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Generation of 3D Dosimetric Reference Datasets Using Model-Based Dose Calculations for COMS Eye Plaque Brachytherapy

E Fletcher1*, F Ballester2, L Beaulieu3, Y Ma3, H Morrison4, MJ Rivard5, R Sloboda6, J Vijande2, R Thomson1, (1) Carleton University, Ottawa, ON, CA, (2) University of Valencia (UV-IFIC-IRIMED), Burjassot, ES, (3) CHU de Quebec - Universite Laval, Quebec, QC, CA, (4) Tom Baker Cancer Centre, Calgary, AB, CA, (5) Rhode Island Hospital / Brown University, Providence, RI, USA, (6) Cross Cancer Institute, Edmonton, AB, CA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To compare results from several Monte Carlo (MC) based dose calculation algorithms used to evaluate the dosimetry of brachytherapy treatments for intraocular tumours in order to develop test cases for adopters of model-based dose calculation algorithms (MBDCAs). The scenario being investigated involves the treatment of ocular melanoma using a Collaborative Ocular Melanoma Study (COMS) 16 mm eye plaque loaded with model 6711 125I seeds.

Methods: The levels of agreement among four MC codes (egs_brachy (EGSnrc), ALGEBRA (GEANT4), Penelope2014, and MCNP6) were evaluated by comparing the results from various test cases. These included air kerma and dose to water for a single seed, 13 seeds individually or in combination in water and positioned as in the 16 mm plaque, and finally the full COMS plaque loaded with 13 seeds with dose to water. Dose comparisons were made using (0.5 mm)3 voxels across the whole scoring phantom as well as along various slices of the phantom.

Results: All air kerma results were within 0.2%, with the exception of Penelope which differed by 3%. These variations are due to the physical models used for low-energy (below 100 keV) cross sections. For a single seed in water, ALGEBRA and MCNP were within 1% and Penelope was within 2% of egs_brachy. For simulations including all 13 seeds, comparing local percentage dose differences across the scoring volume, ALGEBRA was 0.6% higher, MCNP was 1.1% lower, and Penelope was 1.0% higher than egs_brachy. Variations in the percentage dose differences were much larger when the plaque was fully modelled than when simulating a water environment.

Conclusion: This work indicates that the MC codes studied exhibited excellent agreement (within 2%) for these test cases. Next steps for this research include simulations with sample patient CT data, as well as comparisons with the OncentraBrachy/ACE commercial treatment planning system.

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Funding Support, Disclosures, and Conflict of Interest: Funding: Natural Sciences and Engineering Research Council (NSERC) of Canada Canada Research Chairs Ontario Ministry of Research and Innovation COI: none

Keywords

Not Applicable / None Entered.

Taxonomy

TH- Brachytherapy: Computational dosimetry: Monte Carlo

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