ORCID Profile
0000-0001-8482-6982
Current Organisations
University of Adelaide
,
Royal Adelaide Hospital
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Publisher: Wiley
Date: 25-12-2019
DOI: 10.1002/MP.13935
Abstract: Protons and heavy ions are considered to be ideal particles for use in external beam radiotherapy due to the superior properties of the dose distribution. While a photon (x-ray) beam delivers considerable dose to healthy tissues around the tumor, a proton beam that is delivered with sufficient energies has: a low entrance dose (the dose in front of the tumor) a high-dose region within the tumor, known as the Bragg peak and, no exit dose beyond the tumor. Proton therapy is the next major step in advancing radiotherapy treatment. The purpose of this project was to adapt an existing radioisotope production cyclotron, a General Electric (GE) PETtrace, to enable radiobiological studies using proton beams. During routine use the PETtrace delivers 16.5 MeV protons to target with beam currents in the range of 10-100 µA resulting in dose rates in the order of kGy/s. To achieve the aim of the project the dose rate had to be reduced to the Gy/min range, without attenuating the proton energy below 5 MeV. This paper covers the design, construction and validation of the beam port. Monte Carlo simulations were performed, using GEANT4, SRIM and PACE4 to design the beam port and optimize its components. Once the beam port was fabricated, validation experiments were performed using EBT3 and HD-V2 Gafchromic™ films, and a Keithley 6485 pico ere meter. The external beam port was successfully modeled, designed and fabricated. By using a 0.25 mm thick gold foil and a brass pin-hole collimator the beam was spread from a narrow full beam diameter of 10 mm to a wide beam with a 5% flatness area in the center of the beam that had a diameter of ~20 mm. In using this system the dose rate was reduced from kGy/s to ~30 Gy/min.
Publisher: Springer Science and Business Media LLC
Date: 08-08-2019
DOI: 10.1007/S13246-019-00785-Y
Abstract: Respiratory gated treatments are now common in order to reduce tumour motion uncertainties due to breathing. One issue associated with gated treatments is the time delay between the gating system and the linear accelerator. In this study we develop and characterise an affordable phantom to be used in routine and patient specific quality assurance (QA) of the Varian Real-Time Position Management™ (RPM) system. A photodiode has been incorporated into the phantom in order to estimate the time delay. A commercial Quasar phantom was customised to incorporate two stepper motors which independently control an anterior-posterior abdomen/thorax moving plate, and an inferior-superior moving lung insert. A photodiode placed in the path of the radiation is used to measure when beam on/off occurs. Two Arduino microcontroller boards have been utilised to control the motors, read the photodiode and write to an SD card. The measured beam on/off, correlated to the known positions of the phantom is compared to the gate window for RPM. The time delay was measured for sinusoidal movements with a period of 7.50 s and 3.75 s, and for three patient breathing traces. For the sinusoidal movements, time delays of 150 ± 34 ms and 39 ± 34 ms were measured, for 7.50 s and 3.75 s periods, respectively. In the case of the patients' breathing traces time delays of 135 ± 26 ms, 137 ± 34 ms and 129 ± 28 ms were measured. An affordable motion phantom has been developed for routine and patient specific QA of respiratory gating systems. It is capable of reproducing a patient's breathing waveform and performing time delay measurements with a photodiode. Results indicate a time delay of the order of 0.1-0.2 s for the RPM system.
Publisher: Elsevier BV
Date: 12-2020
Publisher: American Chemical Society (ACS)
Date: 13-07-2021
Publisher: IOP Publishing
Date: 10-2020
DOI: 10.1088/1742-6596/1662/1/012009
Abstract: In radiotherapy practice, 1D and 2D dosimeters are used for dose verification prior to patient treatment. Along with high accuracy and precision of dose measurements that these dosimeters provide, acquisition of dose deposition data in three dimensions requires extrapolation of measured data. Development of a 3D dosimeter would provide continuous information of dose distribution in matter. In this work, NaCl 3D crystal has shown that radiation deposition can be imaged using blue laser stimulation in two dimensions. It was further shown that the intensity of collected signal has near – linear dose dependence, however complete signal readout is required, to compensate for gradual signal collection at different depths along the profile of the stimulating laser beam, due to attenuation of the beam within the crystal. A method to extend dose measurement to three dimensions using imaging is proposed.
Publisher: Informa UK Limited
Date: 21-12-2020
Publisher: IOP Publishing
Date: 10-2020
DOI: 10.1088/1742-6596/1662/1/012029
Abstract: Recent reports have shown both poly (methyl methacrylate) (PMMA) and silica optical fibres to be ionization quenching free, making them possibly very useful dosimeters for proton beams. In this study, the response from PMMA and silica optical fibres to therapeutic proton beams are evaluated. The light output was recorded from both optical fibres, exposed to varying dose-rates of 0.5 Gy/min to 20 Gy/min from a 235 MeV isochronous cyclotron. The PMMA optical fibre was observed to have a linear dose-rate response, and a constant light emission for a constant dose-rate exposure. However, in the case of the silica optical fibres, the light output was observed to increase during a constant dose-rate exposure. If uncorrected, this accumulated dose sensitivity observed in the silica optical fibres can result in erroneous measurements.
Publisher: Springer Science and Business Media LLC
Date: 27-10-2016
Publisher: Elsevier BV
Date: 02-2021
Publisher: Wiley
Date: 16-03-2021
DOI: 10.1002/MP.14780
Publisher: Elsevier BV
Date: 12-2021
Publisher: Elsevier BV
Date: 11-2014
Publisher: Elsevier BV
Date: 03-2019
Publisher: The Optical Society
Date: 20-02-2014
DOI: 10.1364/OE.22.004559
Publisher: Elsevier BV
Date: 02-2021
Publisher: Elsevier BV
Date: 09-2019
DOI: 10.1016/J.BRACHY.2019.05.006
Abstract: We propose a novel method of designing surface mold brachytherapy applicators using optical photogrammetry. The accuracy of this technique for the purpose of 3D-printing surface mold brachytherapy applicators is investigated. Photogrammetry was used to generate a 3D model of a patient's right arm. The geometric accuracy of the model was evaluated against CT in terms of volume, surface area, and the Hausdorff distance. A surface mold applicator was then 3D printed using this reconstructed model. The accuracy was evaluated by analyzing the displacement and air-gap volumes between the applicator and plaster cast on a CT image. This technique was subsequently applied to generate a 3D-printed applicator of the author's hand directly, as a proof of principle, using only photographic images. The volume and surface area of the model were within 0.1% and 2.6% of the CT-obtained values, respectively. Using the Hausdorff distance metric, it was determined that 93% of the visible vertices present in the CT-derived model had a matching vertex on the photogrammetry-derived model within 1 mm, indicating a high level of similarity. The maximum displacement between the plaster cast of the patient's arm and the photo-derived 3D-printed applicator was 1.2 mm with a total air-gap volume of approximately 0.05 cm Photogrammetry has been applied to the task of generating 3D-printed brachytherapy surface mold applicators. The current work demonstrates the feasibility and accuracy of this technique and how it may be incorporated into a 3D-printing brachytherapy workflow.
Publisher: MDPI AG
Date: 02-05-2022
Abstract: Hypofractionated radiotherapy is an attractive approach for minimizing patient burden and treatment cost. Technological advancements in external beam radiotherapy (EBRT) delivery and image guidance have resulted in improved targeting and conformality of the absorbed dose to the disease and a reduction in dose to healthy tissue. These advances in EBRT have led to an increasing adoption and interest in hypofractionation. Furthermore, for many treatment sites, proton beam therapy (PBT) provides an improved absorbed dose distribution compared to X-ray (photon) EBRT. In the past 10 years there has been a notable increase in reported clinical data involving hypofractionation with PBT, reflecting the interest in this treatment approach. This review will discuss the reported clinical data and radiobiology of hypofractionated PBT. Over 50 published manuscripts reporting clinical results involving hypofractionation and PBT were included in this review, ~90% of which were published since 2010. The most common treatment regions reported were prostate, lung and liver, making over 70% of the reported results. Many of the reported clinical data indicate that hypofractionated PBT can be well tolerated, however future clinical trials are still needed to determine the optimal fractionation regime.
Publisher: Hindawi Limited
Date: 16-08-2013
DOI: 10.1111/ECC.12109
Abstract: Technological advances in both diagnosis and treatment of breast cancer lead to early detection and better treatment management. Consequently, the population of long-term survivors is on the rise. The risk of developing second cancers among breast cancer survivors was shown to be higher than that for the general population. The aim of this work was to review the literature on the risk of second primary cancer (SPC) after breast irradiation. Pubmed search of population-based studies on SPC after breast irradiation was conducted and the findings (in terms of Standardised Incidence Ratio) were collated and discussed. Several studies confirmed the link between breast tumour irradiation and risk of SPC, showing a small, but valid risk. There are, however, confounding factors that can either underestimate or overestimate risks: misclassification of tumour status, genetic inheritance, smoking, environmental factors, and the lack of accurate data in cancer registries. While isolating these potential triggers might be difficult, this approach would allow better discernability between radiotherapy-related risks and those generated by other factors. It is also important to evaluate the current status of treatment-related late effects and to lower such risks by minimising the dose delivered to normal tissues.
Publisher: Elsevier BV
Date: 06-2013
Publisher: Wiley
Date: 09-10-2015
DOI: 10.1118/1.4931968
Abstract: The authors evaluate the capability of a beryllium oxide (BeO) ceramic fiber-coupled luminescence dosimeter, named radioluminescence/optically stimulated luminescence (RL/OSL) BeO FOD, for dosimetric verification of high dose rate (HDR) treatments. The RL/OSL BeO FOD is capable of RL and OSL measurements. The RL/OSL BeO FOD is able to be inserted in 6F proguide needles, used in interstitial HDR treatments. Using a custom built Perspex phantom, 6F proguide needles could be submerged in a water tank at 1 cm separations from each other. A second background fiber was required to correct for the stem effect. The stem effect, dose linearity, reproducibility, depth-dose curves, and angular and temperature dependency of the RL/OSL BeO FOD were characterised using an Ir-192 source. The RL/OSL BeO FOD was also applied to the commissioning of a 10 mm horizontal Leipzig applicator. Both the RL and OSL were found to be reproducible and their percentage depth-dose curves to be in good agreement with those predicted via TG-43. A combined uncertainty of 7.9% and 10.1% (k=1) was estimated for the RL and OSL, respectively. For the 10 mm horizontal Leipzig applicator, measured percentage depth doses were within 5% agreement of the published reference calculations. The output at the 3 mm prescription depth for a 1 Gy delivery was verified to be 0.99±0.08 Gy and 1.01±0.10 Gy by the RL and OSL, respectively. The use of the second background fiber under the current setup means that the two fibers cannot fit into a single 6F needle. Hence, use of the RL is currently not adequate for the purpose of in vivo brachytherapy dosimetry. While not real-time, the OSL is shown to be adequate for in vivo brachytherapy dosimetry.
Publisher: Springer Science and Business Media LLC
Date: 12-04-2021
Publisher: IEEE
Date: 08-2011
Publisher: Springer Science and Business Media LLC
Date: 12-01-2022
DOI: 10.1007/S13246-021-01092-1
Abstract: In this study, we investigate whether an acceptable dosimetric plan can be obtained for a brachytherapy surface applicator designed using photogrammetry and compare the plan quality to a CT-derived applicator. The nose region of a RANDO anthropomorphic phantom was selected as the treatment site due to its high curvature. Photographs were captured using a Nikon D5600 DSLR camera and reconstructed using Agisoft Metashape while CT data was obtained using a Canon Aquillion scanner. Virtual surface applicators were designed in Blender and printed with PLA plastic. Treatment plans with a prescription dose of 3.85 Gy × 10 fractions with 100% dose to PTV on the bridge of the nose at 2 mm depth were generated separately using AcurosBV in the Varian BrachyVision TPS. PTV D
Publisher: Springer Science and Business Media LLC
Date: 27-07-2020
Publisher: Elsevier BV
Date: 02-2015
Publisher: Elsevier BV
Date: 09-2019
DOI: 10.1016/J.EJMP.2019.08.021
Abstract: The purpose of this study was to investigate the potential of real-time optically stimulated luminescence (rtOSL) measurements of a beryllium oxide (BeO) ceramic fibre-coupled luminescence dosimetry system. By pulsing the stimulation laser during the exposure to ionizing radiation, an rtOSL dose-rate measurement can be obtained which could be stem effect free. A portable rtOSL BeO ceramic fibre-coupled dosimetry system is presented and characterized using a constant dose-rate superficial 140 kVp X-ray beam. The rtOSL was measured for dose-rates between 0.29 and 3.88 Gy/min, controlled by varying the source to surface distance. After correcting for OSL decay during the exposure, a linear dose-rate response of the change in rtOSL (ΔrtOSL) was observed. The ΔrtOSL was also observed to be stem effect free.
Publisher: Springer Science and Business Media LLC
Date: 10-08-2020
Publisher: Informa UK Limited
Date: 05-07-2016
Publisher: Springer Science and Business Media LLC
Date: 30-05-2023
DOI: 10.1007/S13246-023-01279-8
Abstract: In high-dose-rate (HDR) prostate brachytherapy the combined effect of uncertainties cause a range of possible dose distributions deviating from the nominal plan, and which are not considered during treatment plan evaluation. This could lead to dosimetric misses for critical structures and overdosing of organs at risk. A robust evaluation method to assess the combination of uncertainties during plan evaluation is presented and demonstrated on one HDR prostate ultrasound treatment plan retrospectively. A range of uncertainty scenarios are simulated by changing six parameters in the nominal plan and calculating the corresponding dose distribution. Two methods are employed to change the parameters, a probabilistic approach using random number s ling to evaluate the likelihood of variation in dose distributions, and a combination of the most extreme possible values to access the worst-case dosimetric outcomes. One thousand probabilistic scenarios were run on the single treatment plan with 43.2% of scenarios passing seven of the eight clinical objectives. The prostate D 90 had a standard deviation of 4.4%, with the worst case decreasing the dose by up to 27.2%. The urethra D 10 was up to 29.3% higher than planned in the worst case. All DVH metrics in the probabilistic scenarios were found to be within acceptable clinical constraints for the plan under statistical tests for significance. The clinical significance of the results from the robust evaluation method presented on any in idual treatment plan needs to be compared in the context of a historical data set that contains patient outcomes with robustness analysis data to ascertain a baseline acceptance.
Publisher: Wiley
Date: 29-05-2014
DOI: 10.1118/1.4889694
Publisher: Elsevier BV
Date: 09-2019
DOI: 10.1016/J.EJMP.2019.08.001
Abstract: An investigation into the response of optical fibres to 16.5 MeV protons is presented here. A silica and a poly(methyl methacrylate) (PMMA) optical fibre was exposed to 16.5 MeV protons from a GE PETtrace cyclotron. The optical fibres were exposed to beam currents of 30nA - 270nA and the emission spectrum analysed. The silica fibre was the most sensitive and had two main peaks at 460 nm and 650 nm. The ratio between the peaks was observed to increase as irradiation of the fibres continued, where the 460 nm peak increased at a rate >4 times the 650 nm peak. The rate of increase of the ratio between the peaks was observed to be constant at a constant target current and linear with target current. In the case of the PMMA fibre, significant spectral changes were observed during the exposure to 16.5 MeV protons. A simple method for estimating the effect of photodarkening and activation is presented here and indicated that the changes in the spectrum for the PMMA fibres may be due to photodarkening and activation.
No related grants have been discovered for Alexandre Santos.