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3. Skin dose investigations on a 0.5 T parallel rotating biplanar linac‐MR using Monte Carlo simulations and measurements.

Author

Oliver, Patricia A. K., Yip, Eugene, Tari, Shima Y., Wachowicz, Keith, Reynolds, Michael, Burke, Ben, Warkentin, Brad, and Fallone, B. Gino

Subjects
MAGNETIC field effects, IONIZATION chambers, MAGNETIC fields, ION plating, MAGNETIC particles, PHOTON beams
Abstract

Background: The Alberta rotating biplanar linac‐MR has a 0.5 T magnetic field parallel to the beamline. When developing a new linac‐MR system, interactions of charged particles with the magnetic field necessitate careful consideration of skin dose and tissue interface effects. Purpose: To investigate the effect of the magnetic field on skin dose using measurements and Monte Carlo (MC) simulations. Methods: We develop an MC model of our linac‐MR, which we validate by comparison with ion chamber measurements in a water tank. Additionally, MC simulation results are compared with radiochromic film surface dose measurements on solid water. Variations in surface dose as a function of field size are measured using a parallel plate ion chamber in solid water. Using an anthropomorphic computational phantom with a 2 mm‐thick skin layer, we investigate dose distributions resulting from three beam arrangements. Magnetic field on and off scenarios are considered for all measurements and simulations. Results: For a 20 × 20 cm2 field size, D0.2cc${D_{0.2cc}}$ (the minimum dose to the hottest contiguous 0.2 cc volume) for the top 2 mm of a simple water phantom is 72% when the magnetic field is on, compared to 34% with magnetic field off (values are normalized to the central axis dose maximum). Parallel plate ion chamber measurements demonstrate that the relative increase in surface dose due to the magnetic field decreases with increasing field size. For the anthropomorphic phantom, D∼0.2cc${D_{ \sim 0.2cc}}$ (minimum skin dose in the hottest 1 × 1 × 1 cm3 cube) shows relative increases of 20%–28% when the magnetic field is on compared to when it is off. With magnetic field off, skin D∼0.2cc${D_{ \sim 0.2cc}}$ is 71%, 56%, and 21% for medial‐lateral tangents, anterior‐posterior beams, and a five‐field arrangement, respectively. For magnetic field on, the corresponding skin D∼0.2cc${D_{ \sim 0.2cc}}$ values are 91%, 67%, and 25%. Conclusions: Using a validated MC model of our linac‐MR, surface doses are calculated in various scenarios. MC‐calculated skin dose varies depending on field sizes, obliquity, and the number of beams. In general, the parallel linac‐MR arrangement results in skin dose enhancement due to charged particles spiraling along magnetic field lines, which impedes lateral motion away from the central axis. Nonetheless, considering the results presented herein, treatment plans can be designed to minimize skin dose by, for example, avoiding oblique beams and using a larger number of fields. [ABSTRACT FROM AUTHOR]

Published
2024
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6. Seminal Vesicle Treatment for Localized Prostate Cancer Treated with External Beam Radiotherapy.

Author

Steed, Tanner, Chopra, Nikki, Yun, Jihyun, Hill, Jordan, Burke, Benjamin, Ghosh, Sunita, Warkentin, Brad, and Usmani, Nawaid

Subjects
EXTERNAL beam radiotherapy, SEMINAL vesicles, PROSTATE cancer, PROSTATE cancer patients
Abstract

This study retrospectively reviewed data from men with localized prostate cancer treated with external beam radiotherapy (EBRT). We identified 359 men with localized prostate cancer treated with curative EBRT at the Cross Cancer Institute between 2010–2011. The volume of seminal vesicles (SVs) treated as well as dose values were extracted. These volumes were compared to gold standard contours drawn by a trained expert based on consensus European Society for Radiotherapy and Oncology (ESTRO) contouring guidelines. Patient and tumor characteristics were extracted for these patients. Memorial Sloan Kettering prostate cancer nomogram was used to assign a predicted risk of SV involvement for each patient based on baseline tumor characteristics. In patients with a predicted risk of SV involvement greater than 15% (n = 184), 86.5% (SD = 18.6) of the base of the SVs were treated with EBRT, compared to 66.7% (SD = 32.6) for patients with a predicted risk of SV involvement less than 15% (n = 175, p < 0.0001). Similarly, the mean percentage of proximal and total SV volumes treated with EBRT was 75.6% (SD = 24.4) and 68.7% (SD = 26.0) for patients with a predicted risk of SV involvement of greater than 15%, compared to 50.3% (SD = 31.0, p < 0.0001) and 41.0% (SD = 27.8, p < 0.0001) for patients with a risk of less than 15%. The results indicate that all parts of the SVs are more likely to be contoured in men with >15% risk of SV involvement than those with <15% risk. However, radiation oncologists still contour a high percentage of SVs in men with <15% risk of SV involvement, suggesting that there may be over-treatment of SVs that increases the risk of rectal or bladder toxicity. [ABSTRACT FROM AUTHOR]

Published
2023
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7. Tumor Volume Predicts for Pathologic Complete Response in Rectal Cancer Patients Treated With Neoadjuvant Chemoradiation

Author

Yang, Fan, primary, Hill, Jordan, additional, Abraham, Aswin, additional, Ghosh, Sunita, additional, Steed, Tanner, additional, Kurtz, Clay, additional, Joseph, Kurian, additional, Yun, Jihyun, additional, Warkentin, Brad, additional, Thai, JoAnn, additional, Nijjar, Tirath, additional, Severin, Diane, additional, Tankel, Keith, additional, Fairchild, Alysa, additional, and Usmani, Nawaid, additional

Published
2022
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12. More Is Not Better When It Comes to Treating Rectal Cancer With Multimodal Chemoradiation Beyond the Standard Radiation Dose of 5040 cGy

Author

Abraham, Aswin George, primary, Joseph, Kurian, additional, Ghosh, Sunita, additional, Yun, Jihyun, additional, Warkentin, Brad J., additional, Thai, JoAnn J., additional, Cheung, Winson Y., additional, Xu, Yuan, additional, Nijjar, Tirath S., additional, Severin, Diane M., additional, Tankel, Keith, additional, Fairchild, Alysa M., additional, and Usmani, Nawaid, additional

Published
2022
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14. 29: Tumour Volume Predicts for Pathological Complete Response in Rectal Cancer Patients Treated with Neoadjuvant Chemoradiation

Author

Yang, Fan, primary, Hill, Jordan, additional, Abraham, Aswin, additional, Ghosh, Sunita, additional, Steed, Tanner, additional, Kurtz, Clay, additional, Joseph, Kurian, additional, Yun, Jihyun, additional, Warkentin, Brad, additional, Thai, JoAnn, additional, Nijjar, Tirath, additional, Severin, Diane, additional, Tankel, Keith, additional, Fairchild, Alysa, additional, and Usmani, Nawaid, additional

Published
2021
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15. Disassembly of microtubules by intense terahertz pulses

Author

Hough, Cameron M., primary, Purschke, David N., additional, Bell, Clayton, additional, Kalra, Aarat P., additional, Oliva, Patricia J., additional, Huang, Chenxi, additional, Tuszynski, Jack A., additional, Warkentin, Brad J., additional, and Hegmann, Frank A., additional

Published
2021
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19. Developing a tri-hybrid algorithm to predict patient x-ray scatter into planar imaging detectors for therapeutic photon beams

Author

Elbakri, Idris (Physics and Astronomy) VanUytven, Eric (Physics and Astronomy) Lin, Francis (Physics and Astronomy) Wang, Yang (Computer science) Warkentin, Brad (Department of Oncology, University of Alberta), McCurdy, Boyd (Physics and Astronomy), Guo, Kaiming, Elbakri, Idris (Physics and Astronomy) VanUytven, Eric (Physics and Astronomy) Lin, Francis (Physics and Astronomy) Wang, Yang (Computer science) Warkentin, Brad (Department of Oncology, University of Alberta), McCurdy, Boyd (Physics and Astronomy), and Guo, Kaiming

Abstract

In vivo dosimetry via transmission imaging of the therapy beam can verify the intended treatment plan was delivered to the patient. However, the EPID (electronic portal imaging device) transmission images are contaminated with patient-generated scattered photons. If this component can be accurately estimated, its effect can be removed and therefore the resulting in vivo patient dose estimate will be more accurate. This thesis presents the development of a ‘tri-hybrid’ (TH) algorithm to provide accurate estimates of patient-generated photon scatter at the EPID. The TH method combines three approaches: 1) Analytical methods to solve exactly for singly-scattered photon fluence. 2) For multiply scattered photon fluence, a modified hybrid Monte Carlo (MC) simulation method was applied, using only a few thousand histories. From each second and higher-order interaction site in the MC simulation, energy fluence entering all pixels of the EPID scoring plane was calculated using analytical methods. 3) For the bremsstrahlung and positron annihilation component, a convolution/superposition approach was employed using pre-generated pencil beam scatter kernels superposed on the incident fluence. Since no experimental measurement method is available to directly confirm the separate subcomponents of photon scatter, a Monte Carlo simulation tool was developed to separately score them. This tool was used as the ‘gold standard’ for the development and validation of the TH method. The TH-predicted total patient-scattered photon fluence entering the EPID, as well its energy spectra, are compared with full Monte Carlo simulation (EGSnrc) for validation. A variety of phantoms are tested, including simple slab and anthropomorphic CT, as well as monoenergetic and polyenergetic beams with different field sizes. For these tests, the proposed TH method was demonstrated to be in good agreement with full Monte Carlo simulation, generally within 1%. Parameters of the TH method were optimized to m

Published
2020

20. 184 Analysis of Radiation Dosimetry Predictive for Toxicity in Rectal Cancer Patients Treated with Long Course Chemo-Radiation

Author

Abraham, Aswin George, primary, Thai, JoAnn, additional, Ghosh, Sunita, additional, Warkentin, Brad, additional, Yun, Jihyun, additional, Severin, Diane, additional, Tankel, Keith, additional, Joseph, Kurian, additional, Nijjar, Tirath, additional, Fairchild, Alysa, additional, Cheung, Winson, additional, and Xu, Yuan, additional

Published
2019
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27. Spatial and temporal distribution of gamma H2AX fluorescence in human cell cultures following synchrotron-generated X-ray microbeams : lack of correlation between persistent gamma H2AX foci and apoptosis

Author

Anderson, Danielle L., Mirzayans, Razmik, Andrais, Bonnie, Siegbahn, E. Albert, Fallone, B. Gino, Warkentin, Brad, Anderson, Danielle L., Mirzayans, Razmik, Andrais, Bonnie, Siegbahn, E. Albert, Fallone, B. Gino, and Warkentin, Brad

Abstract

Formation of gamma H2AX foci (a marker of DNA double-strand breaks), rates of foci clearance and apoptosis were investigated in cultured normal human fibroblasts and p53 wild-type malignant glioma cells after exposure to high-dose synchrotron-generated microbeams. Doses up to 283 Gy were delivered using beam geometries that included a microbeam array (50 mu m wide, 400 mu m spacing), single microbeams (60-570 mu m wide) and a broad beam (32 mm wide). The two cell types exhibited similar trends with respect to the initial formation and time-dependent clearance of gamma H2AX foci after irradiation. High levels of gamma H2AX foci persisted as late as 72 h post-irradiation in the majority of cells within cultures of both cell types. Levels of persistent foci after irradiation via the 570 mu m microbeam or broad beam were higher when compared with those observed after exposure to the 60 mu m microbeam or microbeam array. Despite persistence of gamma H2AX foci, these irradiation conditions triggered apoptosis in only a small proportion (<5%) of cells within cultures of both cell types. These results contribute to the understanding of the fundamental biological consequences of high-dose microbeam irradiations, and implicate the importance of non-apoptotic responses such as p53-mediated growth arrest (premature senescence)., AuthorCount:6

Published
2014
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37. 48 The Impact of Seminal Vesicle Treatment on the Risk of Biochemical Recurrence in Patients with Localized Prostate Cancer Treated with External Beam Radiotherapy.

Author

Steed, Tanner, Hill, Jordan, Chopra, Nikki, Taher, Sumayya, Islam, Raiyana, Gorman, Mathew, Ghosh, Sunita, Yun, Jihyun, Burke, Benjamin, Warkentin, Brad, Steed, Jackson, and Usmani, Nawaid

Subjects
*EXTERNAL beam radiotherapy, *SEMINAL vesicles, *PROSTATE cancer patients, *DISEASE relapse
Published
2024
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38. Poster - 15: Air kerma rate measurements using a cylindrical free-air ionization chamber on the 05B1-1 beamline at the Canadian Light Source

Author

Warkentin, Brad [BCCA - Sindi Ahluwalia Hawkins Centre for the Southern Interior, Kelowna BC, Stockholm University, Sweden, Cross Cancer Institute, Alberta Health Services and University of Alberta, Edmonton AB, Cross Cancer Institute, Alberta Health Services and University of Alberta, Edmonton AB (Sweden)]

Published
2016
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