ORCID Profile
0000-0001-8306-7742
Current Organisations
University of Western Australia
,
The University of Newcastle
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Publisher: Bentham Science Publishers Ltd.
Date: 19-03-2009
Publisher: Walter de Gruyter GmbH
Date: 07-2008
Abstract: Copper-64 ( t ½ = 12.7 h) is a promising cancer treatment radiotherapy agent and combines positron emission tomography (PET). It was produced utilizing the 64 Ni(p,n) 64 Cu nuclear reaction channel. Natural nickel was electroplated successfully, 48 μm thick, onto a gold-coated copper backing slab. Bombardment of nickel plated target was performed with 16 MeV protons at a current of 200 μA. Copper-64 together with copper-61 was separated from Ni and other non-isotopic impurities by ion exchange chromatography. The method of separation of radiocopper has been improved.
Publisher: Springer Science and Business Media LLC
Date: 31-05-2014
DOI: 10.1007/S11517-014-1161-Y
Abstract: Using an amorphous silicon (a-Si) EPID for transit dosimetry requires detailed characterization of its dosimetric response in a variety of conditions. In this study, a measurement-based model was developed to calibrate an a-Si EPID response to dose for transit dosimetry by comparison with a reference ionization chamber. The ionization chamber reference depth and the required additional buildup thickness for electronic portal imaging devices (EPID) transit dosimetry were determined. The combined effects of changes in radiation field size, phantom thickness, and the off-axis distance on EPID transit dosimetry were characterized. The effect of scattered radiation on out-of-field response was investigated for different field sizes and phantom thicknesses by evaluation of the differences in image profiles and in-water measured profiles. An algorithm was developed to automatically apply these corrections to EPID images based on the user-specified field size and phantom thickness. The average phantom thickness and an effective field size were used for IMRT fields, and images were acquired in cine mode in the presence of an anthropomorphic phantom. The effective field size was defined as the percentage of the jaw-defined field that was involved during the delivery. Nine head and neck dynamic IMRT fields were tested by comparison with a MatriXX two-dimensional array dosimeter using the Gamma (3%, 3 mm) evaluation. A depth of 1.5 cm was selected as the ionization chamber reference depth. An additional 2.2 mm of copper buildup was added to the EPID. Comparison of EPID and MatriXX dose images for the tested fields showed that using a 10% threshold, the average number of points with Gamma index <1 was 96.5%. The agreement in the out-of field area was shown by selection of a 2% threshold which on average resulted in 94.8% of points with a Gamma index <1. The suggested method is less complicated than previously reported techniques and can be used for all a-Si EPIDs regardless of the manufacturer.
Publisher: Wiley
Date: 28-04-2010
DOI: 10.1118/1.3369445
Abstract: Amorphous silicon EPIDs have been used for planar dose verification in IMRT treatments for many years. The support arm used to attach some types of EPIDs to linear accelerators can introduce inaccuracies to dosimetry measurements due to the presence of metallic parts in their structures. It is demonstrated that this uncertainty may be as large as approximately 6% of maximum image signal for large fields. In this study, a method has been described to quantify, model and correct for the effect of backscattered radiation from the EPID support arm (E-Arm type, Varian Medical Systems). Measurements of a support arm backscatter kernel were made using several 1 x 1 cm2 6 MV pencil beam irradiations at a s le of positions over the sensitive area of the EPID in standard clinical setup and repeated with the EPID removed from the support arm but at the same positions. A curve-fit to the subtraction of EPID response obtained on and off the arm was used to define the backscatter kernel. The measured kernel was compared with a backscatter kernel obtained by Monte Carlo simulations with EGS/BEAM code. A backscatter dose prediction using the measured backscatter kernel was added to an existing EPID dose prediction model. The improvement in the agreement of the modified model predictions with EPID measurements for a number of open fields and IMRT beams were investigated by comparison to the original model results. Considering all functions tested to find the best functional fit to the data points, a broad Gaussian curve proved to be the optimum fit to the backscatter data. The best fit through the Monte Carlo simulated backscatter kernel was also found to be a Gaussian curve. The maximum decrease in normalized root mean squared deviation of the measured and modeled EPID image profiles for open fields was 13.7% for a 15 x 15 cm2 field with no decrease observed for a 3 x 3 cm2 (the smallest) field as it was not affected by the arm backscatter. Gamma evaluation (2%, 2 mm criteria) showed the improvement in agreement between the model and measurement results when the backscatter was incorporated. The average increase in Gamma pass rate was 2% for head and neck and 1.3% for prostate IMRT fields investigated in this study. The application of the backscatter kernel determined in this study improved the accuracy of dosimetry using a Varian EPID with E-arm for open fields of different sizes: Eight head and neck and seven prostate IMRT fields. Further improvement in the agreement between the model predictions and EPID measurements requires more sophisticated modeling of the backscatter.
Publisher: IOP Publishing
Date: 07-01-2022
Abstract: Objectiv e. The objective of this study was to separately quantify the stability of the megavoltage imager (MVI) and radiation head of an Elekta Unity MRL, throughout full gantry rotation. Approach . A ball-bearing (BB) phantom was attached to the radiation head of the Unity, while a single BB was placed at isocentre. Images were acquired during rotation, using the MVI. These images were processed using an in-house developed MATLAB program to reduce the errors resulted by noise, and the positions of the BBs in the images were analysed to extract MVI and radiation head sag data. Main results . The results returned by this method showed reproducibility, with a mean standard deviation of 7 μ m for the position of BBs across all gantry angles. The radiation head was found to sag throughout rotation, with a maximum course of movement of 0.59 mm. The sag pattern was stable over a period greater than a year but showed some dependence on gantry rotation direction. Significance . As MRL is a relatively new system, it is promising to have data supporting the high level of precision on one Elekta Unity machine. Isolating and quantifying the sources of uncertainty in radiation delivery may allow more sophisticated analysis of how the system performance may be improved.
Publisher: MDPI AG
Date: 08-10-2023
Publisher: Springer Science and Business Media LLC
Date: 08-09-2022
DOI: 10.1186/S13014-022-02123-1
Abstract: The CyberKnife Xsight lung-tracking system (XLTS) provides an alternative to fiducial-based target-tracking systems (FTTS) for non-small-cell lung cancer (NSCLC) patients without invasive fiducial insertion procedures. This study provides a method for 3D independent dosimetric verification of the accuracy of the FTTS compared to the XLTS without relying on log-files generated by the CyberKnife system. A respiratory motion trace was taken from a 4D-CT of a real lung cancer patient and applied to a modified QUASAR™ respiratory motion phantom. A novel approach to 3D dosimetry was developed using Gafchromic EBT3 film, allowing the 3D dose distribution delivered to the moving phantom to be reconstructed. Treatments were planned using the recommended margins for one and three fiducial markers and XLTS 2-view, 1-view and 0-view target-tracking modalities. The dose delivery accuracy was analysed by comparing the reconstructed dose distributions to the planned dose distributions using gamma index analysis. For the 3%/2 mm gamma criterion, gamma passing rates up to 99.37% were observed for the static deliveries. The 3-fiducial and 1-fiducial-based deliveries exhibited passing rates of 93.74% and 97.82%, respectively, in the absence of target rotation. When target rotation was considered, the passing rate for 1-fiducial tracking degraded to 91.24%. The passing rates observed for XLTS 2-view, 1-view and 0-view target-tracking were 92.78%, 96.22% and 76.08%, respectively. Except for the XLTS 0-view, the dosimetric accuracy of the XLTS was comparable to the FTTS under equivalent treatment conditions. This study gives us further confidence in the CyberKnife XLTS and FTTS systems.
Publisher: Wiley
Date: 03-04-2019
DOI: 10.1002/JMRS.331
Publisher: Elsevier BV
Date: 12-2006
DOI: 10.1016/J.APRADISO.2005.11.012
Abstract: In this article, production methods and applications of copper radionuclides are overviewed with special attention toward (61)Cu, due to its interesting nuclear properties. Selection of production parameters for (61)Cu including: appropriate nuclear reaction, proton beam energy, target thickness and targetry method are discussed for NRCAM 30MeV medical cyclotron. (64)Zn(p,alpha)(61)Cu was selected as the best reaction and (61)Cu was produced by 22MeV proton bombardment of a 80 microm thick natural zinc target. After 180microAh irradiation, the resultant activity of (61)Cu was 6.006Ci (12.015mCi/microAh). The chemical separation method was easy, quick and efficient (>95%) and yielded a no carrier added product with high chemical and radionuclidic purity (>99%). Detailed comparison with previous production methods confirms that our results are superior to other reports published to date.
Publisher: Wiley
Date: 24-09-2012
DOI: 10.1118/1.4752207
Abstract: In advanced radiotherapy treatments such as intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT), verification of the performance of the multileaf collimator (MLC) is an essential part of the linac QA program. The purpose of this study is to use the existing measurement methods for geometric QA of the MLCs and extend them to more comprehensive evaluation techniques, and to develop dedicated robust algorithms to quantitatively investigate the MLC performance in a fast, accurate, and efficient manner. The behavior of leaves was investigated in the step-and-shoot mode by the analysis of integrated electronic portal imaging device (EPID) images acquired during picket fence tests at fixed gantry angles and arc delivery. The MLC was also studied in dynamic mode by the analysis of cine EPID images of a sliding gap pattern delivered in a variety of conditions including different leaf speeds, deliveries at fixed gantry angles or in arc mode, and changing the direction of leaf motion. The accuracy of the method was tested by detection of the intentionally inserted errors in the delivery patterns. The algorithm developed for the picket fence analysis was able to find each in idual leaf position, gap width, and leaf bank skewness in addition to the deviations from expected leaf positions with respect to the beam central axis with sub-pixel accuracy. For the three tested linacs over a period of 5 months, the maximum change in the gap width was 0.5 mm, the maximum deviation from the expected leaf positions was 0.1 mm and the MLC skewness was up to 0.2°. The algorithm developed for the sliding gap analysis could determine the velocity and acceleration∕deceleration of each in idual leaf as well as the gap width. There was a slight decrease in the accuracy of leaf performance with increasing leaf speeds. The analysis results were presented through several graphs. The accuracy of the method was assessed as 0.01 mm for both the gap size and peak position determination. This study provides fast, easy, and accurate test methods for routine QA of the MLC performance and helps in faster troubleshooting of MLC problems in both IMRT and VMAT treatments.
Publisher: Wiley
Date: 06-2011
DOI: 10.1118/1.3613021
Publisher: Pleiades Publishing Ltd
Date: 12-2009
Publisher: Frontiers Media SA
Date: 03-11-2022
Abstract: Current accepted linac Quality Assurance (QA) guidelines used for Volumetric Modulated Arc Therapy (VMAT) suggest a mechanical isocentre tolerance level of 1 mm. However, this tolerance level has not been well-established for the specific case of small field stereotactic VMAT. This study aims to evaluate the clinical impact of mechanical uncertainty on this treatment modality by modelling systematic gantry sag derived isocentre variance in the Treatment Planning System (TPS). A previously reported dataset of gantry sag values in the literature served as a starting point for this study. Using an in-house developed VMAT arc splitting algorithm, isocentre shifts were applied at a Control Point (CP) level to DICOM-RT treatment plans. Dose distributions for varying isocentre shift magnitudes were calculated for a set of 29 stereotactic VMAT plans using the Eclipse Acuros XB dose algorithm. These plans had a range of Planning Target Volume (PTV) sizes. A quantitative comparison of each plan was conducted by evaluating five Dose Volume Histogram (DVH)-derived plan quality metrics. All metrics exhibited a deterioration in plan quality with increasing magnitudes of isocentre shift. At small PTV sizes, these effects were lified, exhibiting significant changes at 1 mm of average shift when typical targets and tolerances were considered. For plans with PTVs between 0 and 5 cm 3 , a 1 mm shift reduced PTV coverage by 6.6 ± 2.2% and caused a 12.1 ± 3.8% deterioration in the conformity index. Based on the results of this study, the prevalent tolerance of 1 mm may not be suitable for treatments of small PTVs with small fields. In contrast to commonly accepted values, an absolute mechanical isocentre of 0.5 mm with action level at 0.75 mm is recommended for stereotactic VMAT of PTV sizes below 10 cm 3 .
Publisher: MDPI AG
Date: 2008
Publisher: Elsevier BV
Date: 04-2023
Publisher: MDPI AG
Date: 2008
Publisher: Elsevier BV
Date: 05-2004
Publisher: Springer Science and Business Media LLC
Date: 03-2009
Publisher: British Institute of Radiology
Date: 24-10-2023
DOI: 10.1259/BJR.20221178
Publisher: Springer Science and Business Media LLC
Date: 23-03-2023
DOI: 10.1007/S13246-023-01243-6
Abstract: Intraoperative radiotherapy (IORT) is a specialised subset of radiotherapy, where a high radiation dose is delivered to a surgically exposed tumour bed in order to eradicate any remaining cancer cells. The aim of this study was to examine the dose characteristics of the Zeiss Intrabeam IORT device which provides near-isotropic emission of up to 50 kV X-rays. The EGSnrc Monte Carlo (MC) code system was used to simulate the device and percentage depth dose (PDD) data measured with a soft X-ray parallel-plate ionisation chamber were used for model verification. The model provided energy spectra, isodose curves and mean photon energies. In addition, EBT3 Gafchromic film was used to verify the MC model by examining PDDs and 2D dose distributions for various applicators. The differences between MC model and ionisation chamber measurements were within 3% for most points, with a maximum deviation of ~ 9%. Most of the simulated PDD points were within 5% of the film-measured data, with a maximum deviation of ~ 10%. The mean energy of the bare probe was found to be 21.19 keV. The mean photon energy from applicators ranged from 29.00 to 30.85 keV. Results of this study may be useful for future work on creating a system for treatment planning.
Publisher: Wiley
Date: 2014
Publisher: Wiley
Date: 07-2010
DOI: 10.1118/1.3476219
Publisher: Springer Science and Business Media LLC
Date: 05-2005
Publisher: Public Library of Science (PLoS)
Date: 05-05-2022
DOI: 10.1371/JOURNAL.PONE.0267741
Abstract: In radiotherapy , the presence of air gaps near a tumour can lead to underdose to the tumour. In this study, the impact of air gaps on dose to the surface was evaluated. 3D-printing was used to construct a Eurosil-4 Pink bolus customised to the patient and its dosimetric properties were compared with that of Paraffin wax bolus. Surface dose was measured for flat sheets of Eurosil-4 Pink bolus with different thicknesses. Different air gap thicknesses were inserted between the bolus and the surface, and dose was measured for each air gap using 10 cm × 10 cm fields. This was repeated with the effective field size calculated from the patient plan. Surface dose was measured for varying angles of incidence. A customised chest phantom was used to compare dose for two customised Eurosil-4 Pink boluses, and commonly used Paraffin wax bolus. The surface dose was found to be highest for 1.1 cm thick bolus. The decrease in surface dose for the Eurosil-4 Pink bolus was minimal for the 10 cm × 10 cm field, but higher for the effective field size and larger angles of incidence. For instance, the dose was reduced by 6.2% as a result of 1 cm air gap for the effective field size and 60 degree angle of incidence. The doses measured using Gafchromic film under the customised Eurosil-4 Pink boluses were similar to that of the Paraffin wax bolus, and higher than prescribed dose. The impact of air gaps can be significant for small field sizes and oblique beams. A customised Eurosil-4 Pink bolus has promising physical and dosimetric properties to ensure sufficient dose to the tumour, even for treatments where larger impact of air gaps is suspected.
Publisher: IOP Publishing
Date: 12-12-2013
DOI: 10.1088/0031-9155/59/1/61
Abstract: A new tool has been developed to verify the trajectory of dynamic multileaf collimators (MLCs) used in advanced radiotherapy techniques using only the information provided by the electronic portal imaging devices (EPID) measured image frames. The prescribed leaf positions are res led to a higher resolution in a pre-processing stage to improve the verification precision. Measured MLC positions are extracted from the EPID frames using a template matching method. A cosine similarity metric is then applied to synchronise measured and planned leaf positions for comparison. Three additional comparison functions were incorporated to ensure robust synchronisation. The MLC leaf trajectory error detection was simulated for both intensity modulated radiation therapy (IMRT) (prostate) and volumetric modulated arc therapy (VMAT) (head-and-neck) deliveries with anthropomorphic phantoms in the beam. The overall accuracy for MLC positions automatically extracted from EPID image frames was approximately 0.5 mm. The MLC leaf trajectory verification system can detect leaf position errors during IMRT and VMAT with a tolerance of 3.5 mm within 1 s.
Publisher: Wiley
Date: 06-2011
DOI: 10.1118/1.3612160
Publisher: Wiley
Date: 07-2010
DOI: 10.1118/1.3476156
Publisher: Springer Science and Business Media LLC
Date: 13-08-2007
Publisher: Springer Science and Business Media LLC
Date: 26-11-2014
Publisher: Frontiers Media SA
Date: 11-2021
Abstract: Metastatic Prostate Cancer (mPCa) is associated with a poor patient prognosis. mPCa spreads throughout the body, often to bones, with spatial and temporal variations that make the clinical management of the disease difficult. The evolution of the disease leads to spatial heterogeneity that is extremely difficult to characterise with solid biopsies. Imaging provides the opportunity to quantify disease spread. Advanced image analytics methods, including radiomics, offer the opportunity to characterise heterogeneity beyond what can be achieved with simple assessment. Radiomics analysis has the potential to yield useful quantitative imaging biomarkers that can improve the early detection of mPCa, predict disease progression, assess response, and potentially inform the choice of treatment procedures. Traditional radiomics analysis involves modelling with hand-crafted features designed using significant domain knowledge. On the other hand, artificial intelligence techniques such as deep learning can facilitate end-to-end automated feature extraction and model generation with minimal human intervention. Radiomics models have the potential to become vital pieces in the oncology workflow, however, the current limitations of the field, such as limited reproducibility, are impeding their translation into clinical practice. This review provides an overview of the radiomics methodology, detailing critical aspects affecting the reproducibility of features, and providing ex les of how artificial intelligence techniques can be incorporated into the workflow. The current landscape of publications utilising radiomics methods in the assessment and treatment of mPCa are surveyed and reviewed. Associated studies have incorporated information from multiple imaging modalities, including bone scintigraphy, CT, PET with varying tracers, multiparametric MRI together with clinical covariates, spanning the prediction of progression through to overall survival in varying cohorts. The methodological quality of each study is quantified using the radiomics quality score. Multiple deficits were identified, with the lack of prospective design and external validation highlighted as major impediments to clinical translation. These results inform some recommendations for future directions of the field.
Publisher: Frontiers Media SA
Date: 04-07-2023
DOI: 10.3389/FONC.2023.1181450
Abstract: Age is a risk factor for both cardiovascular disease and cancer, and as such radiation oncologists frequently see a number of patients with cardiac implantable electronic devices (CIEDs) receiving proton therapy (PT). CIED malfunctions induced by PT are nonnegligible and can occur in both passive scattering and pencil beam scanning modes. In the absence of an evidence-based protocol, the authors emphasise that this patient cohort should be managed differently to electron- and photon- external beam radiation therapy (EBRT) patients due to distinct properties of proton beams. Given the lack of a PT-specific guideline for managing this cohort and limited studies on this important topic the process was initiated by evaluating all PT-related CIED malfunctions to provide a baseline for future reporting and research. In this review, different modes of PT and their interactions with a variety of CIEDs and pacing leads are discussed. Effects of PT on CIEDs were classified into a variety of hardware and software malfunctions. Apart from secondary neutrons, cumulative radiation dose, dose rate, CIED model/manufacturer, distance from CIED to proton field, and materials used in CIEDs acing leads were all evaluated to determine the probability of malfunctions. The importance of proton beam arrangements is highlighted in this study. Manufacturers should specify recommended dose limits for patients undergoing PT. The establishment of an international multidisciplinary team dedicated to CIED-bearing patients receiving PT may be beneficial.
Publisher: Elsevier BV
Date: 03-2006
DOI: 10.1016/J.APRADISO.2005.08.002
Abstract: Due to the interesting anti-proliferative properties of copper-thiosemicarbazone complexes, the production of a (61)Cu-labeled thiosemicarbazone, i.e. 2-acetylpyridine thiosemicarbazone (APTS) was investigated. Copper-61 (T(1/2)=3.33 h) was produced via the (64)Zn(p,alpha)(61)Cu nuclear reaction using a natural zinc target irradiated with 22 MeV protons for 500 microAh. The (61)Cu was separated from the irradiated target material by a two-step method and converted to acetate this yielded a final activity of 222 GBq (6.0 Ci), with a radiochemical yield of >95%. The (61)Cu-acetate was mixed with 2-acetylpyridine thiosemicarbazone for 30 min at room temperature to yield [(61)Cu]APTS with a radiochemical yield of more than 80%. Colorimetric methods showed that residual chemical impurities in the product were below the accepted limits. Radio thin layer chromatography (RTLC) showed a radiochemical purity of more than 99% after C(18) column chromatography. A specific activity of about 370-740 MBq/mmol (10-20 Ci/mmol) was obtained. The stability of the final product was checked in the absence and presence of human serum at 37 degrees C for up to 3 h. The partition coefficient of the final complex was also determined.
Publisher: Informa UK Limited
Date: 07-04-2021
Publisher: Springer Science and Business Media LLC
Date: 11-08-2023
DOI: 10.1007/S00259-023-06371-5
Abstract: The O-(2-[ 18 F]-fluoroethyl)- l -tyrosine (FET) PET in Glioblastoma (FIG) trial is an Australian prospective, multi-centre study evaluating FET PET for glioblastoma patient management. FET PET imaging timepoints are pre-chemoradiotherapy (FET1), 1-month post-chemoradiotherapy (FET2), and at suspected progression (FET3). Before participant recruitment, site nuclear medicine physicians (NMPs) underwent credentialing of FET PET delineation and image interpretation. Sites were required to complete contouring and dynamic analysis by ≥ 2 NMPs on benchmarking cases ( n = 6) assessing biological tumour volume (BTV) delineation (3 × FET1) and image interpretation (3 × FET3). Data was reviewed by experts and violations noted. BTV definition includes tumour-to-background ratio (TBR) threshold of 1.6 with crescent-shaped background contour in the contralateral normal brain. Recurrence seudoprogression interpretation (FET3) required assessment of maximum TBR (TBR max ), dynamic analysis (time activity curve [TAC] type, time to peak), and qualitative assessment. Intraclass correlation coefficient (ICC) assessed volume agreement, coefficient of variation (CoV) compared maximum/mean TBR (TBR max /TBR mean ) across cases, and pairwise analysis assessed spatial (Dice similarity coefficient [DSC]) and boundary agreement (Hausdorff distance [HD], mean absolute surface distance [MASD]). Data was accrued from 21 NMPs (10 centres, n ≥ 2 each) and 20 underwent review. The initial pass rate was 93/119 (78.2%) and 27/30 requested resubmissions were completed. Violations were found in 25/72 (34.7% 13/12 minor/major) of FET1 and 22/74 (29.7% 14/8 minor/major) of FET3 reports. The primary reasons for resubmission were as follows: BTV over-contour (15/30, 50.0%), background placement (8/30, 26.7%), TAC classification (9/30, 30.0%), and image interpretation (7/30, 23.3%). CoV median and range for BTV, TBR max , and TBR mean were 21.53% (12.00–30.10%), 5.89% (5.01–6.68%), and 5.01% (3.37–6.34%), respectively. BTV agreement was moderate to excellent (ICC = 0.82 95% CI, 0.63–0.97) with good spatial (DSC = 0.84 ± 0.09) and boundary (HD = 15.78 ± 8.30 mm MASD = 1.47 ± 1.36 mm) agreement. The FIG study credentialing program has increased expertise across study sites. TBR max and TBR mean were robust, with considerable variability in BTV delineation and image interpretation observed.
Publisher: Wiley
Date: 04-2019
DOI: 10.1002/MP.13491
Abstract: Mechanical sag in the radiotherapy linear accelerator gantry and multi-leaf collimator (MLC) carriage effectively causes systematic deviations in the isocenter with respect to gantry angle. To minimize the impact of this error on treatment, a tolerance value of a 1-mm mechanical isocenter shift is commonly accepted for intensity-modulated radiation therapy quality assurance (QA). However, this tolerance value has not been firmly established for volumetric modulated arc therapy (VMAT) treatments. The purpose of this study is therefore to evaluate the impact of gantry and MLC carriage sag on VMAT clinical performance. A published dataset of Elekta and Varian sag measurements served as a starting point for the investigation. Typical sag profiles were chosen and modeled as continuous isocenter deviations in three dimensions. The data were then incorporated into existing Digital Imaging and Communications in Medicine protocol, extended for radiotherapy plans via a "beam-splitting" algorithm. Three treatment sites were investigated in parallel: head and neck, prostate, and prostate with surrounding lymph nodes. Monte Carlo-simulated dose distributions were obtained for varying magnifications of the modeled sag. The resulting dose distributions, including that for no error, were compared qualitatively and quantitatively, against multiple metrics. The dose-volume histograms (DVHs) for all plans exhibited a decrease in planning target volume (PTV) dose uniformity with increasing sag magnification, whereas dose to organs at risk exhibited no coherent trend. The prostate plan was shown to be the most vulnerable to mechanical sag across all considered metrics. However, all plans with peak isocenter deviation less than 1 mm were well within typical cutoff points for each metric. All avenues of investigation presented substantiate the commonly accepted tolerance value of a 1-mm peak isocenter shift in annual linac QA.
Publisher: IOP Publishing
Date: 31-01-2019
Abstract: The potential for delivering high precision radiotherapy using linear accelerators (linacs) has been improved with the development of digital x-ray electronic portal imaging devices (EPID) for acquiring kilovoltage (kV) cone-beam CT and megavoltage (MV) images for patient positioning. EPIDs have also opened the possibilities of developing novel quality assurance and insight into radiotherapy equipment performance. The aim of this work was to measure the offset of the focal spot position (FSP) of a linac under gantry rotation relative to the collimator axis using an EPID. The focal spot was assumed to be a point source of MV x-ray generation. A special phantom was designed for measurement of FSP as a function of gantry angle on clinical linacs. The phantom was designed for attachment to the gantry head and supporting two tungsten-carbide ball-bearings at two different distances from the focal spot. The methodology was demonstrated on a series of images acquired of the phantom on three Elekta linacs in clinical use with 6 MV flattening-filter-free (FFF) beams. The gantry and collimator were rotated 360° in steps of 30°. For each position an image of the phantom was acquired using the EPID. Each series consisted of 169 EPID images. The images were analysed using in-house developed software. Analyses of the EPID images acquired with 6 MV FFF beams showed that the focal spot motion litudes relative to the collimator axis during gantry rotation in the longitudinal and lateral directions were less than 0.10 mm and 0.50 mm, respectively, for an optimized 6 MV FFF FSP calibrated linac. In a treatment planning system (TPS) the focal spot is assumed to be located on the rotation axis of the collimator at all gantry angles. This work introduces a method for quantifying the actual variation from this assumption in practice.
Publisher: Springer Science and Business Media LLC
Date: 17-10-2023
Publisher: Wiley
Date: 17-06-2011
DOI: 10.1118/1.3597836
Abstract: Verification of the mechanical isocenter position is required as part of comprehensive quality assurance programs for stereotactic radiosurgery/radiotherapy (SRS/SRT) treatments. Several techniques have been proposed for this purpose but each of them has certain drawbacks. In this paper, a new efficient and more comprehensive method using cine-EPID images has been introduced for automatic verification of the isocenter with sufficient accuracy for stereotactic applications. Using a circular collimator fixed to the gantry head to define the field, EPID images of a Winston-Lutz phantom were acquired in cine-imaging mode during 3600 gantry rotations. A robust MATLAB code was developed to analyze the data by finding the center of the field and the center of the ball bearing shadow in each image with sub-pixel accuracy. The distance between these two centers was determined for every image. The method was evaluated by comparison to results of a mechanical pointer and also by detection of a manual shift applied to the phantom position. The repeatability and reproducibility of the method were tested and it was also applied to detect couch and collimator wobble during rotation. The accuracy of the algorithm was 0.03 +/- 0.02 mm. The repeatability was less than 3 pm and the reproducibility was less than 86 microm. The time elapsed for the analysis of more than 100 cine images of Varian aS1000 and aS500 EPIDs were approximately 65 and 20 s, respectively. Processing of images taken in integrated mode took 0.1 s. The output of the analysis software is printable and shows the isocenter shifts as a function of angle in both in-plane and cross-plane directions. It gives warning messages where the shifts exceed the criteria for SRS/SRT and provides useful data for the necessary adjustments in the system including bearing system and/or room lasers. The comprehensive method introduced in this study uses cine-images, is highly accurate, fast, and independent of the observer. It tests all gantry angles and is suitable for pretreatment QA of the isocenter for stereotactic treatments.
Publisher: Springer Science and Business Media LLC
Date: 27-07-2020
Publisher: Wiley
Date: 20-07-2021
DOI: 10.1002/MP.15070
Abstract: The use of three‐dimensional (3D) printing to develop custom phantoms for dosimetric studies in radiotherapy is increasing. The process allows production of phantoms designed to evaluated specific geometries, patients, or patient groups with a defining feature. The ability to print bone‐equivalent phantoms has, however, proved challenging. The purpose of this work was to 3D print a series of three similar spine phantoms containing no surgical implants, implants made of titanium, and implants made of carbon fiber, for future dosimetric and imaging studies. Phantoms were evaluated for (a) tissue and bone equivalence, (b) geometric accuracy compared to design, and (c) similarity to one another. S le blocks of PLA, HIPS, and StoneFil PLA‐concrete with different infill densities were printed to evaluate tissue and bone equivalence. The s les were used to develop CT to physical (PD) and effective relative electron density (RED eff ) conversion curves and define the settings for printing the phantoms. CT scans of the printed phantoms were obtained to assess the geometry and densities achieved. Mean distance to agreement (MDA) and DICE coefficient (DSC) values were calculated between contours defining the different materials, obtained from design and like phantom modules. HU values were used to determine PD and RED eff and subsequently evaluate tissue and bone equivalence. S le objects showed linear relationships between HU and both PD and RED eff for both PLA and StoneFil. The PD and RED eff of the objects calculated using clinical CT conversion curves were not accurate and custom conversion curves were required. PLA printed with 90% infill density was found to have a PD of 1.11 ± 0.03 g.cm −3 and RED eff of 1.04 ± 0.02 and selected for tissue‐ equivalent phantom elements. StoneFil printed with 100% infill density showed a PD of 1.35 ± 0.03 g.cm −3 and RED eff of 1.24 ± 0.04 and was selected for bone‐equivalent elements. Upon evaluation of the final phantoms, the PLA elements displayed PD in the range of 1.10 ± 0.03 g.cm −3 –1.13 ± 0.03 g.cm −3 and RED eff in the range of 1.02 ± 0.03–1.06 ± 0.03. The StoneFil elements showed PD in the range of 1.43 ± 0.04 g.cm −3 –1.46 ± 0.04 g.cm −3 and RED eff in the range of 1.31 ± 0.04–1.33 ± 0.04. The PLA phantom elements were shown to have MDA of ≤1.00 mm and DSC of ≥0.95 compared to design, and ≤0.48 mm and ≥0.91 compared like modules. The StoneFil elements displayed MDA values of ≤0.44 mm and DSC of ≥0.98 compared to design and ≤0.43 mm and ≥0.92 compared like modules. Phantoms which were radiologically equivalent to tissue and bone were produced with a high level of similarity to design and even higher level of similarity of one another. When used in conjunction with the derived CT to PD or RED eff conversion curves they are suitable for evaluating the effects of spinal surgical implants of varying material of construction.
Publisher: Elsevier BV
Date: 06-2008
Publisher: Wiley
Date: 05-2016
Publisher: Elsevier BV
Date: 07-2019
DOI: 10.1016/J.EJMP.2019.05.021
Abstract: The characteristics of the focal spot of the linear accelerator (linac) play a role in determining the resulting dose distribution within the patient, and hence probability of treatment success. A direct measurement of focal spot position is not recommended by AAPM Task Group 142, but factors influenced by focal spot position, such as beam symmetry and isocentre position, are. Traditional methods of measuring focal spot position are time consuming and can only be performed at gantry 0°. The presented method has been proposed using a phantom of novel design to accurately measure the position of the focal spot relative to the collimator's axis of rotation (CAX) at any gantry angle, and to measure the intra-fraction movement of the focal spot relative to the mean position during treatment. The method was reproducible to within 0.012 mm/0.029 mm (mean/max) for the three Varian linacs tested. The focal spot position was shown to deviate from the CAX by up to 0.386 mm during gantry rotation. The focal spot position was more unstable at the start of treatment, with the worst performing linac having an initial displacement of up to 0.15 mm from its mean position before stabilizing to within 0.01 mm after 3 s. The method proposed is a beneficial addition to the quality assurance (QA) schedule of any clinic, allowing quick determination of source position and movement at any gantry angle. Measurement of focal spot allows the possibility of fine-tuning the electron beam steering system to improve the standard of the photon beam and of stereotactic treatments.
Publisher: Springer Science and Business Media LLC
Date: 15-04-2019
Publisher: Springer Science and Business Media LLC
Date: 07-2006
Publisher: IOP Publishing
Date: 16-05-2016
Publisher: IOP Publishing
Date: 20-10-2010
DOI: 10.1088/0031-9155/55/22/003
Abstract: Backscatter from the metallic components in the support arm is one of the sources of inaccuracy in dosimetry with Varian amorphous silicon electronic portal imaging devices (a-Si EPIDs). In this study, the non-uniform arm backscatter is blocked by adding lead sheets between the EPID and an E-type support arm. By comparing the EPID responses on and off the arm, with and without lead and considering the extra weight on the imager, 2 mm of lead was determined as the optimum thickness for both 6 and 18 MV beam energies. The arm backscatter at the central axis with the 2 mm lead in place decreased to 0.1% and 0.2% for the largest field size of 30 × 30 cm(2) using 6 and 18 MV beams, from 2.3% and 1.3% without lead. Changes in the source-to-detector distance (SDD) did not affect the backscatter component more than 1%. The symmetry of the in-plane profiles improved for all field sizes for both beam energies. The addition of lead decreased the contrast-to-noise ratio and resolution by 1.3% and 0.84% for images taken in 6 MV and by 0.5% and 0.38% for those in 18 MV beams. The displacement of the EPID central pixel was measured during a 360° gantry rotation with and without lead which was 1 pixel different. While the backscatter reduces with increasing lead thickness, a 2 mm lead sheet seems sufficient for acceptable dosimetry results without any major degradation to the routine performance of the imager. No increase in patient skin dose was detected.
Publisher: British Institute of Radiology
Date: 07-2015
DOI: 10.1259/BJR.20140581
Publisher: Walter de Gruyter GmbH
Date: 02-2006
DOI: 10.1524/RACT.2006.94.2.113
Abstract: Copper-61 (T 1/2 = 3.33 h) produced via the nat Zn( p , x ) 61 Cu nuclear reaction using natural zinc target, was separated from the irradiated target material by a two-step method developed in our laboratory and was used for the preparation of [ 61 Cu]-pyruvaldehyde- bis (N 4 -methylthiosemicarbazone) ([ 61 Cu]-PTSM) using an in house-made PTSM ligand. An electroplated natural zinc layer on a gold-coated copper backing (zinc and gold layer thicknesses were 80 and 50 μm respectively) was irradiated with 22 MeV protons (22−12 MeV on the target). 61 Cu was separated by a two-step chromatography method using a cation and an anion exchange column which gave satisfactory results. After 180 μA irradiation of the target for 3.2 hours, about 6.006 Ci of 61 Cu 2+ was obtained with a radiochemical separation yield of more than 95% and a radionuclidic purity of more than 99% ( 60 Cu as impurity). Colorimetric methods showed that traces of chemical impurities in the product were below the accepted limits. The solution of [ 61 Cu]-PTSM was prepared with a radiochemical yield of higher than 80%, radiochemical purity of better than 98% and specific activity of about 246 Ci/mmol.
Publisher: Springer Science and Business Media LLC
Date: 08-08-2023
DOI: 10.1007/S00259-023-06382-2
Abstract: This study aimed to (i) validate the Response Evaluation Criteria in PSMA (RECIP 1.0) criteria in a cohort of biochemically recurrent (BCR) prostate cancer (PCa) patients and (ii) determine if this classification could be performed fully automatically using a trained artificial intelligence (AI) model. One hundred ninety-nine patients were imaged with [ 68 Ga]Ga-PSMA-11 PET/CT once at the time of biochemical recurrence and then a second time a median of 6.0 months later to assess disease progression. Standard-of-care treatments were administered to patients in the interim. Whole-body tumour volume was quantified semi-automatically (TTV man ) in all patients and using a novel AI method (TTV AI ) in a subset ( n = 74, the remainder were used in the training process of the model). Patients were classified as having progressive disease (RECIP-PD), or non-progressive disease (non RECIP-PD). Association of RECIP classifications with patient overall survival (OS) was assessed using the Kaplan-Meier method with the log rank test and univariate Cox regression analysis with derivation of hazard ratios (HRs). Concordance of manual and AI response classifications was evaluated using the Cohen’s kappa statistic. Twenty-six patients (26/199 = 13.1%) presented with RECIP-PD according to semi-automated delineations, which was associated with a significantly lower survival probability (log rank p 0.005) and higher risk of death (HR = 3.78 (1.96–7.28), p 0.005). Twelve patients (12/74 = 16.2%) presented with RECIP-PD according to AI-based segmentations, which was also associated with a significantly lower survival (log rank p = 0.013) and higher risk of death (HR = 3.75 (1.23–11.47), p = 0.02). Overall, semi-automated and AI-based RECIP classifications were in fair agreement (Cohen’s k = 0.31). RECIP 1.0 was demonstrated to be prognostic in a BCR PCa population and is robust to two different segmentation methods, including a novel AI-based method. RECIP 1.0 can be used to assess disease progression in PCa patients with less advanced disease. This study was registered with the Australian New Zealand Clinical Trials Registry (ACTRN12615000608561) on 11 June 2015.
Publisher: Wiley
Date: 15-05-2022
DOI: 10.1002/ACM2.13652
Abstract: Matching multiple linacs to common baseline data allows patients to be treated, and patient‐specific quality assurance (PSQA) to be completed on any linac. Stereotactic body radiotherapy (SBRT) requires higher levels of accuracy and quality assurance than routine radiotherapy. The achieved linac matching must therefore be evaluated before distributive treatment or PSQA models can be implemented safely. This investigation aimed to propose metrics for defining linacs to be matched for SBRT deliveries, assess 12 linacs against these criteria, and determine if a distributive PSQA model could be implemented by reviewing the rates of false PSQA results. Ten SBRT spine plans were delivered by 12 matched Elekta linacs and measured using one of seven SRS MapCHECK devices. For gamma criteria of (3%, 2 mm), 96.9% of equivalent location detectors, showed a range of gamma ≤ 1.0 and 99.9% showed a standard deviation of ≤ 0.5. For criteria of (3%,1 mm) and (2%,1 mm), these ranges decreased to 92.1% and 80.2% while the standard deviations decreased to 99.3% and 95.7%, respectively. The dose differences showed that 43.6%, 82.7%, and 91.4% of detectors had a dose range of ≤ 3.0%, ≤ 5.0%, and ≤ 6.0%, respectively. Standard deviations of dose differences were 1.5%, 2.5%, and 3.0% for 94.1%, 98.3%, and 99.5% of detectors, respectively. For the fleet of linacs, distributive PSQA yielded false results for 0.0%, 17.7%, and 33.0% of plans, equivalent to 1.2%, 3.5%, and 9.4% of detectors when using gamma criteria of (3%,2 mm), (3%,1 mm), or (2%,1 mm), respectively. These linacs could be considered matched for SBRT treatments and implement a distributive PSQA model when gamma analysis was completed with a criterion of (3%, 2 mm). For stricter criterion of (3%,1 mm) or (2%,1 mm), they did not meet the proposed metrics.
Publisher: Springer Science and Business Media LLC
Date: 08-08-2023
Publisher: Wiley
Date: 31-07-2013
DOI: 10.1118/1.4816384
Abstract: Pretreatment verification of volumetric modulated arc therapy (VMAT) dose delivery with electronic portal imaging device (EPID) uses images integrated over the entire delivery or over large subarcs. This work aims to develop a new method for gantry-angle-resolved verification of VMAT dose delivery using EPID. An EPID dose prediction model was used to calculate EPID images as a function of gantry angle for eight prostate patient deliveries. EPID image frames at 7.5 frames per second were acquired during delivery via a frame-grabber system. The gantry angle for each image was encoded in kV frames which were synchronized to the MV frames. Gamma analysis results as a function of gantry angle were assessed by integrating the frames over 2° subarcs with an angle-to-agreement tolerance of 0.5° about the measured image angle. The model agreed with EPID images integrated over the entire delivery with average Gamma pass-rates at 2%, 2 mm of 99.7% (10% threshold). The accuracy of the kV derived gantry angle for each image was found to be 0.1° (1 SD) using a phantom test. For the gantry-resolved analysis all Gamma pass-rates were greater than 90% at 3%, 3 mm criteria (with only two exceptions), and more than 90% had a 95% pass-rate, with an average of 97.3%. The measured gantry angle lagged behind the predicted angle by a mean of 0.3°±0.3°, with a maximum lag of 1.3°. The method provides a comprehensive and highly efficient pretreatment verification of VMAT delivery using EPID. Dose delivery accuracy is assessed as a function of gantry angle to ensure accurate treatment.
Publisher: Elsevier BV
Date: 02-2015
DOI: 10.1016/J.EJMP.2014.11.002
Abstract: A new tool with the potential to verify and track jaw position during delivery has been developed. The method should be suitable for independent quality assurance for jaw position during jaw tracking dynamic IMRT and VMAT treatments. The jaw detection and tracking algorithm developed consists of five main steps. Firstly, the image is enhanced by removing a normalised predicted EPID image (that does not include the collimator transmission) from each cine EPID image. Then, using a histogram clustering technique a global intensity threshold level was determined. This threshold level was used to classify each pixel of the image as either under the jaws or under the MLC. Additionally, the collimator angle was automatically detected and used to rotate the image to vertical direction. Finally, this rotation allows the jaw positions to be determined using vertical and horizontal projection profiles. Nine IMRT fields (with static jaws) and a single VMAT clinical field (with dynamic jaws) were tested by determining the root mean square difference between planned and detected jaw positions. The test results give a detection accuracy of ±1 mm RMS error for static jaw IMRT treatments and ±1.5 mm RMS error for the dynamic jaw VMAT treatment. This method is designed for quality assurance and verification in modern radiation therapy to detect the position of static jaws or verify the position of tracking jaws in more complex treatments. This method uses only information extracted from EPID images and it is therefore independent from the linear accelerator.
Publisher: Elsevier BV
Date: 06-2012
Publisher: Bentham Science Publishers Ltd.
Date: 04-2009
Publisher: Wiley
Date: 11-2012
Publisher: Springer Science and Business Media LLC
Date: 06-04-2023
DOI: 10.1007/S13246-023-01246-3
Abstract: Validation of small field dosimetry is crucial for stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). Accurate and considered measurement of linear accelerator dose must be compared to precise and accurate calculation by the treatment planning system (TPS). Monte Carlo calculated distributions contain statistical noise, reducing the reliance that should be given to single voxel doses. The average dose to a small volume of interest (VOI) can minimise the influence of noise, but for small fields introduces significant volume averaging. Similar challenges present during measurement of composite dose from clinical plans when a small volume ionisation chamber is used. This study derived correction factors for VOI averaged TPS doses calculated for small fields, allowing correction to an isocentre dose following account for statistical noise. These factors were used to determine an optimal VOI to represent small volume ionisation chambers during patient specific quality assurance (PSQA). A retrospective comparison of 82 SRS and 28 SBRT PSQA measurements to TPS calculated doses from varying VOI was completed to evaluate the determined volumes. Small field commissioning correction factors of under 5% were obtained for field sizes of 8 mm and larger. Optimal spherical VOI with radius between 1.5 and 1.8 mm and 2.5 to 2.9 mm were determined for IBA CC01 and CC04 ionisation chambers respectively. Review of PSQA confirmed an optimal agreement between CC01 measured doses and a volume of 1.5 to 1.8 mm while CC04 measured doses showed no variation with VOI.
Publisher: Springer Science and Business Media LLC
Date: 17-08-2022
DOI: 10.1007/S00259-022-05927-1
Abstract: This study aimed to develop and assess an automated segmentation framework based on deep learning for metastatic prostate cancer (mPCa) lesions in whole-body [ 68 Ga]Ga-PSMA-11 PET/CT images for the purpose of extracting patient-level prognostic biomarkers. Three hundred thirty-seven [ 68 Ga]Ga-PSMA-11 PET/CT images were retrieved from a cohort of biochemically recurrent PCa patients. A fully 3D convolutional neural network (CNN) is proposed which is based on the self-configuring nnU-Net framework, and was trained on a subset of these scans, with an independent test set reserved for model evaluation. Voxel-level segmentation results were assessed using the dice similarity coefficient (DSC), positive predictive value (PPV), and sensitivity. Sensitivity and PPV were calculated to assess lesion level detection patient-level classification results were assessed by the accuracy, PPV, and sensitivity. Whole-body biomarkers total lesional volume (TLV auto ) and total lesional uptake (TLU auto ) were calculated from the automated segmentations, and Kaplan–Meier analysis was used to assess biomarker relationship with patient overall survival. At the patient level, the accuracy, sensitivity, and PPV were all 90%, with the best metric being the PPV (97.2%). PPV and sensitivity at the lesion level were 88.2% and 73.0%, respectively. DSC and PPV measured at the voxel level performed within measured inter-observer variability (DSC, median = 50.7% vs. second observer = 32%, p = 0.012 PPV, median = 64.9% vs. second observer = 25.7%, p 0.005). Kaplan–Meier analysis of TLV auto and TLU auto showed they were significantly associated with patient overall survival (both p 0.005). The fully automated assessment of whole-body [ 68 Ga]Ga-PSMA-11 PET/CT images using deep learning shows significant promise, yielding accurate scan classification, voxel-level segmentations within inter-observer variability, and potentially clinically useful prognostic biomarkers associated with patient overall survival. This study was registered with the Australian New Zealand Clinical Trials Registry (ACTRN12615000608561) on 11 June 2015.
Publisher: IOP Publishing
Date: 30-05-2012
Publisher: Wiley
Date: 11-01-2012
DOI: 10.1118/1.3673958
Publisher: Walter de Gruyter GmbH
Date: 03-2009
DOI: 10.2478/V10007-009-0008-9
Abstract: [ 61 Cu]diacetyl- bis (N 4 -methylthiosemicarbazone) ([ 61 Cu] ATSM) was prepared using in house-made diacetyl- bis (N 4 -methylthiosemicarbazone) (ATSM) ligand and [ 61 Cu]CuCl 2 produced via the nat Zn(p, x) 61 Cu (180 μA proton irradiation, 22 MeV, 3.2 h) and purified by a ion chromatography method. [ 61 Cu]ATSM radiochemical purity was %, as shown by HPLC and RTLC methods. [ 61 Cu]ATSM was administered into normal and tumor bearing rodents for up to 210 minutes, followed by biodistribution and co-incidence imaging studies. Significant tumor/non-tumor accumulation was observed either by animal sacrification or imaging. [ 61 Cu]ATSM is a positron emission tomography (PET) radiotracer for tumor hypoxia imaging.
Publisher: Springer Science and Business Media LLC
Date: 19-08-2021
DOI: 10.1007/S13246-021-01044-9
Abstract: Planning organ-at-risk volume (PRV) margins can be applied to the bladder and rectum in prostate external beam radiation therapy (EBRT), in order to incorporate the uncertainties resulting from their inter-fraction motion. For each of a total of 16 patients, the bladder and rectum were delineated on CBCT images for five treatment fractions in addition to the planning CT image set. The bladder and rectum boundary displacements across the images were measured and the frequency and size of organ boundary displacements were evaluated. Subsequently, PRV margins were created to cover a specific percentage of organ boundary motion for a specified percentage of the population. In this investigation, two bladder PRV margins were generated to deal with two bladder conditions of low and high-volume variation among fractions. A combined PRV margin was also generated for the rectum by separating the rectum into three parts and deriving independent PRV margins for each segment. Outward coverage and effectiveness metrics allowed evaluation of the margins.
Publisher: Wiley
Date: 18-07-2022
DOI: 10.1002/MP.15840
Abstract: The use of deep learning (DL) to improve cone‐beam CT (CBCT) image quality has gained popularity as computational resources and algorithmic sophistication have advanced in tandem. CBCT imaging has the potential to facilitate online adaptive radiation therapy (ART) by utilizing up‐to‐date patient anatomy to modify treatment parameters before irradiation. Poor CBCT image quality has been an impediment to realizing ART due to the increased scatter conditions inherent to cone‐beam acquisitions. Given the recent interest in DL applications in radiation oncology, and specifically DL for CBCT correction, we provide a systematic theoretical and literature review for future stakeholders. The review encompasses DL approaches for synthetic CT generation, as well as projection domain methods employed in the CBCT correction literature. We review trends pertaining to publications from January 2018 to April 2022 and condense their major findings—with emphasis on study design and DL techniques. Clinically relevant endpoints relating to image quality and dosimetric accuracy are summarized, highlighting gaps in the literature. Finally, we make recommendations for both clinicians and DL practitioners based on literature trends and the current DL state‐of‐the‐art methods utilized in radiation oncology.
Publisher: Informa UK Limited
Date: 11-2015
DOI: 10.2147/MDER.S89725
Publisher: IOP Publishing
Date: 17-07-2012
Publisher: Wiley
Date: 15-02-2023
DOI: 10.1002/MP.16264
Abstract: In prostate radiation therapy, recent studies have indicated a benefit in increasing the dose to intraprostatic lesions (IPL) compared with standard whole gland radiation therapy. Such approaches typically aim to deliver a target dose to the IPL(s) with no deliberate effort to modulate the dose within the IPL. Prostate cancers demonstrate intra‐tumor heterogeneity and hence it is hypothesized that further gains in the optimal delivery of radiation therapy can be achieved through modulation of the dose distribution within the tumor. To account for tumor heterogeneity, biologically targeted radiation therapy (BiRT) aims to utilize a voxel‐wise approach to IPL dose prescription by incorporating knowledge of the spatial distribution of tumor characteristics. The aim of this study was to develop a workflow for generating voxel‐wise optimal dose prescriptions that maximize patient tumor control probability (TCP), and evaluate the feasibility and benefits of applying this workflow on a cohort of 62 prostate cancer patients. The source data for this proof‐of‐concept study included high resolution histology images annotated with tumor location and grade. Image processing techniques were used to compute voxel‐level cell density distribution maps. An absolute tumor cell distribution was calculated via linearly scaling according to published estimated tumor cell numbers. For the IPLs of each patient, optimal dose prescriptions were obtained via three alternative methods for redistribution of IPL boost doses according to maximization of TCP. The radiosensitivity uncertainties were considered using a truncated log‐normally distributed linear radiosensitivity parameter () and compared with Gleason pattern (GP) dependent radiosensitivity parameters that were derived based on previously published methods. An ensemble machine learning method was implemented to identify patient‐specific features that predict the TCP improvement resulting from dose redistribution relative to a uniform dose distribution. The Gleason pattern‐dependent radiosensitivity parameters were calculated for 20 published prostate cancer ratios. Optimal voxel‐level dose prescriptions were generated for all 62 PCa patients. For all dose redistribution scenarios, the optimal dose distribution always shows a higher (or equivalent) TCP level than the uniform dose distribution. The applied random forest regressor could predict patient‐specific TCP improvement with low root mean square error (≤1.5%) by using total tumor number, volume of IPLs and the standard deviation of tumor cell number among all voxels. Biologically‐optimized redistribution of a boost dose can yield TCP improvement relative to a uniform‐boost dose distribution. Patient‐specific tumor characteristics can be used to predict the likelihood of benefit from a redistribution approach for the in idual patient.
Publisher: Elsevier BV
Date: 12-2013
DOI: 10.1016/J.RADONC.2013.08.048
Abstract: To investigate the variability of the global gamma index (γ) analysis in various commercial IMRT/VMAT QA systems and to assess the impact of measurement with low resolution detector arrays on γ. Five commercial QA systems (PTW 2D-Array, Scandidos Delta4, SunNuclear ArcCHECK, Varian EPID, and Gafchromic EBT2 film) were investigated. The response of γ analysis to deliberately introduced errors in pelvis and head & neck IMRT and RapidArc™ plans was evaluated in each system. A theoretical γ was calculated in each commercial QA system software (PTW Verisoft, Delta4 software, SNC Patient, Varian Portal Dosimetry and IBA OmniPro, respectively), using treatment planning system resolution virtual measurements and compared to an independent calculation. Error-induced plans were measured on a linear accelerator and were evaluated against the error-free dose distribution calculated using Varian Eclipse™ in the relevant phantom CT scan. In all cases, global γ was used with a 20% threshold relative to a point selected in a high dose and low gradient region. The γ based on measurement was compared against the theoretical to evaluate the response of each system. There was statistically good agreement between the predicted γ based on the virtual measurements from each software (concordance correlation coefficient, ρc>0.92) relative to the independent prediction in all cases. For the actual measured data, the agreement with the predicted γ reduces with tightening passing criteria and the variability between the different systems increases. This indicates that the detector array configuration and resolution have greater impact on the experimental calculation of γ due to under-s ling of the dose distribution, blurring effects, noise, or a combination. It is important to understand the response and limitations of the gamma index analysis combined with the equipment in use. For the same pass-rate criteria, different devices and software combinations exhibit varying levels of agreement with the predicted γ analysis.
Publisher: Wiley
Date: 22-11-2019
DOI: 10.1002/ACM2.12496
Publisher: Springer Science and Business Media LLC
Date: 27-09-2018
DOI: 10.1007/S13246-018-0690-3
Abstract: Multileaf-collimator (MLC) defined small fields in radiotherapy are used in high dose, ultra-conformal techniques such as stereotactic radiotherapy and stereotactic radiosurgery. Proximity to critical structures and irreversible damage arising from inaccurate delivery mean that correct positioning of the MLC system is of the utmost importance. Some of the existing techniques for MLC positioning quality assurance make use of electronic portal imaging device (EPID) images. However, conventional collimation verification algorithms based on the full width at half maximum (FWHM) fail when applied to small field images acquired by an EPID due to overlapping aperture penumbrae, lateral electron disequilibrium and radiation source occlusion. The objective of this study was to investigate sub-pixel edge detection and other techniques with the aim of developing an automatic and autonomous EPID-based method suitable for MLC positional verification of small static fields with arbitrary shapes. Methods investigated included derivative interpolation, Laplacian of Gaussian (LoG) and an algorithm based on the partial area effect hypothesis. None of these methods were found to be suitable for MLC positioning verification in small field conditions. A method is proposed which uses a manufacturer-specific empirically modified FWHM algorithm which shows improvement over the conventional techniques in the small field size range. With a measured mean absolute difference from planned position for Varian linacs of 0.01 ± 0.26 mm, compared with the erroneous FWHM value of 0.70 ± 0.51 mm. For Elekta linacs the proposed algorithm returned 0.26 ± 0.25 mm, in contrast to the FWHM result of 1.79 ± 1.07 mm.
Publisher: Wiley
Date: 09-2011
Publisher: MDPI AG
Date: 2009
Publisher: Wiley
Date: 11-2012
Publisher: MDPI AG
Date: 04-2020
Abstract: Advances in imaging have enabled the identification of prostate cancer foci with an initial application to focal dose escalation, with subvolumes created with image intensity thresholds. Through quantitative imaging techniques, correlations between image parameters and tumour characteristics have been identified. Mathematical functions are typically used to relate image parameters to prescription dose to improve the clinical relevance of the resulting dose distribution. However, these relationships have remained speculative or invalidated. In contrast, the use of radiobiological models during treatment planning optimisation, termed biological optimisation, has the advantage of directly considering the biological effect of the resulting dose distribution. This has led to an increased interest in the accurate derivation of radiobiological parameters from quantitative imaging to inform the models. This article reviews the progress in treatment planning using image-informed tumour biology, from focal dose escalation to the current trend of in idualised biological treatment planning using image-derived radiobiological parameters, with the focus on prostate intensity-modulated radiotherapy (IMRT).
Location: Iran (Islamic Republic of)
Location: Australia
No related grants have been discovered for Pejman Rowshanfarzad.