.075 ± 0.005 mm and the ability to measure doses accurately relative to reference detectors.
Publisher: Elsevier BV
Date: 09-2017
DOI: 10.1016/J.EJMP.2017.05.003
Abstract: Three MOSkins dosimeters were assembled over a rectal probe and used to perform in vivo dosimetry during HDR brachytherapy treatments of vaginal cancer. The purpose of this study was to verify the applicability of the developed tool to evaluate discrepancies between planned and measured doses to the rectal wall. MOSkin dosimeters from the Centre for Medical Radiation Physics are particularly suitable for brachytherapy procedures for their ability to be easily incorporated into treatment instrumentation. In this study, 26 treatment sessions of HDR vaginal brachytherapy were monitored using three MOSkin mounted on a rectal probe. A total of 78 measurements were collected and compared to doses determined by the treatment planning system. Mean dose discrepancy was determined as 2.2±6.9%, with 44.6% of the measurements within ±5%, 89.2% within ±10% and 10.8% higher than ±10%. When dose discrepancies were grouped according to the time elapsed between imaging and treatment (i.e., group 1: ≤90min group 2: >90min), mean discrepancies resulted in 4.7±3.6% and 7.1±5.0% for groups 1 and 2, respectively. Furthermore, the position of the dosimeter on the rectal catheter was found to affect uncertainty, where highest uncertainties were observed for the dosimeter furthest inside the rectum. This study has verified MOSkin applicability to in-patient dose monitoring in gynecological brachytherapy procedures, demonstrating the dosimetric rectal probe setup as an accurate and convenient IVD instrument for rectal wall dose verification. Furthermore, the study demonstrates that the delivered dose discrepancy may be affected by the duration of treatment planning.
Publisher: International Union of Crystallography (IUCr)
Date: 2022
DOI: 10.1107/S1600577521011140
Abstract: Successful transition of synchrotron-based microbeam radiation therapy (MRT) from pre-clinical animal studies to human trials is dependent upon ensuring that there are sufficient and adequate measures in place for quality assurance purposes. Transmission detectors provide researchers and clinicians with a real-time quality assurance and beam-monitoring instrument to ensure safe and accurate dose delivery. In this work, the effect of transmission detectors of different thicknesses (10 and 375 µm) upon the photon energy spectra and dose deposition of spatially fractionated synchrotron radiation is quantified experimentally and by means of a dedicated Geant4 simulation study. The simulation and experimental results confirm that the presence of the 375 µm thick transmission detector results in an approximately 1–6% decrease in broad-beam and microbeam peak dose. The capability to account for the reduction in dose and change to the peak-to-valley dose ratio justifies the use of transmission detectors as thick as 375 µm in MRT provided that treatment planning systems are able to account for their presence. The simulation and experimental results confirm that the presence of the 10 µm thick transmission detector shows a negligible impact ( .5%) on the photon energy spectra, dose delivery and microbeam structure for both broad-beam and microbeam cases. Whilst the use of 375 µm thick detectors would certainly be appropriate, based upon the idea of best practice the authors recommend that 10 µm thick transmission detectors of this sort be utilized as a real-time quality assurance and beam-monitoring tool during MRT.
Publisher: Wiley
Date: 13-10-2017
DOI: 10.1002/MP.12583
Abstract: Microdosimetry is a vital tool for assessing the microscopic patterns of energy deposition by radiation, which ultimately govern biological effect. Solid-state, silicon-on-insulator microdosimeters offer an approach for making microdosimetric measurements with high spatial resolution (on the order of tens of micrometers). These high-resolution, solid-state microdosimeters may therefore play a useful role in characterizing proton radiotherapy fields, particularly for making highly resolved measurements within the Bragg peak region. In this work, we obtain microdosimetric measurements with a solid-state microdosimeter (MicroPlus probe) in a clinical, spot-scanning proton beam of small spot size. The MicroPlus probe had a 3D single sensitive volume on top of silicon oxide. The sensitive volume had an active cross-sectional area of 250 μm × 10 μm and thickness of 10 μm. The proton facility was a synchrotron-based, spot-scanning system with small spot size (σ ≈ 2 mm). We performed measurements with the clinical beam current (≈1 nA) and had no detected pulse pile-up. Measurements were made in a water-equivalent phantom in water-equivalent depth (WED) increments of 0.25 mm or 1.0 mm along pristine Bragg peaks of energies 71.3 MeV and 159.9 MeV, respectively. For each depth, we measured lineal energy distributions and then calculated the dose-weighted mean lineal energy, y¯D. The measurements were repeated for two field sizes: 4 × 4 cm For both 71.3 MeV and 159.9 MeV and for both field sizes, y¯D increased with depth toward the distal edge of the Bragg peak, a result consistent with Monte Carlo calculations and measurements performed elsewhere. For the 71.3 MeV, 4 × 4 cm We performed microdosimetric measurements with a novel solid-state, silicon-on-insulator microdosimeter in a clinical spot-scanning proton beam of small spot size and unmodified beam current. For all of the proton field sizes and energies considered, the measurements of y¯D were in agreement with expected trends. Furthermore, we obtained measurements with a spatial resolution of 10 μm in the beam direction. This spatial resolution greatly exceeded that possible with a conventional gaseous tissue-equivalent proportional counter and allowed us to perform a high-resolution investigation within the Bragg peak region. The MicroPlus probe is therefore suitable for applications in proton radiotherapy.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-2020
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2014
Publisher: IEEE
Date: 10-2013
Publisher: Elsevier BV
Date: 11-2017
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2019
Publisher: Elsevier BV
Date: 11-2017
Publisher: Wiley
Date: 17-07-2015
DOI: 10.1118/1.4926778
Abstract: In this work, the "edgeless" silicon detector technology is investigated, in combination with an innovative packaging solution, to manufacture silicon detectors with negligible angular response. The new diode is also characterized as a dosimeter for radiotherapy with the aim to verify its suitability as a single detector for in vivo dosimetry as well as large area 2D array that does not require angular correction to their response. For the characterisation of the "edgeless-drop-in" detector technology, a set of s les have been manufactured with different sensitive areas (1 × 1 and 0.5 × 0.5 mm(2)) and different thicknesses (0.1 and 0.5 mm) in four different combinations of top and peripheral p-n junction fabricated on p-type and n-type silicon substrates. The diode probes were tested in terms of percentage depth dose (PDD), dose rate, and linearity and compared to ion chambers. Measurements of the output factor have been compared to film. The angular response of the diodes probes has been tested in a cylindrical PMMA phantom, rotated with bidirectional accuracy of 0.25° under 10 × 10 cm(2) 6 MV Linac photon beam. The radiation hardness has been investigated as well as the effect of radiation damage on the angular and dose rate response of the diode probes when irradiated with photons from a Co-60 gamma source up to dose of 40 kGy. The PDDs measured by the edgeless detectors show an agreement with the data obtained using ion chambers within ±2%. The output factor measured with the smallest area edgeless diodes (0.5 × 0.5 mm(2)-0.1 and 0.5 mm thick) matches EBT3 film to within 2% for square field size from 10 to 0.5 cm side equivalent distance. The dose rate dependence in a dose per pulse range of 0.9 × 10(-5)-2.7 × 10(-4) Gy ulse was less than -7% and +300% for diodes fabricated on p-type and n-type substrates, respectively. The edgeless diodes fabricated on the p-type substrate demonstrated degradation of the response as a function of the irradiation dose within 5%-15%, while diodes on the n-type substrate show a variation of approximately 30% after 40 kGy. The angular response of all probes is minimal (within 2%) but the N on N and P on P configurations show the best performances with an angular dependence of ±1.0% between 0° and 180° in the transversal direction. In this configuration, the space charge region of the passive diode extends from the behind and sidewall toward the anode on the top providing beneficial electric field distribution in the peripheral area of the diode. Such performance has also been tested after irradiation by Co-60 up to 40 kGy with no measurable change in angular response. A new edgeless-drop-in silicon diode fabrication and packaging technology has been used to develop detectors that show no significant angular dependence in their response for dosimetry in radiation therapy. From the characterisation of the diodes, proposed in a wide range of different geometries and configurations, the authors recommend the P-on-P detectors in conjunction with "drop in" packaging technology as the candidate for further development as single diode probe or 2D diode array for dosimetry in radiotherapy.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2016
Publisher: IEEE
Date: 09-2025
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2009
Publisher: IOP Publishing
Date: 2019
Publisher: IOP Publishing
Date: 2019
Publisher: IOP Publishing
Date: 2019
Publisher: IOP Publishing
Date: 2019
Publisher: Wiley
Date: 12-07-2019
DOI: 10.1002/MP.13686
Abstract: Magnetic field effects on dose distribution and detector functionality must be well understood. The detector utilized to investigate these magnetic field effects was the DUO silicon array detector the performance of this high spatial resolution detector was assessed under these conditions. The results were compared to Gafchromic EBT3 film to highlight any intrinsic magnetic field effects in the silicon. The results were also compared to previously published MagicPlate-512 (M512) data. The DUO has an improved spatial resolution (200 µm) over the M512 (2 mm). A permanent magnet named Magnetic Apparatus for RaDiation Oncology Studies (MARDOS) paired with a standard linear accelerator (linac) enables either transverse (1.2 T) or inline (0.95 T) orientations of the magnetic field with respect to the radiation beam. A 6 MV Varian 2100C Linac provided the radiation component for the measurements. The DUO detector has 505 sensitive volumes (each volume measuring 800 × 40 × 100 µm The penumbral widths measured by the DUO detector demonstrated good agreement with film and the M512 to within an average of 0.5 mm (within uncertainty: ±1 mm). The static inline magnetic field had minimal effect on the profiles in solid water. As expected, the lower density of solid lung meant that this material was more susceptible to demonstrating magnetic field effects in the dose deposited. The greatest penumbral narrowing due to the inline field (0.7 mm) occurred in lung. Central axis dose increase was greatest in lung (maximum: 9%). The transverse field widened penumbra, most notably in the solid lung phantom, by a maximum of 2.3 mm. The largest asymmetry due to the transverse field (4.6%) was also in solid lung. When the air gap above the DUO was filled with bolus, the dose maximum measured by the DUO was within 1.4% of film. The DUO detector has been shown to be successful in accurately describing the dose changes for small field sizes to within a 200-µm resolution in an environment resembling that of an MRI-linac. The DUO measurements were in agreement with both film and the M512 measurements, and therefore the DUO was found to be an appropriate alternative to the M512, with improvement in terms of its higher spatial resolution. MARDOS provided a suitable environment for these preliminary tests before progressing to the MRI-linac.
Publisher: Elsevier BV
Date: 11-12-2004
Publisher: Elsevier BV
Date: 12-2016
DOI: 10.1016/J.EJMP.2016.11.005
Abstract: We present here the latest results from tests performed at the ESRF ID17 and ID21 beamlines for the characterization of novel beam monitors for Microbeam Radiation Therapy (MRT), which is currently being implemented at ID17. MRT aims at treating solid tumors by exploiting an array of evenly spaced microbeams, having an energy spectrum distributed between 27 and 600keV and peaking at 100keV. Given the high instantaneous dose delivered (up to 20kGy/s), the position and the intensity of the microbeams has to be precisely and instantly monitored. For this purpose, we developed dedicated silicon microstrip beam monitors. We have successfully characterized them, both with a microbeam array at ID17, and a submicron scanning beam at ID21. We present here the latest results obtained in recent tests along with an outlook on future developments.
Publisher: Wiley
Date: 30-08-2020
DOI: 10.1118/1.4892384
Abstract: Silicon diode arrays are commonly implemented in radiation therapy quality assurance applications as they have a number of advantages including: real time operation (compared to the film) and high spatial resolution, large dynamic range and small size (compared to ionizing chambers). Most diode arrays have detector pitch that is too coarse for routine use in small field applications. The goal of this work is to characterize the two-dimensional monolithic silicon diode array named "MagicPlate-512" (MP512) designed for QA in stereotactic body radiation therapy (SBRT) and stereotactic radio surgery (SRS). MP512 is a silicon monolithic detector manufactured on ap-type substrate. An array contains of 512 pixels with size 0.5×0.5 mm2 and pitch 2 mm with an overall dimension of 52×52 mm2. The MP512 monolithic detector is wire bonded on a printed circuit board 0.5 mm thick and covered by a thin layer of raisin to preserve the silicon detector from moisture and chemical contamination and to protect the bonding wires. Characterization of the silicon monolithic diode array response was performed, and included pixels response uniformity, dose linearity, percent depth dose, output factor, and beam profiling for beam sizes relevant to SBRT and SRS and depth dose response in comparison with ionization chamber. MP512 shows a good dose linearity (R2=0.998) and repeatability within 0.2%. The measured depth dose response for field size of 10×10 cm2 agreed to within 1.3%, when compared to a CC13 ionization chamber for depths in PMMA up to 30 cm. The output factor of a 6 MV Varian 2100EX medical linac beam measured by MP512 at the isocenter agrees to within 2% when compared to PTW diamond, Scanditronix point EDD-2 diode and MOSkin detectors for field sizes down to 1×1 cm2. An over response of 4% was observed for square beam size smaller than 1 cm when compared to EBT3 films, while the beam profiles (FWHM) of MP512 match to within 2% the data measured by radiochromic film. The response of the 2D detector array, MP512, has been evaluated. The properties of the array demonstrated suitability for use as in phantom dosimeter for QA in SRS and SBRT. Although MP512 matches film measurements down to 1×1 cm2 well, it showed a discrepancy of 4% in the determination of output factors of beams smaller than 0.5×0.5 cm2 due to the field perturbation generated by the large amount of silicon surrounding the central diode. MP512 is highly capable of measuring beam size (FWHM) and has a discrepancy of less than 1.3% when compared to EBT3 film. A reduction in the detector pitch to less than 2 mm would improve the penumbra reconstruction accuracy at the cost readout electronics complexity.
Publisher: IEEE
Date: 11-2016
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 07-07-2022
DOI: 10.36227/TECHRXIV.19555042
Abstract: Hydrogenated amorphous silicon is a well known detector material for its radiation resistance. This study concern 10 µm thickness, p-i-n and charge selective contacts planar diode detectors which were irradiated with neutrons at two fluence values: 1016 neq/cm2 and 5 x 1016 neq/cm2. In order to evaluate their radiation resistance, detector leakage current and response to X-ray photons have been measured. The effect of annealing for performance recovery at 100°C for 12 and 24 hours has also been studied. The results for the 1016 neq/cm2 irradiation show a factor 2 increase in leakage current that is completely recovered after annealing for p-i-n devices while charge selective contacts devices show an overall decrease of the leakage current at the end of the annealing process compared to the measurement before the irradiation. X-ray dosimetric sensitivity degrades, for this fluence, at the end of irradiation but partially recovers for charge selective contacts devices and increases for p-i-n devices at the end of the annealing process. Concerning the 5 x 1016 neq/cm2 irradiation test (for p-i-n structures only), due to the activation that occurred during the irradiation phase, the results were taken after 146 days of storage at around 0° C, during this period, a self-annealing effect may have occurred. Therefore the results after annealing show a small but noticeable degradation in leakage current and x-ray sensitivity, after irradiation and storage.
Publisher: Elsevier BV
Date: 2020
Publisher: Wiley
Date: 17-06-2013
DOI: 10.1118/1.4808360
Abstract: High dose rate (HDR) brachytherapy is a form of radiation therapy for treating prostate cancer whereby a high activity radiation source is moved between predefined positions inside applicators inserted within the treatment volume. Accurate positioning of the source is essential in delivering the desired dose to the target area while avoiding radiation injury to the surrounding tissue. In this paper, HDR BrachyView, a novel inbody dosimetric imaging system for real time monitoring and verification of the radioactive seed position in HDR prostate brachytherapy treatment is introduced. The current prototype consists of a 15 × 60 mm(2) silicon pixel detector with a multipinhole tungsten collimator placed 6.5 mm above the detector. Seven identical pinholes allow full imaging coverage of the entire treatment volume. The combined pinhole and pixel sensor arrangement is geometrically designed to be able to resolve the three-dimensional location of the source. The probe may be rotated to keep the whole prostate within the transverse plane. The purpose of this paper is to demonstrate the efficacy of the design through computer simulation, and to estimate the accuracy in resolving the source position (in detector plane and in 3D space) as part of the feasibility study for the BrachyView project. Monte Carlo simulations were performed using the GEANT4 radiation transport model, with a (192)Ir source placed in different locations within a prostate phantom. A geometrically accurate model of the detector and collimator were constructed. Simulations were conducted with a single pinhole to evaluate the pinhole design and the signal to background ratio obtained. Second, a pair of adjacent pinholes were simulated to evaluate the error in calculated source location. Simulation results show that accurate determination of the true source position is easily obtainable within the typical one second source dwell time. The maximum error in the estimated projection position was found to be 0.95 mm in the imaging (detector) plane, resulting in a maximum source positioning estimation error of 1.48 mm. HDR BrachyView is a feasible design for real-time source tracking in HDR prostate brachytherapy. It is capable of resolving the source position within a subsecond dwell time. In combination with anatomical information obtained from transrectal ultrasound imaging, HDR BrachyView adds a significant quality assurance capability to HDR brachytherapy treatment systems.
Publisher: Elsevier BV
Date: 12-2014
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 03-2022
Publisher: Springer Science and Business Media LLC
Date: 04-11-2016
DOI: 10.1007/S13246-016-0495-1
Abstract: Tracking the position of a moving radiation detector in time and space during data acquisition can replicate 4D image-guided radiotherapy (4DIGRT). Magnetic resonance imaging (MRI)-linacs need MRI-visible detectors to achieve this, however, imaging solid phantoms is an issue. Hence, gel-water, a material that provides signal for MRI-visibility, and which will in future work, replace solid water for an MRI-linac 4DIGRT quality assurance tool, is discussed. MR and CT images of gel-water were acquired for visualisation and electron density verification. Characterisation of gel-water at 0 T was compared to Gammex-RMI solid water, using MagicPlate-512 (M512) and RMI Attix chamber this included percentage depth dose, tissue-phantom ratio (TPR
Publisher: IOP Publishing
Date: 10-2020
DOI: 10.1088/1742-6596/1662/1/012024
Abstract: The goal of this work was to assess small-field output factors (OPF) on a newly commissioned linear accelerator (linac) using a ‘correction-less’ 2D monolithic array of diodes, the Duo, which has a spatial resolution of 0.2 mm. The results would validate a set of OPF extracted from the golden beam data (GBD) used to represent the dosimetric characteristics of that linac, an Elekta Versa HD (Elekta, Crawley), fit with an Agility multileaf collimator (MLC). The Duo acquired relative OPF in real time for square fields of nominal side 1, 2, 3 and 4 cm, for 6 MV with flattening filter (WFF) and 6 MV flattening filter free (FFF) photon energies. Results revealed at most a 1.0% difference in OPF when compared to baseline, and bolstered confidence in the acceptance and commissioning of the linac using local GBD as a baseline match.
Publisher: Wiley
Date: 02-10-2013
DOI: 10.1118/1.4822736
Abstract: High dose rate (HDR) brachytherapy is a radiation treatment technique capable of delivering large dose rates to the tumor. Radiation is delivered using remote afterloaders to drive highly active sources (commonly (192)Ir with an air KERMA strength range between 20,000 and 40,000 U, where 1 U = 1 μGy m(2)/h in air) through applicators directly into the patient's prescribed region of treatment. Due to the obvious ramifications of incorrect treatment while using such an active source, it is essential that there are methods for quality assurance (QA) that can directly and accurately verify the treatment plan and the functionality of the remote afterloader. This paper describes the feasibility study of a QA system for HDR brachytherapy using a phantom based two-dimensional 11 × 11 epitaxial diode array, named "magic phantom." The HDR brachytherapy treatment plan is translated to the phantom with two rows of 10 (20 in total) HDR source flexible catheters, arranged above and below the diode array "magic plate" (MP). Four-dimensional source tracking in each catheter is based upon a developed fast iterative algorithm, utilizing the response of the diodes in close proximity to the (192)Ir source, s led at 100 ms intervals by a fast data acquisition (DAQ) system. Using a (192)Ir source in a solid water phantom, the angular response of the developed epitaxial diodes utilized in the MP and also the variation of the MP response as a function of the source-to-detector distance (SDD) were investigated. These response data are then used by an iterative algorithm for source dwelling position determination. A measurement of the average transit speed between dwell positions was performed using the diodes and a fast DAQ. The angular response of the epitaxial diode showed a variation of 15% within 360°, with two flat regions above and below the detector face with less than 5% variation. For SDD distances of between 5 and 30 mm the relative response of the epitaxial diodes used in the MP is in good agreement (within 8%) with radial dose function measurements found within the TG-43 protocol, with SDD of up to 70 mm showing a 40% over response. A method for four-dimensional localization of the HDR source was developed, allowing the source dwell position to be derived within 0.50 mm of the expected position. An estimation of the average transit speed for varying step sizes was determined and was found to increase from (12.8 ± 0.3) up to (38.6 ± 0.4) cm/s for a step size of 2.5 and 50 mm, respectively. Our characterization of the designed QA "magic phantom" with MP in realistic HDR photon fields demonstrates the promising performance for real-time source position tracking in four dimensions and measurements of transit times. Further development of this system will allow a full suite for QA in HDR brachytherapy and analysis, and for future in vivo tracking.
Publisher: IOP Publishing
Date: 10-2020
DOI: 10.1088/1742-6596/1662/1/012031
Abstract: Diffusing alpha-emitters radiation therapy (DaRT) is a revolutionary brachytherapy technique used to treat solid tumours. Implant seeds are coated with 224 Ra which, along its shortlived daughter atoms, emits alpha particles of high linear energy transfer (LET) and of high relative biological efficiency (RBE), creating a tumour-killing dose distribution a few mm wide. Those alpha particles are of energy between 5.67 and 8.78 MeV. DaRT is under investigation in clinical trials, but there currently is no obvious solution for dosimetry aimed at quality assurance of treatment. This study introduces alpha-RAD, a dosimeter based on a metal-oxide-semiconductor (MOS) sensor technology. Alpha-RAD was characterized with 241 Am, which emits alpha particles of energy 5.49 MeV. The results showed that alpha-RAD had good linearity with dose, with the signal increasing linearly in the range from 0 to 6.84 Gy. Also, an external bias in the range between 15 and 60 V, applied on the gate of alpha-RAD during irradiation, would optimize sensitivity to alpha particles of energies typical of DaRT. Alpha-RAD, owing to its compactness, can fit into a brachytherapy needle, to be placed next to 224 Ra seed implants in the tumour, for real-time in vivo dosimetry.
Publisher: Wiley
Date: 05-06-2018
DOI: 10.1002/ACM2.12364
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 04-2022
Publisher: IEEE
Date: 10-2012
Publisher: IEEE
Date: 2005
Publisher: Elsevier BV
Date: 2018
DOI: 10.1016/J.EJMP.2017.12.010
Abstract: Flattening filter free (FFF) beams are increasingly being considered for stereotactic radiotherapy (SRT). For the first time, the performance of a monolithic silicon array detector under 6 and 10 MV FFF beams was evaluated. The dosimeter, named "Octa" and designed by the Centre for Medical Radiation Physics (CMRP), was tested also under flattened beams for comparison. Output factors (OFs), percentage depth-dose (PDD), dose profiles (DPs) and dose per pulse (DPP) dependence were investigated. Results were benchmarked against commercially available detectors for small field dosimetry. The dosimeter was shown to be a 'correction-free' silicon array detector for OFs and PDD measurements for all the beam qualities investigated. Measured OFs were accurate within 3% and PDD values within 2% compared against the benchmarks. Cross-plane, in-plane and diagonal DPs were measured simultaneously with high spatial resolution (0.3 mm) and real time read-out. A DPP dependence (24% at 0.021 mGy ulse relative to 0.278 mGy ulse) was found and could be easily corrected for in the case of machine specific quality assurance applications. Results were consistent with those for monolithic silicon array detectors designed by the CMRP and previously characterized under flattened beams only, supporting the robustness of this technology for relative dosimetry for a wide range of beam qualities and dose per pulses. In contrast to its predecessors, the design of the Octa offers an exhaustive high-resolution 2D dose map characterization, making it a unique real-time radiation detector for small field dosimetry for field sizes up to 3 cm side.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2014
Publisher: IEEE
Date: 09-2009
Publisher: Wiley
Date: 18-07-2017
DOI: 10.1002/ACM2.12120
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2009
Publisher: Wiley
Date: 06-2018
DOI: 10.1002/ACM2.12360
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2008
Publisher: IOP Publishing
Date: 2019
Publisher: IOP Publishing
Date: 25-04-2018
Publisher: IOP Publishing
Date: 03-05-2016
Publisher: Wiley
Date: 10-07-2017
DOI: 10.1002/MP.12377
Abstract: This study aims to investigate the 2D monolithic silicon diode array size of 52 × 52 mm The MP512 was placed at the center of a cylindrical phantom, irradiated using 6 MV and 10 MV photons and incrementing the incidence of the beam angle in 15° steps from 0° to 180°, and then in 1° steps between 85° and 95°. The MP512 response was characterized for square field sizes varying between 1 × 1 cm The intrinsic angular dependence of the MP512 shows maximum relative deviation from the response normalized to 0° of 18.5 ± 0.5% and 15.5 ± 0.5% for 6 MV and 10 MV, respectively, demonstrating that the angular response is sensitive to the energy. In contrast, the variation of angular response is less affected by field size. Comparison of cross-plane profiles measured by the corrected MP512 and EBT3 shows an agreement within ±2% for all field sizes when the beams irradiated the array at 0°, 45°, 135°, and 180° angles of incidence from the normal to the detector plane. At 90° incidence, corresponding to a depth dose measurement, up to a 6% discrepancy was observed for a 1 × 1 cm An angular correction factor can be adopted for small field sizes. Measurements discrepancies could be encountered when irradiating with very small fields parallel to the detector plane. Using this approach, the MP512 is shown to be a suitable detector for 2D dose mapping of small field size photon beams.
Publisher: Wiley
Date: 13-03-2014
DOI: 10.1118/1.4867858
Abstract: Microbeam Radiation Therapy (MRT), an alternative preclinical treatment strategy using spatially modulated synchrotron radiation on a micrometer scale, has the great potential to cure malignant tumors (e.g., brain tumors) while having low side effects on normal tissue. Dose measurement and calculation in MRT is challenging because of the spatial accuracy required and the arising high dose differences. Dose calculation with Monte Carlo simulations is time consuming and their accuracy is still a matter of debate. In particular, the influence of photon polarization has been discussed in the literature. Moreover, it is controversial whether a complete knowledge of phase space trajectories, i.e., the simulation of the machine from the wiggler to the collimator, is necessary in order to accurately calculate the dose. With Monte Carlo simulations in the Geant4 toolkit, the authors investigate the influence of polarization on the dose distribution and the therapeutically important peak to valley dose ratios (PVDRs). Furthermore, the authors analyze in detail phase space information provided by Martínez‐Rovira et al. [“Development and commissioning of a Monte Carlo photon model for the forthcoming clinical trials in microbeam radiation therapy,” Med. Phys. 39(1), – (2012)] and examine its influence on peak and valley doses. A simple source model is developed using parallel beams and its applicability is shown in a semiadjoint Monte Carlo simulation. Results are compared to measurements and previously published data. Polarization has a significant influence on the scattered dose outside the microbeam field. In the radiation field, however, dose and PVDRs deduced from calculations without polarization and with polarization differ by less than 3%. The authors show that the key consequences from the phase space information for dose calculations are inhomogeneous primary photon flux, partial absorption due to inclined beam incidence outside the field center, increased beam width and center to center distance due to the beam propagation from the collimator to the phantom surface and imperfect absorption in the absorber material of the Multislit Collimator. These corrections have an effect of approximately 10% on the valley dose and suffice to describe doses in MRT within the measurement uncertainties of currently available dosimetry techniques. The source for the first clinical pet trials in MRT is characterized with respect to its phase space and the photon polarization. The results suggest the use of a presented simplified phase space model in dose calculations and hence pave the way for alternative and fast dose calculation algorithms. They also show that the polarization is of minor importance for the clinical important peak and valley doses inside the microbeam field.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2201
Publisher: AIP Publishing
Date: 12-2018
DOI: 10.1063/1.5052059
Abstract: A common approach for spectrum determination of polyenergetic proton bunches from laser-ion acceleration experiments is based on the time-of-flight (TOF) method. However, spectra obtained using this method are typically given in relative units or are estimated based on some prior assumptions on the energy distribution of the accelerated ions. In this work, we present a new approach using the TOF method that allows for an absolute energy spectrum reconstruction from a current signal acquired with a sub-nanosecond fast and 10 µm thin silicon detector. The reconstruction is based on solving a linear least-squares problem, taking into account the response function of the detection system. The general principle of signal generation and spectrum reconstruction by setting up an appropriate system response matrix is presented. Proof-of-principle experiments at a 12 MV Tandem accelerator using different nanosecond-short (quasi-)monoenergetic and polyenergetic proton bunches at energies up to 20 MeV were successfully performed. Within the experimental uncertainties of 2.4% and 12.1% for energy and particle number, respectively, reconstructed energy distributions were found in excellent agreement with the spectra calculated using Monte Carlo simulations and measured by a magnetic spectrometer. This TOF method can hence be used for absolute online spectrometry of laser-accelerated particle bunches.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 09-2018
Publisher: MDPI AG
Date: 06-01-2022
DOI: 10.3390/APP12020537
Abstract: A large area pixelated silicon array detector named “MP987” has been developed for in vivo dosimetry. The detector was developed to overcome the non-water equivalent response of EPID (Electronic Portal Imaging Device) dosimetry systems, due to the shortfalls of the extensive corrections required. The detector, readout system and software have all been custom designed to be operated independently from the linac with the array secured directly above the EPID, to be used in combination with the 6 MV imaging system. Dosimetry characterisation measurements of percentage depth dose (PDD), dose rate dependence, radiation damage, output factors (OF), profile measurements, linearity and uniformity were performed. Additionally, the first pre-clinical tests with this novel detector of a transit dosimetry characterization and a collapsed IMRT (intensity-modulated radiation therapy) study are presented. Both PDD and OF measurements had a percentage difference of less than 2.5% to the reference detector. A maximum change in sensitivity of 4.3 ± 0.3% was observed after 30 kGy of gamma accumulated dose. Transit dosimetry measurements through a homogeneous Solid Water phantom had a measured dose within error of the TPS calculations, for field sizes between 3 × 3 cm2 and 10 × 10 cm2. A four-fraction collapsed IMRT plan on a lung phantom had absolute dose pass fractions between the MP987 and TPS (treatment planning system) from 94.2% to 97.4%, with a 5%/5 mm criteria. The ability to accurately measure dose at a transit level, without the need for correction factors derived from extensive commissioning data collection procedures, makes the MP987 a viable alternative to the EPID for in vivo dosimetry. This MP987 is this first of its kind to be successfully developed specifically for a dual detector application.
Publisher: Elsevier BV
Date: 10-2019
DOI: 10.1016/J.EJMP.2019.09.237
Abstract: BrachyView is a novel in-body imaging system developed with the objective to provide real-time intraoperative dosimetry for low dose rate (LDR) prostate brachytherapy treatments. The BrachyView coordinates combined with conventional transrectal ultrasound (TRUS) imaging, provides the possibility to localise the effective position of the implanted seeds inside the prostate volume, providing a unique tool for intra-operative verification of the quality of the implantation. This research presents the first complete LDR brachytherapy plan reconstructed by the BrachyView system and is used to evaluate the effectiveness of an imaging algorithm with baseline subtraction. A plan featuring 98 I-125 brachytherapy seeds, with an average activity of 0.248 mCi, were implanted into a prostate gel phantom under TRUS guidance. Images of implanted seeds were obtained by the BrachyView after the implantation of seeds. The baseline subtraction algorithm is applied as a pixel-to-pixel counts subtraction and is applied to every second projection obtained after the implantation of each needle. Seed positions and effectiveness of the baseline reconstruction in the identification of seeds were verified by a high-resolution post-implant CT scan. A complete brachytherapy plan has been reconstructed with a 100% detection rate. This is possible due to the effectiveness of the baseline subtraction, with its application an overall increase of 11.3% in position accuracy and 8.2% increase in detection rate was noted. It has been demonstrated that the BrachyView system shows the potential to be a solution to providing clinics with the means for intraoperative dosimetry for LDR prostate brachytherapy treatments.
Publisher: IOP Publishing
Date: 10-2020
DOI: 10.1088/1742-6596/1662/1/012021
Abstract: The reference adult male and female voxel phantoms described in the International Commission on Radiological Protection (ICRP) publication 110 have been successfully implemented in a Geant4 application named ICRP110Phantoms . The application allows users to simulate either the whole or a partial phantom, including as little as a single cross-sectional slice. The Geant4 application allows users to estimate the absorbed dose in in idual voxels and in entire organs. As ex le of application, the ICRP110Phantoms was used to estimate the dose deposited by a mono-energetic 125 MeV proton pencil beam, incident on the left breast and passing through the lungs and heart, modelled in partial chest phantoms of both male and female ICRP110 phantoms. The ICRP110Phantoms will be released in Geant4 as an Advanced Ex le to allow its use in the wider scientific community. This Geant4 Advanced Ex le application can be utilised for dosimetric studies in radiotherapy, nuclear medicine and radiation protection.
Publisher: Elsevier BV
Date: 12-2010
Publisher: Wiley
Date: 22-11-2019
DOI: 10.1002/ACM2.12496
Publisher: Elsevier BV
Date: 12-2014
Publisher: American Chemical Society (ACS)
Date: 22-11-2021
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2012
Publisher: Wiley
Date: 18-04-2012
DOI: 10.1118/1.3700234
Abstract: Intensity modulated radiation therapy (IMRT) utilizes the technology of multileaf collimators to deliver highly modulated and complex radiation treatment. Dosimetric verification of the IMRT treatment requires the verification of the delivered dose distribution. Two dimensional ion chamber or diode arrays are gaining popularity as a dosimeter of choice due to their real time feedback compared to film dosimetry. This paper describes the characterization of a novel 2D diode array, which has been named the "magic plate" (MP). It was designed to function as a 2D transmission detector as well as a planar detector for dose distribution measurements in a solid water phantom for the dosimetric verification of IMRT treatment delivery. The prototype MP is an 11 × 11 detector array based on thin (50 μm) epitaxial diode technology mounted on a 0.6 mm thick Kapton substrate using a proprietary "drop-in" technology developed by the Centre for Medical Radiation Physics, University of Wollongong. A full characterization of the detector was performed, including radiation damage study, dose per pulse effect, percent depth dose comparison with CC13 ion chamber and build up characteristics with a parallel plane ion chamber measurements, dose linearity, energy response and angular response. Postirradiated magic plate diodes showed a reproducibility of 2.1%. The MP dose per pulse response decreased at higher dose rates while at lower dose rates the MP appears to be dose rate independent. The depth dose measurement of the MP agrees with ion chamber depth dose measurements to within 0.7% while dose linearity was excellent. MP showed angular response dependency due to the anisotropy of the silicon diode with the maximum variation in angular response of 10.8% at gantry angle 180°. Angular dependence was within 3.5% for the gantry angles ± 75°. The field size dependence of the MP at isocenter agrees with ion chamber measurement to within 1.1%. In the beam perturbation study, the surface dose increased by 12.1% for a 30 × 30 cm(2) field size at the source to detector distance (SDD) of 80 cm whilst the transmission for the MP was 99%. The radiation response of the magic plate was successfully characterized. The array of epitaxial silicon based detectors with "drop-in" packaging showed properties suitable to be used as a simplified multipurpose and nonperturbing 2D radiation detector for radiation therapy dosimetric verification.
Publisher: Wiley
Date: 27-05-2021
Abstract: A new printable organic semiconducting material combination as a tissue equivalent photodetector for indirect X‐ray detection is demonstrated in this work. The device exhibits a higher optical‐to‐electrical conversion efficiency than any other reported printable organic systems for X‐ray photodetection while also operating efficiently with zero applied bias. Complete X‐ray detectors fabricated by coupling the photodiode with a plastic scintillator are among the first flexible and fully tissue equivalent X‐ray detectors capable of operating without external bias. The response to X‐rays is energy independent between 50 keV and 1.2 MeV, with a detection sensitivity equivalent to inorganic direct X‐ray detectors and one of the fastest temporal responses ever reported for organic X‐ray detectors. The materials can be printed into arrays with a pixel pitch of 120 μm, providing 2D spatial detection. The devices are found to be highly stable with respect to time, mechanical flexing, and large (5 kGy) radiation doses. The new materials and fully tissue equivalent X‐ray detectors reported here provide stable, printable, flexible, and tissue equivalent detectors with a high radiolucency that are ideally suited for wearable applications, where simultaneous monitoring and high transmission of the X‐ray absorbed dose into the human body is required.
Publisher: IOP Publishing
Date: 10-2020
DOI: 10.1088/1742-6596/1662/1/012008
Abstract: Multiple vendors are now offering real-time MRI-guided radiotherapy systems. Quality assurance of the imaging and radiation isocentre alignment is an essential component of the QA programme for any linear accelerator used for delivering image-guided radiotherapy. In this work, the authors describe the design and feasibility testing of a device that combines a high resolution monolithic silicon strip detector with an MRI visible phantom for characterisation of optical, MR imaging and radiation isocentre for inline MR-guided radiotherapy systems.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2015
Publisher: Wiley
Date: 19-04-2022
DOI: 10.1002/MP.15658
Abstract: The purpose of this study was to examine the effect of departmental planning techniques on appropriate in‐vivo source tracking error thresholds for high dose rate (HDR) prostate brachytherapy (BT) treatments, and to determine if a single in‐vivo source tracking error threshold would be appropriate for the same patient anatomy. The prostate, rectum, and urethra were contoured on a single patient transrectal ultrasound (TRUS) dataset. Anonymized DICOM files were disseminated to 16 departments who created an HDR prostate BT treatment plan on the dataset with a prescription dose of 15 Gy in a single fraction. Departments were asked to follow their own local treatment planning guidelines. Source positioning errors were then simulated in the 16 treatment plans and the effect on dose–volume histogram (DVH) indices calculated. Change in DVH indices were used to determine appropriate in‐vivo source tracking error thresholds. Plans were considered to require intervention if the following DVH conditions occurred: prostate V100% 90%, urethra D0.1cc 118%, and rectumtt D max 80%. There was wide variation in appropriate in‐vivo source tracking error thresholds among the 16 participating departments, ranging from 1 to 6 mm. Appropriate in‐vivo source tracking error thresholds were also found to depend on the direction of the source positioning error and the endpoint. A robustness parameter was derived, and found to correlate with the sensitivity of plans to source positioning errors. A single HDR prostate BT in‐vivo source tracking error threshold cannot be applied across multiple departments, even for the same patient anatomy. The burden on in‐vivo source tracking devices may be eased through improving HDR prostate BT plan robustness during the plan optimisation phase.
Publisher: IOP Publishing
Date: 10-2020
DOI: 10.1088/1742-6596/1662/1/012007
Abstract: In the present work, we reported on the use of a new 2D array of diodes, the Duo, for dosimetry of small beams produced with a CyberKnife system, and shaped with a novel multi-leaf collimator, the InCise 2.
Publisher: Elsevier BV
Date: 03-2007
Publisher: IOP Publishing
Date: 03-04-2020
Publisher: Wiley
Date: 14-10-2019
DOI: 10.1002/ACM2.12744
Publisher: Wiley
Date: 11-04-2020
DOI: 10.1002/ACM2.12864
Publisher: Wiley
Date: 12-01-2015
DOI: 10.1118/1.4905233
Abstract: High dose rate (HDR) brachytherapy is a treatment method that is used increasingly worldwide. The development of a sound quality assurance program for the verification of treatment deliveries can be challenging due to the high source activity utilized and the need for precise measurements of dwell positions and times. This paper describes the application of a novel phantom, based on a 2D 11 × 11 diode array detection system, named “magic phantom” (MPh), to accurately measure plan dwell positions and times, compare them directly to the treatment plan, determine errors in treatment delivery, and calculate absorbed dose. The magic phantom system was CT scanned and a 20 catheter plan was generated to simulate a nonspecific treatment scenario. This plan was delivered to the MPh and, using a custom developed software suite, the dwell positions and times were measured and compared to the plan. The original plan was also modified, with changes not disclosed to the primary authors, and measured again using the device and software to determine the modifications. A new metric, the “position–time gamma index,” was developed to quantify the quality of a treatment delivery when compared to the treatment plan. The MPh was evaluated to determine the minimum measurable dwell time and step size. The incorporation of the TG-43U1 formalism directly into the software allows for dose calculations to be made based on the measured plan. The estimated dose distributions calculated by the software were compared to the treatment plan and to calibrated EBT3 film, using the 2D gamma analysis method. For the original plan, the magic phantom system was capable of measuring all dwell points and dwell times and the majority were found to be within 0.93 mm and 0.25 s, respectively, from the plan. By measuring the altered plan and comparing it to the unmodified treatment plan, the use of the position–time gamma index showed that all modifications made could be readily detected. The MPh was able to measure dwell times down to 0.067 ± 0.001 s and planned dwell positions separated by 1 mm. The dose calculation carried out by the MPh software was found to be in agreement with values calculated by the treatment planning system within 0.75%. Using the 2D gamma index, the dose map of the MPh plane and measured EBT3 were found to have a pass rate of over 95% when compared to the original plan. The application of this magic phantom quality assurance system to HDR brachytherapy has demonstrated promising ability to perform the verification of treatment plans, based upon the measured dwell positions and times. The introduction of the quantitative position–time gamma index allows for direct comparison of measured parameters against the plan and could be used prior to patient treatment to ensure accurate delivery.
Publisher: IEEE
Date: 2005
Publisher: IOP Publishing
Date: 2017
Publisher: Elsevier BV
Date: 05-2008
Publisher: Elsevier BV
Date: 02-2017
DOI: 10.1016/J.EJMP.2017.01.012
Abstract: BrachyView is a novel in-body imaging system which aims to provide LDR brachytherapy seeds position reconstruction within the prostate in real-time. The first prototype is presented in this study: the probe consists of a gamma camera featuring three single cone pinhole collimators embedded in a tungsten tube, above three, high resolution pixelated detectors (Timepix). The prostate was imaged with a TRUS system using a sagittal crystal with a 2.5mm slice thickness. Eleven needles containing a total of thirty 0.508U The reconstructed seed positions determined by the BrachyView probe showed a maximum discrepancy of 1.78mm, with 75% of the seeds reconstructed within 1mm of their nominal location. An accurate co-registration between the BrachyView and TRUS coordinate system was established. The BrachyView system has shown its ability to reconstruct all implanted LDR seeds within a tissue equivalent prostate gel phantom, providing both anatomical and seed position information in a single interface.
Publisher: IOP Publishing
Date: 2017
Publisher: Elsevier BV
Date: 05-2010
Publisher: IEEE
Date: 10-2013
Publisher: Oxford University Press (OUP)
Date: 21-01-2019
DOI: 10.1093/RPD/NCY234
Abstract: An experimental and simulation-based study was performed on a 12C ion minibeam radiation therapy (MBRT) field produced with a clinical broad beam and a brass multi-slit collimator (MSC). Silicon-on-insulator (SOI) microdosimeters developed at the Centre for Medical Radiation Physics (CMRP) with micron sized sensitive volumes were used to measure the microdosimetric spectra at varying positions throughout the MBRT field and the corresponding dose-mean lineal energies and RBE for 10% cell survival (RBE10) were calculated using the modified Microdosimetric Kinetic Model (MKM). An increase in the average RBE10 of ∼30% and 10% was observed in the plateau region compared to broad beam for experimental and simulation values, respectively. The experimental collimator misalignment was determined to be 0.7° by comparison between measured and simulated microdosimetric spectra at varying collimator angles. The simulated dose-mean lineal energies in the valley region between minibeams were found to be higher on average than in the minibeams due to higher LET particles being produced in these regions from the MSC. This work presents the first experimental microdosimetry measurements and characterisation of the local biological effectiveness in a MBRT field.
Publisher: International Union of Crystallography (IUCr)
Date: 08-07-2021
DOI: 10.1107/S1600577521006044
Abstract: Spatially fractionated ultra-high-dose-rate beams used during microbeam radiation therapy (MRT) have been shown to increase the differential response between normal and tumour tissue. Quality assurance of MRT requires a dosimeter that possesses tissue equivalence, high radiation tolerance and spatial resolution. This is currently an unsolved challenge. This work explored the use of a 500 nm thick organic semiconductor for MRT dosimetry on the Imaging and Medical Beamline at the Australian Synchrotron. Three beam filters were used to irradiate the device with peak energies of 48, 76 and 88 keV with respective dose rates of 3668, 500 and 209 Gy s −1 . The response of the device stabilized to 30% efficiency after an irradiation dose of 30 kGy, with a 0.5% variation at doses of 35 kGy and higher. The calibration factor after pre-irradiation was determined to be 1.02 ± 0.005 µGy per count across all three X-ray energy spectra, demonstrating the unique advantage of using tissue-equivalent materials for dosimetry. The percentage depth dose curve was within ±5% of the PTW microDiamond detector. The broad beam was fractionated into 50 microbeams (50 µm FHWM and 400 µm centre-to-centre distance). For each beam filter, the FWHMs of all 50 microbeams were measured to be 51 ± 1.4, 53 ± 1.4 and 69 ± 1.9 µm, for the highest to lowest dose rate, respectively. The variation in response suggested the photodetector possessed dose-rate dependence. However, its ability to reconstruct the microbeam profile was affected by the presence of additional dose peaks adjacent to the one generated by the X-ray microbeam. Geant4 simulations proved that the additional peaks were due to optical photons generated in the barrier film coupled to the sensitive volume. The simulations also confirmed that the litude of the additional peak in comparison with the microbeam decreased for spectra with lower peak energies, as observed in the experimental data. The material packaging can be optimized during fabrication by solution processing onto a flexible substrate with a non-fluorescent barrier film. With these improvements, organic photodetectors show promising prospects as a cost-effective high spatial resolution tissue-equivalent flexible dosimeter for synchrotron radiation fields.
Publisher: Wiley
Date: 06-2013
DOI: 10.1118/1.4815685
Publisher: Elsevier BV
Date: 04-2021
Publisher: Wiley
Date: 13-01-2021
DOI: 10.1002/ACM2.13160
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2014
Publisher: Wiley
Date: 23-06-2021
DOI: 10.1002/MP.14905
Abstract: A 5 and 10 μm thin silicon on insulator (SOI) 3D mushroom microdosimeter was used to characterize both the in‐field and out‐of‐field of a 62 MeV proton beam. The SOI mushroom microdosimeter consisted of an array of cylindrical sensitive volumes (SVs), developed by the Centre for Medical Radiation Physics, University of Wollongong, was irradiated with 62 MeV protons at the CATANA (Centro di AdroTerapia Applicazioni Nucleari Avanzate) facility in Catania, Italy, a facility dedicated to the radiation treatment of ocular melanomas. Dose mean lineal energy, ( ), values were obtained at various depths in PMMA along a pristine and spread out Bragg peak (SOBP). The measured microdosimetric spectra at each position were then used as inputs into the modified Microdosimetric Kinetic Model (MKM) to derive the RBE for absorbed dose in a middle of the SOBP 2Gy (RBE D ). Microdosimetric spectra were obtained with both the 5 and 10 μm 3D SOI microdosimeters, with a focus on the distal part of the BP. The in‐field and out‐of‐field measurement configurations along the Bragg curve were modeled in Geant4 for comparison with experimental results. Lateral out‐of‐field measurements were performed to study secondary particles’ contribution to normal tissue’s dose, up to 12 mm from the edge of the beam field, and quality factor and dose equivalent results were obtained. Comparison between experimental and simulation results showed good agreement between one another for both the pristine and SOBP beams in terms of and RBED. Though a small discrepancy between experiment and simulation was seen at the entrance of the Bragg curve, where experimental results were slightly lower than Geant4. The dose equivalent value measured 12 mm from the edge of the target volume was 1.27 ± 0.15 mSv/Gy with a value of 2.52 ± 0.30, both of which agree within uncertainty with Geant4 simulation. These results demonstrate that SOI microdosimeters are an effective tool to predict RBED in‐field as well as dose equivalent monitoring out‐of‐field to provide insight to probability of second cancer generation.
Publisher: Elsevier BV
Date: 11-2017
Publisher: Elsevier BV
Date: 09-2015
DOI: 10.1016/J.EJMP.2015.04.016
Abstract: Stereotactic Synchrotron Radiotherapy (SSRT) and Microbeam Radiation Therapy (MRT) are both novel approaches to treat brain tumor and potentially other tumors using synchrotron radiation. Although the techniques differ by their principles, SSRT and MRT share certain common aspects with the possibility of combining their advantages in the future. For MRT, the technique uses highly collimated, quasi-parallel arrays of X-ray microbeams between 50 and 600 keV. Important features of highly brilliant Synchrotron sources are a very small beam ergence and an extremely high dose rate. The minimal beam ergence allows the insertion of so called Multi Slit Collimators (MSC) to produce spatially fractionated beams of typically ∼25-75 micron-wide microplanar beams separated by wider (100-400 microns center-to-center(ctc)) spaces with a very sharp penumbra. Peak entrance doses of several hundreds of Gy are extremely well tolerated by normal tissues and at the same time provide a higher therapeutic index for various tumor models in rodents. The hypothesis of a selective radio-vulnerability of the tumor vasculature versus normal blood vessels by MRT was recently more solidified. SSRT (Synchrotron Stereotactic Radiotherapy) is based on a local drug uptake of high-Z elements in tumors followed by stereotactic irradiation with 80 keV photons to enhance the dose deposition only within the tumor. With SSRT already in its clinical trial stage at the ESRF, most medical physics problems are already solved and the implemented solutions are briefly described, while the medical physics aspects in MRT will be discussed in more detail in this paper.
Publisher: IOP Publishing
Date: 2017
Publisher: Elsevier BV
Date: 09-2006
Publisher: Wiley
Date: 03-06-2020
DOI: 10.1002/MP.14229
Abstract: The development of novel detectors for dosimetry in advanced radiotherapy modalities requires materials that have a water equivalent response to ionizing radiation such that characterization of radiation beams can be performed without the need for complex calibration procedures and correction factors. Organic semiconductors are potentially an ideal technology in fabricating devices for dosimetry due to tissue equivalence, mechanical flexibility, and relatively cheap manufacturing cost. The response of a commercial organic photodetector (OPD), coupled to a plastic scintillator, to ionizing radiation from a linear accelerator and orthovoltage x‐ray tube has been characterized to assess its potential as a dosimeter for radiotherapy. The radiation hardness of the OPD has also been investigated to demonstrate its longevity for such applications. Radiation hardness measurements were achieved by observing the response of the OPD to the visible spectrum and 70 keV x rays after pre‐exposure to 40 kGy of ionizing radiation. The response of a preirradiated OPD to 6‐MV photons from a linear accelerator in reference conditions was compared to a nonirradiated OPD with respect to direct and indirect (RP400 plastic scintillator) detection mechanisms. Dose rate dependence of the OPD was measured by varying the surface‐to‐source distance between 90 and 300 cm. Energy dependence was characterized from 29.5 to 129 keV with an x‐ray tube. The percentage depth dose (PDD) curves were measured from 0.5 to 20 cm and compared to an ionization chamber. The OPD sensitivity to visible light showed substantial degradation of the broad 450 to 600 nm peak from the donor after irradiation to 40 kGy. After irradiation, the spectral shape has a dominant absorbance peak at 370 nm, as the acceptor better withstood radiation damage. Its response to x rays stabilized to 30% after 35 kGy, with a 0.5% difference between 770 Gy increments. The OPD exhibited reproducible detection of ionizing radiation when coupled with a scintillator. Indirect detection showed a linear response from 25 to 500 cGy and constant response to dose rates from 0.31 Gy ulse to 3.4 × 10 −4 Gy ulse. However, without the scintillator, response increased by 100% at low dose rates. Energy independence between 100 keV and 1.2 MeV advocates their use as a dosimeter without beam correction factors. A dependence on the scintillator thickness used during a comparison of the PDD to the ionizing chamber was identified. A 1‐mm‐thick scintillator coupled with the OPD demonstrated the best agreement of ± 3%. The response of OPDs to ionizing radiation has been characterized, showing promising use as a dosimeter when coupled with a plastic scintillator. The mechanisms of charge transport and trapping within organic materials varies for visible and ionizing radiation, due to differing properties for direct and indirect detection mechanisms and observing a substantial decrease in sensitivity to the visible spectrum after 40 kGy. This study proved that OPDs produce a stable response to 6‐MV photons, and with a deeper understanding of the charge transport mechanisms due to exposure to ionizing radiation, they are promising candidates as the first flexible, water equivalent, real‐time dosimeter.
Publisher: IOP Publishing
Date: 2017
Publisher: Wiley
Date: 18-07-2020
DOI: 10.1002/ACM2.12967
Publisher: IOP Publishing
Date: 2017
Publisher: Elsevier BV
Date: 08-2018
Publisher: IOP Publishing
Date: 2017
Publisher: IEEE
Date: 10-2011
Publisher: Springer Science and Business Media LLC
Date: 21-02-2019
DOI: 10.1007/S13246-019-00736-7
Abstract: A family of prototype 2D monolithic silicon-diode array detectors (MP512, Duo, Octa) has been proposed by the Centre for Medical Radiation Physics, University of Wollongong (Australia) for relative dosimetry in small megavoltage photon beams. These detectors, which differ in the topology of their 512 sensitive volumes, were originally fabricated on bulk p-type substrates. More recently, they have also been fabricated on epitaxial p-type substrates. In the literature, their performance has been in idually characterized for quality assurance (QA) applications. The present study directly assessed and compared that of a MP512-bulk and that of a MP512-epitaxial in terms of radiation hardness, long-term stability, response linearity with dose, dose per pulse and angular dependence. Their measurements of output factors, off-axis ratios and percentage depth doses in square radiation fields collimated by the jaws and produced by 6 MV and 10 MV flattened photon beams were then benchmarked against those by commercially available detectors. The present investigation was aimed at establishing, from a medical physicist's perspective, how the bulk and epitaxial fabrication technologies would affect the implementation of the MP512s into a QA protocol. Based on results, the MP512-epitaxial would offer superior radiation hardness, long-term stability and achievable uniformity and reproducibility of the response across the 2D active area.
Publisher: Elsevier BV
Date: 11-2022
DOI: 10.1016/J.BRACHY.2022.07.011
Abstract: The purpose of this study was to determine the feasibility of online adaptive transrectal ultrasound (TRUS)-based high-dose-rate prostate brachytherapy (HDRPBT) through retrospective simulation of source positioning and catheter swap errors on patient treatment plans. Source positioning errors (catheter shifts in 1 mm increments in the cranial/caudal, anterior osterior, and medial/lateral directions up to ±6 mm) and catheter swap errors (between the most and least heavily weighted) were introduced retrospectively into DICOM treatment plans of 20 patients that previously received TRUS HDRPBT. Dose volume histogram (DVH) indices were monitored as errors were introduced sequentially into in idual catheters, simulating potential errors throughout treatment. Whenever DVH indices were outside institution thresholds: prostate V100% 118% and rectum Dmax >80%, the plan was adapted using remaining catheters (i.e., simulating previous catheters as previously delivered). The final DVH indices were recorded. Prostate coverage (V100% >95%) could be maintained for source position errors up to 6 mm through online plan adaptation. The source position error at which the urethra D0.1cc and rectum Dmax was able to return to clinically acceptable levels using online adaptation varied between 6 mm to 1 mm, depending on the direction of the source position error and patient anatomy. After introduction of catheter swap errors to patient plans, prostate V100% was recoverable using online adaptation to near original plan characteristics. Urethra D0.1cc and rectum Dmax showed less recoverability. Online adaptive HDRPBT maintains the prostate V100% to clinically acceptable values for majority of directional shifts. However, the current online adaptive method may not correct for source position errors near organs at risk.
Publisher: IOP Publishing
Date: 2017
Publisher: Springer Science and Business Media LLC
Date: 20-03-2014
DOI: 10.1007/S13246-014-0261-1
Abstract: Contemporary radiation therapy (RT) is complicated and requires sophisticated real-time quality assurance (QA). While 3D real-time dosimetry is most preferable in RT, it is currently not fully realised. A small, easy to use and inexpensive point dosimeter with real-time and in vivo capabilities is an option for routine QA. Such a dosimeter is essential for skin, in vivo or interface dosimetry in phantoms for treatment plan verification. The metal-oxide-semiconductor-field-effect-transistor (MOSFET) detector is one of the best choices for these purposes, however, the MOSFETs sensitivity and its signal stability degrade after essential irradiation which limits its lifespan. The accumulation of positive charge on the gate oxide and the creation of interface traps near the silicon-silicon dioxide layer is the primary physical phenomena responsible for this degradation. The aim of this study is to investigate MOSFET dosimeter recovery using two proposed annealing techniques: direct current (DC) and pulsed current (PC), both based on hot charged carrier injection into the gate oxide of the p-MOSFET dosimeter. The investigated MOSFETs were reused multiple times using an irradiation-annealing cycle. The effect of the current-annealing parameters was investigated for the dosimetric characteristics of the recovered MOSFET dosimeters such as linearity, sensitivity and initial threshold voltage. Both annealing techniques demonstrated excellent results in terms of maintaining a stable response, linearity and sensitivity of the MOSFET dosimeter. However, PC annealing is more preferable than DC annealing as it offers better dose response linearity of the reused MOSFET and has a very short annealing time.
Publisher: Wiley
Date: 14-02-2011
DOI: 10.1118/1.3549759
Abstract: Stereotactic radiosurgery/therapy (SRS/SRT) is the use of radiation ablation in place of conventional surgical excision to remove or create fibrous tissue in small target volumes. The target of the SRT/SRS treatment is often located in close proximity to critical organs, hence the requirement of high geometric precision including a tight margin on the planning target volume and a sharp dose fall off. One of the major problems with quality assurance (QA) of SRT/SRS is the availability of suitable detectors with the required spatial resolution. The authors present a novel detector that they refer to as the dose magnifying glass (DMG), which has a high spatial resolution (0.2 mm) and is capable of meeting the stringent requirements of QA and dosimetry in SRS/SRT therapy. The DMG is an array of 128 phosphor implanted n+ strips on a p-type Si wafer. The sensitive area defined by a single n+ strip is 20 x 2000 microm2. The Si wafer is 375 microm thick. It is mounted on a 0.12 mm thick Kapton substrate. The authors studied the dose per pulse (dpp) and angular response of the detector in a custom-made SRS phantom. The DMG was used to determine the centers of rotation and positioning errors for the linear accelerator's gantry, couch, and collimator rotations. They also used the DMG to measure the profiles and the total scatter factor (S(cp)) of the SRS cones. Comparisons were made with the EBT2 film and standard S(cp) values. The DMG was also used for dosimetric verification of a typical SRS treatment with various noncoplanar fields and arc treatments when applied to the phantom. The dose per pulse dependency of the DMG was found to be < 5% for a dpp change of 7.5 times. The angular response of the detector was investigated in the azimuthal and polar directions. The maximum polar angular response was 13.8% at the gantry angle of 320 degrees, which may be partly due to the phantom geometry. The maximum azimuthal angular response was 15.3% at gantry angles of 90 degrees and 270 degrees. The angular response at the gantry angle of 180 degrees was 6.3%. A correction function was derived to correct for the angular dependence of the detector, which takes into account the contribution of the azimuthal and polar angular response at different treatment couch positions. The maximum positioning errors due to collimator, gantry, and couch rotation were 0.2 +/- 0.1, 0.4 +/- 0.1, and 0.4 +/- 0.2 mm, respectively. The SRS cone S(cp) agrees very well with the standard data with an average difference of 1.2 +/- 1.1%. Comparison of the relative intensity profiles of the DMG and EBT2 measurements for a simulated SRS treatment shows a maximum difference of 2.5%. The DMG was investigated for dose per pulse and angular dependency. Its application to SRS/SRT delivery verification was demonstrated. The DMG with its high spatial resolution and real time capability allows measurement of dose profiles for cone applicators down to 5 mm in diameter, both accurately and rapidly as required in typical SRS/SRT deliveries.
Publisher: Wiley
Date: 06-01-2010
DOI: 10.1118/1.3264176
Abstract: Intensity modulated radiation therapy (IMRT) allows the delivery of escalated radiation dose to tumor while sparing adjacent critical organs. In doing so, IMRT plans tend to incorporate steep dose gradients at interfaces between the target and the organs at risk. Current quality assurance (QA) verification tools such as 2D diode arrays, are limited by their spatial resolution and conventional films are nonreal time. In this article, the authors describe a novel silicon strip detector (CMRP DMG) of high spatial resolution (200 microm) suitable for measuring the high dose gradients in an IMRT delivery. A full characterization of the detector was performed, including dose per pulse effect, percent depth dose comparison with Farmer ion chamber measurements, stem effect, dose linearity, uniformity, energy response, angular response, and penumbra measurements. They also present the application of the CMRP DMG in the dosimetric verification of a clinical IMRT plan. The detector response changed by 23% for a 390-fold change in the dose per pulse. A correction function is derived to correct for this effect. The strip detector depth dose curve agrees with the Farmer ion chamber within 0.8%. The stem effect was negligible (0.2%). The dose linearity was excellent for the dose range of 3-300 cGy. A uniformity correction method is described to correct for variations in the in idual detector pixel responses. The detector showed an over-response relative to tissue dose at lower photon energies with the maximum dose response at 75 kVp nominal photon energy. Penumbra studies using a Varian Clinac 21EX at 1.5 and 10.0 cm depths were measured to be 2.77 and 3.94 mm for the secondary collimators, 3.52 and 5.60 mm for the multileaf collimator rounded leaf ends, respectively. Point doses measured with the strip detector were compared to doses measured with EBT film and doses predicted by the Philips Pinnacle treatment planning system. The differences were 1.1% +/- 1.8% and 1.0% +/- 1.6%, respectively. They demonstrated the high temporal resolution capability of the detector readout system, which will allow one to investigate the temporal dose pattern of IMRT and volumetric modulated are therapy (VMAT) deliveries. The CMRP silicon strip detector dose magnifying glass interfaced to a TERA ASIC DAQ system has high spatial and temporal resolution. It is a novel and valuable tool for QA in IMRT dose delivery and for VMAT dose delivery.
Publisher: Springer Science and Business Media LLC
Date: 29-09-2017
DOI: 10.1038/S41598-017-12697-6
Abstract: Synchrotron microbeam radiation therapy is a novel external beam therapy under investigation, that uses highly brilliant synchrotron x-rays in microbeams 50 μ m width, with separation of 400 μ m, as implemented here. Due to the fine spatial fractionation dosimetry of these beams is a challenging and complicated problem. In this proof-of-concept work, we present a fibre optic dosimeter that uses plastic scintillator as the radiation conversion material. We claim an ideal one-dimensional resolution of 50 μ m. Using plastic scintillator and fibre optic makes this dosimeter water-equivalent, a very desirable dosimetric property. The dosimeter was tested at the Australian Synchrotron, on the Imaging and Medical Beam-Line. The in idual microbeams were able to be resolved and the peak-to-valley dose ratio and the full width at half maximum of the microbeams was measured. These results are compared to a semiconductor strip detector of the same spatial resolution. A percent depth dose was measured and compared to data acquired by an ionisation chamber. The results presented demonstrate significant steps towards the development of an optical dosimeter with the potential to be applied in quality assurance of microbeam radiation therapy, which is vital if clinical trials are to be performed on human patients.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 04-2015
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2005
Publisher: Wiley
Date: 06-07-0016
DOI: 10.1002/MP.12736
Abstract: The measurement of depth dose profiles for range and energy verification of heavy ion beams is an important aspect of quality assurance procedures for heavy ion therapy facilities. The steep dose gradients in the Bragg peak region of these profiles require the use of detectors with high spatial resolution. The aim of this work is to characterize a one dimensional monolithic silicon detector array called the "serial Dose Magnifying Glass" (sDMG) as an independent ion beam energy and range verification system used for quality assurance conducted for ion beams used in heavy ion therapy. The sDMG detector consists of two linear arrays of 128 silicon sensitive volumes each with an effective size of 2mm × 50μm × 100μm fabricated on a p-type substrate at a pitch of 200 μm along a single axis of detection. The detector was characterized for beam energy and range verification by measuring the response of the detector when irradiated with a 290 MeV/u The relative response profiles along the single axis measured with the sDMG detector were found to have good agreement between experiment and simulation with the position of the Bragg peak determined to fall within 0.2 mm or 1.1% of the range in the detector for the two cases. The energy of the beam incident on the detector was found to vary less than 1% between experiment and simulation. The beam energy incident on the phantom was determined to be (280.9 ± 0.8) MeV/u from the experimental and (280.9 ± 0.2) MeV/u from the simulated profiles. These values coincide with the expected energy of 281 MeV/u. The sDMG detector response was studied experimentally and characterized using a Monte Carlo simulation. The sDMG detector was found to accurately determine the
Publisher: Springer Science and Business Media LLC
Date: 14-11-2019
DOI: 10.1007/S13246-019-00808-8
Abstract: Eye Plaque brachytherapy pre-treatment quality assurance (QA) conducted clinically involves an activity verification of in idual seeds via well chamber and does not include a physical measurement of dose-rate of the final assembly. A novel spectroscopic, dose-rate detection system, was evaluated for pre-treatment QA of eye plaque brachytherapy. The system includes a water phantom with sterility management. The system was calibrated using a known-activity I-125 seed, measured at 1 cm in water along the radial axis, compared to TG-43 U1 calculations and verified over a number of distances. A depth dose curve was acquired for a clinical, mixed activity eye plaque and two 'error' plaques. The probe was stepped from a water equivalent source to a detector distance (SDD) of 2.5 to 12 mm along the plaque central axis. The latter measurements aimed to characterise the sensitivity of the system. The calculated and measured single-seed dose-rates agreed to within 0.5 cGy/h from a SDD of 3 mm and above. The clinical plaque showed agreement between measured and treatment planning system (TPS) calculated dose-rates within 2%. Sensitivity testing resulted in a maximum deviation from TPS data of 18%, therefore was able to detect the presence of packing errors. The dose-rate detection system was successfully evaluated for verification of I-125 based eye plaques without compromising sterility, allowing for quick pre-treatment, dose-rate verification of patient-ready plaques. Its agreement with TPS data for the unmodified plaque and its deviation when introducing errors confirms the approach suggested is a viable QA tool.
Publisher: IOP Publishing
Date: 21-01-2019
Publisher: IEEE
Date: 10-2013
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2010
Publisher: IEEE
Date: 10-2013
Publisher: Wiley
Date: 28-03-2020
DOI: 10.1002/MP.14110
Publisher: IOP Publishing
Date: 2017
Publisher: IOP Publishing
Date: 06-12-2013
Publisher: Wiley
Date: 02-2017
DOI: 10.1002/MP.12060
Abstract: Nowadays, there are many different applications that use small fields in radiotherapy treatments. The dosimetry of small radiation fields is not trivial due to the problems associated with lateral disequilibrium and source occlusion and requires reliable quality assurance (QA). Ideally such a QA tool should provide high spatial resolution, minimal beam perturbation and real time fast measurements. Many different types of silicon diode arrays are used for QA in radiotherapy however, their application in small filed dosimetry is limited, in part, due to a lack of spatial resolution. The Center of Medical Radiation Physics (CMRP) has developed a new generation of a monolithic silicon diode array detector that will be useful for small field dosimetry in SRS/SRT. The objective of this study is to characterize a monolithic silicon diode array designed for dosimetry QA in SRS/SRT named DUO that is arranged as two orthogonal 1D arrays with 0.2 mm pitch. DUO is two orthogonal 1D silicon detector arrays in a monolithic crystal. Each orthogonal array contains 253 small pixels with size 0.04 × 0.8 mm The DUO detector shows a dose per pulse dependence of 5% for a range of dose rates from 2.7 × 10 The CMRP's monolithic silicon detector array, DUO, is suitable for SRS/SRT dosimetry and QA because of its very high spatial resolution (0.2 mm) and real time operation.
Publisher: IOP Publishing
Date: 06-2020
DOI: 10.1088/1742-6596/1561/1/012016
Abstract: The vertex detectors for the future hadronic colliders will operate under proton fluencies above 10 16 p/cm 2 . Crystalline Silicon detector technology, up to now, has kept the pace of the increasing fluencies in the LHC era and it is still the prevalent vertex detector material for the present and for the immediate future. Looking ahead in time, an alternative solution for such a detector has to be found because for the future there is no guarantee that Crystalline Silicon will hold this challenge. For this reason the development of hydrogenated amorphous silicon vertex detectors based on 3D-technology have been proposed and the technological solutions in order to build these detectors are described in this paper.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2016
Publisher: Wiley
Date: 30-03-2011
DOI: 10.1118/1.3566067
Abstract: Helical tomotherapy is a complex delivery technique, integrating CT image guidance and intensity modulated radiotherapy in a single system. The integration of the CT detector ring on the gantry not only allows patient position verification but is also often used to perform various QA procedures. This convenience lacks the rigor of a machine-independent QA process. In this article, a Si strip detector, known as the Dose Magnifying Glass (DMG), was used to perform machine-independent QA measurements of the multileaf collimator alignment, leaf open time threshold, and leaf fluence output factor (LFOF). The DMG measurements showed good agreements with EDR2 film for the MLC alignment test while the CT detector agrees well with DMG measurements for leaf open time threshold and LFOF measurements. The leaf open time threshold was found to be approximately 20 ms. The LFOF measured with the DMG agreed within error with the CT detector measured LFOF. The DMG with its 0.2 mm spatial resolution coupled to TERA ASIC allowed real-time high temporal resolution measurements of the tomotherapy leaf movement. In conclusion, DMG was shown to be a suitable tool for machine-independent QA of a tomotherapy unit.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2013
Publisher: Elsevier BV
Date: 09-2014
DOI: 10.1016/J.APRADISO.2014.06.009
Abstract: Circular ion-implanted silicon detector of α-particles with a large, 5-cm(2), sensitive area has been developed. An advantage of the detector is that the detector surface is easily cleanable with chemicals. The hardened surface of the detector shows no signs of deterioration of the spectroscopic and electrical characteristics upon repeated cleaning. The energy resolution along the diameters of the detector was (1.0±0.1)% for the 5.486-MeV α-particles. Detailed tests of the charge collection efficiency and uniformity of the detector entrance window were also performed with a 5.5-MeV He(2+) microbeam.
Publisher: MDPI AG
Date: 04-10-2022
DOI: 10.3390/NANO12193466
Abstract: In this paper, by means of high-resolution photoemission, soft X-ray absorption and atomic force microscopy, we investigate, for the first time, the mechanisms of damaging, induced by neutron source, and recovering (after annealing) of p-i-n detector devices based on hydrogenated amorphous silicon (a-Si:H). This investigation will be performed by mean of high-resolution photoemission, soft X-Ray absorption and atomic force microscopy. Due to dangling bonds, the amorphous silicon is a highly defective material. However, by hydrogenation it is possible to reduce the density of the defect by several orders of magnitude, using hydrogenation and this will allow its usage in radiation detector devices. The investigation of the damage induced by exposure to high energy irradiation and its microscopic origin is fundamental since the amount of defects determine the electronic properties of the a-Si:H. The comparison of the spectroscopic results on bare and irradiated s les shows an increased degree of disorder and a strong reduction of the Si-H bonds after irradiation. After annealing we observe a partial recovering of the Si-H bonds, reducing the disorder in the Si (possibly due to the lowering of the radiation-induced dangling bonds). Moreover, effects in the uppermost coating are also observed by spectroscopies.
Publisher: Elsevier BV
Date: 07-2006
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2010
Publisher: Elsevier BV
Date: 10-2017
DOI: 10.1016/J.EJMP.2017.09.134
Abstract: Cherenkov radiation is generated in optical systems exposed to ionising radiation. In water or plastic devices, if the incident radiation has components with high enough energy (for ex le, electrons or positrons with energy greater than 175keV), Cherenkov radiation will be generated. A scintillator dosimeter that collects optical light, guided by optical fibre, will have Cherenkov radiation generated throughout the length of fibre exposed to the radiation field and compromise the signal. We present a novel algorithm to separate Cherenkov radiation signal that requires only a single probe, provided the radiation source is pulsed, such as a linear accelerator in external beam radiation therapy. We use a slow scintillator (BC-444) that, in a constant beam of radiation, reaches peak light output after 1 microsecond, while the Cherenkov signal is detected nearly instantly. This allows our algorithm to separate the scintillator signal from the Cherenkov signal. The relative beam profile and depth dose of a linear accelerator 6MV X-ray field were reconstructed using the algorithm. The optimisation method improved the fit to the ionisation chamber data and improved the reliability of the measurements. The algorithm was able to remove 74% of the Cherenkov light, at the expense of only 1.5% scintillation light. Further characterisation of the Cherenkov radiation signal has the potential to improve the results and allow this method to be used as a simpler optical fibre dosimeter for quality assurance in external beam therapy.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2006
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2014
Publisher: IEEE
Date: 10-2012
Publisher: Elsevier BV
Date: 06-2021
Publisher: Elsevier BV
Date: 12-2011
Publisher: Springer Science and Business Media LLC
Date: 08-2017
DOI: 10.1007/S11892-017-0903-2
Abstract: This review aimed to examine the latest evidence linking cigarette smoking and cessation to risk of incident diabetes and its complications. Abundant evidence has demonstrated that smoking is associated with increased risk of type 2 diabetes and cardiovascular disease among diabetic patients, while its relationship with microvascular complications is more limited to diabetic nephropathy and neuropathy in type 1 diabetes. In addition, diabetes risk remains high in the short term after smoking cessation, while it reduces gradually in the long term. Risk of cardiovascular complications also substantially decreases after quitting smoking, but results for microvascular complications are not consistent. Smoking is associated with increased risks of incident diabetes in the general population and cardiovascular complications among diabetic patients. Although the short-term post-cessation diabetes risk needs to be acknowledged, this review calls for urgent action to implement population-wide policies and in idual pharmaceutical and lifestyle interventions (if evidence accumulated in future) to aid smoking cessation and prevent diabetes and its complications.
Publisher: Elsevier BV
Date: 2018
DOI: 10.1016/J.BRACHY.2017.08.013
Abstract: With the increase in complexity of brachytherapy treatments, there has been a demand for the development of sophisticated devices for delivery verification. The Centre for Medical Radiation Physics (CMRP), University of Wollongong, has demonstrated the applicability of semiconductor devices to provide cost-effective real-time quality assurance for a wide range of brachytherapy treatment modalities. Semiconductor devices have shown great promise to the future of pretreatment and in vivo quality assurance in a wide range of brachytherapy treatments, from high-dose-rate (HDR) prostate procedures to eye plaque treatments. The aim of this article is to give an insight into several semiconductor-based dosimetry instruments developed by the CMRP. Applications of these instruments are provided for breast and rectal wall in vivo dosimetry in HDR brachytherapy, urethral in vivo dosimetry in prostate low-dose-rate (LDR) brachytherapy, quality assurance of HDR brachytherapy afterloaders, HDR pretreatment plan verification, and real-time verification of LDR and HDR source dwell positions.
Publisher: Springer Science and Business Media LLC
Date: 19-07-2016
DOI: 10.1007/S13246-016-0453-Y
Abstract: Eye plaque brachytherapy has been developed and refined for the last 80 years, demonstrating effective results in the treatment of ocular malignancies. Current dosimetry techniques for eye plaque brachytherapy (such as TLD- and film-based techniques) are time consuming and cannot be used prior to treatment in a sterile environment. The measurement of the expected dose distribution within the eye, prior to insertion within the clinical setting, would be advantageous, as any errors in source loading will lead to an erroneous dose distribution and inferior treatment outcomes. This study investigated the use of spectroscopic dosimetry techniques for real-time quality assurance of I-125 based eye plaques, immediately prior to insertion. A silicon detector based probe, operating in spectroscopy mode was constructed, containing a small (1 mm(3)) silicon detector, mounted within a ceramic holder, all encapsulated within a rubber sheath to prevent water infiltration of the electronics. Preliminary tests of the prototype demonstrated that the depth dose distribution through the central axis of an I-125 based eye plaque may be determined from AAPM Task Group 43 recommendations to a deviation of 6 % at 3 mm depth, 7 % at 5 mm depth, 1 % at 10 mm depth and 13 % at 20 mm depth, with the deviations attributed to the construction of the probe. A new probe design aims to reduce these discrepancies, however the concept of spectroscopic dosimetry shows great promise for use in eye plaque quality assurance in the clinical setting.
Publisher: Wiley
Date: 10-04-2018
DOI: 10.1002/MP.12874
Abstract: The aim of this study was to measure the microdosimetric distributions of a carbon pencil beam scanning (PBS) and passive scattering system as well as to evaluate the relative biological effectiveness (RBE) of different ions, namely Two different silicon microdosimeters with rectangular parallelepiped and cylindrical shaped SVs, both 10 μm in thickness were used in this study. The microdosimeters were connected to low noise electronics which allowed for the detection of lineal energies as low as 0.15 keV/μm in tissue. The silicon microdosimeters provide extremely high spatial resolution and can be used for in-field and out-of-field measurements in both passive scattering and PBS deliveries. The response of the microdosimeters was studied in 290 MeV/u For a 180 MeV/u These SOI microdosimeters with well-defined three-dimensional (3D) SVs have applicability in characterizing heavy ion radiation fields and measuring lineal energy deposition with sub-millimeter spatial resolution. It has been shown that the dose-mean lineal energy increased significantly at the distal part of the BP and SOBP due to very high LET particles. Good agreement was observed for the experimental and simulation results obtained with silicon microdosimeters in
Publisher: IEEE
Date: 09-2009
Publisher: Wiley
Date: 28-01-2020
DOI: 10.1002/MP.14016
Abstract: Dynamic dosimaging is a concept whereby a detector in motion is tracked with magnetic resonance imaging (MRI) to validate the amount and position of dose in a radiation therapy treatment on an MRI-linac. This work takes steps toward the realization of dynamic dosimaging with the novel high resolution silicon array detector: MagicPlate-512 (M512). The performance of the M512 was assessed in a 1.0 T inline MRI-linac, without simultaneous imaging and then during an imaging sequence, both during dosimetry. MR images were acquired to determine the effect of the detector and its components on image quality. Beam profiles were measured using the M512 on the Australian MRI-Linac and a comparison made with Gafchromic EBT3 film to investigate any intrinsic magnetic field effects in the silicon. The M512 has 512 sensitive volumes, each 0.5 × 0.5 × 0.037 mm Good agreement was observed between the M512 and film, with average differences in penumbral width and FWHM of <1 mm in the absence of the imaging sequence. Concurrent imaging widened the penumbra by up to 1.2 mm due to RF noise affecting the detector film profiles were unchanged. Magnetic resonance images were affected by noise, in particular, due to the large amount of aluminum present, as well as from the USB cable, which acted as an antenna. Unfortunately, due to these issues, suitable dynamic dose imaging was not achieved with the current M512 hantom configuration and the MRI-linac. However, progress was made toward achieving this goal for future work. The M512 silicon array detector successfully measured high-resolution beam profiles in agreement with Gafchromic film to within an average of <1 mm on the first MRI-linac in Australia. More effective noise reduction will be required for the achievement of dynamic dosimaging in the future.
Publisher: Elsevier BV
Date: 12-2011
Publisher: Elsevier BV
Date: 06-2003
Publisher: Elsevier BV
Date: 10-2005
Publisher: Elsevier BV
Date: 03-2019
DOI: 10.1016/J.EJMP.2019.02.012
Abstract: This study aims to assess the accuracy of in-vivo source tracking during real-time trans-rectal ultrasound (TRUS) based high dose rate (HDR) prostate brachytherapy (pBT) through Monte Carlo simulations of multiple HDR pBT treatments with a two-dimensional (2D) diode array, the Magic Plate 900 (MP900), embedded below the patient in a carbon-fibre couch. Monte Carlo simulations of source positions representing three separate real-time TRUS based HDR pBT treatments were performed using the Geant4 toolkit. For each source position, an Ir-192 source was simulated inside a voxelized patient geometry. Dose deposited from each source position to the MP900 diodes was used to perform source tracking, and the MP900 calculated position compared to known source positions from the treatment plan. Thresholding techniques were implemented to improve source tracking accuracy with the TRUS probe present. The average three-dimensional source position reconstruction discrepancy was 11.9 ± 2.4 mm and 1.5 ± 0.3 mm with and without the TRUS probe, respectively. Thresholding techniques improved the source position reconstruction discrepancy in the presence of the TRUS probe to 1.8 ± 0.4 mm. Inclusion of the TRUS probe inside the patient negatively affects source tracking accuracy when using the MP900 diode array for HDR pBT verification. Modification of the source tracking algorithm using thresholding techniques improves source tracking in the presence of the TRUS probe, achieving similar accuracy as when the TRUS probe is not present. This study demonstrates that accurate in-vivo source tracking during real-time TRUS based HDR pBT is feasible using the Magic Plate system.
Publisher: Elsevier BV
Date: 12-2011
Publisher: Springer Science and Business Media LLC
Date: 23-05-2016
DOI: 10.1007/S00330-015-3818-9
Abstract: To develop a real-time dose-monitoring system to measure the patient's eye lens dose during neuro-interventional procedures. Radiation dose received at left outer canthus (LOC) and left eyelid (LE) were measured using Metal-Oxide-Semiconductor Field-Effect Transistor dosimeters on 35 patients who underwent diagnostic or cerebral embolization procedures. The radiation dose received at the LOC region was significantly higher than the dose received by the LE. The maximum eye lens dose of 1492 mGy was measured at LOC region for an AVM case, followed by 907 mGy for an aneurysm case and 665 mGy for a diagnostic angiography procedure. Strong correlations (shown as R(2)) were observed between kerma-area-product and measured eye doses (LOC: 0.78, LE: 0.68). Lateral and frontal air-kerma showed strong correlations with measured dose at LOC (AKL: 0.93, AKF: 0.78) and a weak correlation with measured dose at LE. A moderate correlation was observed between fluoroscopic time and dose measured at LE and LOC regions. The MOSkin dose-monitoring system represents a new tool enabling real-time monitoring of eye lens dose during neuro-interventional procedures. This system can provide interventionalists with information needed to adjust the clinical procedure to control the patient's dose. Real-time patient dose monitoring helps interventionalists to monitor doses. Strong correlation was observed between kerma-area-product and measured eye doses. Radiation dose at left outer canthus was higher than at left eyelid.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2020
Publisher: IOP Publishing
Date: 17-10-2014
DOI: 10.1088/0022-3727/59/21/6659
Abstract: HDR BrachyView is a novel in-body dosimetric imaging system for real-time monitoring and verification of the source position in high dose rate (HDR) prostate brachytherapy treatment. It is based on a high-resolution pixelated detector array with a semi-cylindrical multi-pinhole tungsten collimator and is designed to fit inside a compact rectal probe, and is able to resolve the 3D position of the source with a maximum error of 1.5 mm. This paper presents an evaluation of the additional dose that will be delivered to the patient as a result of backscatter radiation from the collimator. Monte Carlo simulations of planar and cylindrical collimators embedded in a tissue-equivalent phantom were performed using Geant4, with an (192)Ir source placed at two different source-collimator distances. The planar configuration was replicated experimentally to validate the simulations, with a MOSkin dosimetry probe used to measure dose at three distances from the collimator. For the cylindrical collimator simulation, backscatter dose enhancement was calculated as a function of axial and azimuthal displacement, and dose distribution maps were generated at three distances from the collimator surface. Although significant backscatter dose enhancement was observed for both geometries immediately adjacent to the collimator, simulations and experiments indicate that backscatter dose is negligible at distances beyond 1 mm from the collimator. Since HDR BrachyView is enclosed within a 1 mm thick tissue-equivalent plastic shell, all backscatter radiation resulting from its use will therefore be absorbed before reaching the rectal wall or other tissues. dosimetry, brachytherapy, HDR.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2004
Publisher: IOP Publishing
Date: 05-06-2014
Publisher: IOP Publishing
Date: 07-2016
Publisher: Wiley
Date: 19-11-2015
DOI: 10.1118/1.4935866
Abstract: This paper presents initial experimental results from a prototype of high dose rate (HDR) BrachyView, a novel in-body source tracking system for HDR brachytherapy based on a multipinhole tungsten collimator and a high resolution pixellated silicon detector array. The probe and its associated position estimation algorithms are validated and a comprehensive evaluation of the accuracy of its position estimation capabilities is presented. The HDR brachytherapy source is moved through a sequence of positions in a prostate phantom, for various displacements in x, y, and z. For each position, multiple image acquisitions are performed, and source positions are reconstructed. Error estimates in each dimension are calculated at each source position and combined to calculate overall positioning errors. Gafchromic film is used to validate the accuracy of source placement within the phantom. More than 90% of evaluated source positions were estimated with an error of less than one millimeter, with the worst-case error being 1.3 mm. Experimental results were in close agreement with previously published Monte Carlo simulation results. The prototype of HDR BrachyView demonstrates a satisfactory level of accuracy in its source position estimation, and additional improvements are achievable with further refinement of HDR BrachyView's image processing algorithms.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 2019
Publisher: Elsevier BV
Date: 11-2019
Publisher: International Union of Crystallography (IUCr)
Date: 24-04-2018
DOI: 10.1107/S1600577518003016
Abstract: Cancer is one of the leading causes of death worldwide. External beam radiation therapy is one of the most important modalities for the treatment of cancers. Synchrotron microbeam radiation therapy (MRT) is a novel pre-clinical therapy that uses highly spatially fractionated X-ray beams to target tumours, allowing doses much higher than conventional radiotherapies to be delivered. A dosimeter with a high spatial resolution is required to provide the appropriate quality assurance for MRT. This work presents a plastic scintillator fibre optic dosimeter with a one-dimensional spatial resolution of 20 µm, an improvement on the dosimeter with a resolution of 50 µm that was demonstrated in previous work. The ability of this probe to resolve microbeams of width 50 µm has been demonstrated. The major limitations of this method were identified, most notably the low-light signal resulting from the small sensitive volume, which made valley dose measurements very challenging. A titanium-based reflective paint was used as a coating on the probe to improve the light collection, but a possible effect of the high- Z material on the probes water-equivalence has been identified. The effect of the reflective paint was a 28.5 ± 4.6% increase in the total light collected it did not affect the shape of the depth-dose profile, nor did it explain an over-response observed when used to probe at low depths, when compared with an ionization chamber. With improvements to the data acquisition, this probe design has the potential to provide a water-equivalent, inexpensive dosimetry tool for MRT.
Publisher: Elsevier BV
Date: 11-2017
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 08-2010
Publisher: Informa UK Limited
Date: 10-08-2005
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 06-2004
Publisher: IOP Publishing
Date: 23-04-2021
Abstract: Proton therapy has a distinct dosimetric advantage over conventional photon therapy due to its Bragg peak profile. This allows greater accuracy in dose delivery and dose conformation to the target, however it requires greater precision in setup, delivery and for quality assurance (QA) procedures. The AAPM TG 224 report recommends daily range and spot position checks with tolerance on the order of a millimetre. Daily QA systems must therefore be efficient for daily use and be capable of sub-millimetre precision however few suitable commercial systems are available. In this work, a compact, real-time daily QA system is optimised and characterised for proton range verification using an ad-hoc Geant4 simulation. The system is comprised of a monolithic silicon diode array detector embedded in a perspex phantom. The detector is orientated at an angular offset to the incident proton beam to allow range in perspex to be determined for flat proton fields. The accuracy of the system for proton range in perspex measurements was experimentally evaluated over the full range of clinical proton energies. The mean R 100 , R 90 and R 80 ranges measured with the system were accurate within ±0.6 mm of simulated ranges in a perspex phantom for all energies assessed. This system allows real-time read-out of in idual detector channels also making it appropriate for temporal beam delivery diagnostics and for spot position monitoring along one axis. The system presented provides a suitable, economical and efficient alternative for daily QA in proton therapy.
Publisher: IOP Publishing
Date: 11-04-2016
Publisher: IOP Publishing
Date: 17-09-2015
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 12-2012
Publisher: IEEE
Date: 2007
Publisher: Wiley
Date: 12-07-2018
DOI: 10.1002/ACM2.12414
Publisher: Springer Science and Business Media LLC
Date: 27-11-2019
DOI: 10.1038/S41598-019-53991-9
Abstract: Microbeam Radiation Therapy (MRT) is an emerging cancer treatment modality characterised by the use of high-intensity synchrotron-generated x-rays, spatially fractionated by a multi-slit collimator (MSC), to ablate target tumours. The implementation of an accurate treatment planning system, coupled with simulation tools that allow for independent verification of calculated dose distributions are required to ensure optimal treatment outcomes via reliable dose delivery. In this article we present data from the first Geant4 Monte Carlo radiation transport model of the Imaging and Medical Beamline at the Australian Synchrotron. We have developed the model for use as an independent verification tool for experiments in one of three MRT delivery rooms and therefore compare simulation results with equivalent experimental data. The normalised x-ray spectra produced by the Geant4 model and a previously validated analytical model, SPEC, showed very good agreement using wiggler magnetic field strengths of 2 and 3 T. However, the validity of absolute photon flux at the plane of the Phase Space File (PSF) for a fixed number of simulated electrons was unable to be established. This work shows a possible limitation of the G 4 SynchrotronRadiation process to model synchrotron radiation when using a variable magnetic field. To account for this limitation, experimentally derived normalisation factors for each wiggler field strength determined under reference conditions were implemented. Experimentally measured broadbeam and microbeam dose distributions within a Gammex RMI457 Solid Water ® phantom were compared to simulated distributions generated by the Geant4 model. Simulated and measured broadbeam dose distributions agreed within 3% for all investigated configurations and measured depths. Agreement between the simulated and measured microbeam dose distributions agreed within 5% for all investigated configurations and measured depths.
Publisher: Elsevier BV
Date: 05-2011
Publisher: Elsevier BV
Date: 2016
Publisher: Elsevier BV
Date: 12-2014
Publisher: Elsevier BV
Date: 11-2017
DOI: 10.1016/J.EJMP.2017.10.017
Abstract: To investigate the effect on surface dose, as a function of different field sizes and distances from the solid water phantom to transmission detector (D The influence of operating the MP512T in transmission mode on the surface dose of a phantom for SSD 100cm was evaluated by using a Markus IC. The MP512T was fixed to an adjustable stand holder and was positioned at different D For all D The study demonstrated that positioning the MP512T in air between the Linac head and the phantom produced negligible perturbation of the surface dose for D
Start Date: 2011
End Date: 12-2014
Amount: $300,000.00
Funder: Australian Research Council
View Funded ActivityStart Date: 2017
End Date: 12-2020
Amount: $357,000.00
Funder: Australian Research Council
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End Date: 12-2025
Amount: $500,983.00
Funder: Australian Research Council
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