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Applications of Egs_brachy for Patient-Specific Model-Based Dose Calculations for Brachytherapy

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S Deering

S Deering1*, M Hilts2 3 , R Taylor1 , R Thomson1 , (1) Carleton University, Ottawa, ON, Canada, (2) BC Cancer Agency, Kelowna, BC, Canada, (3) University of British Columbia - Okanagan, Kelowna, BC, Canada


WE-AB-605-4 (Wednesday, August 2, 2017) 7:30 AM - 9:30 AM Room: 605

Purpose: egs_brachy is a recently-developed EGSnrc application for rapid Monte Carlo (MC) brachytherapy dose calculations. This work investigates the capabilities of egs_brachy to model photon and beta-emitting sources, applicator/shield geometries, and detailed patient-specific models in several brachytherapy contexts.

Methods: Computational ophthalmic applicator models are constructed for the plaques of the Collaborative Ocular Melanoma Study (COMS) (diameters 10 to 24 mm) containing photon-emitting brachytherapy seeds (¹²⁵I or ¹⁰³Pd) and for BEBIG ¹⁰⁶Ru beta-emitting plaques (diameters 11.6 to 25.4 mm). Computed dose distributions for plaques in water are compared with published values from different MC codes. Considering breast ¹⁰³Pd seed brachytherapy, patient CT images and physician-contoured structures are used to develop detailed patient-specific virtual phantoms including non-water tissue, in addition to models of external lead shields employed for radiation protection. egs_brachy simulations of photon sources (¹²⁵I and ¹⁰³Pd) involve detailed geometric seed models that were previously benchmarked.

Results: Dose distributions for both photon- and beta-emitting plaques show excellent agreement with published values. For COMS plaques, egs_brachy doses agree with published BrachyDose and MCNP5 values within statistical uncertainties (sub-1% in tumor). Similarly, egs_brachy doses for ¹⁰⁶Ru beta-emitting plaques agree within statistical uncertainties (sub-2%) with recently-published PENELOPE values, notable due to the historically poor agreement between published doses from different MC codes. For breast seed brachytherapy, egs_brachy can fully model ¹⁰³Pd seeds and the protective lead shield within detailed voxelized phantoms to compute doses to segmented gland/adipose breast tissues, as well as surrounding structures (such as skin, lungs, heart, and ribs).

Conclusion: egs_brachy can accurately model detailed geometries involving applicators, shielding, photon and beta sources, and sophisticated patient-specific models. Soon to be released as free, open-source software to the research community, egs_brachy shows promise for use in a broad range of brachytherapy applications.

Funding Support, Disclosures, and Conflict of Interest: National Science and Engineering Research Council of Canada, Canada Research Chairs, Ministry of Research and Innovation of Ontario, Ontario Graduate Scholarship

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