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Session: Advanced Dosimetry and Monte Carlo Simulation [Return to Session]

Monte Carlo Simulation of Uniformly and Non-Uniform Loaded Generic and Notched Eye Plaques

O Semeniuk*, V Malkov, R Weersink, Princess Margaret Cancer Centre, Toronto, ON,CA


WE-C930-IePD-F3-1 (Wednesday, 7/13/2022) 9:30 AM - 10:00 AM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 3

Purpose: To investigate the effect of non-uniform loading on dose distribution for generic and notched eye plaques.

Methods: Using EGSnrc Monte Carlo (MC) simulations, we investigate eye plaque dose distributions in water and in an anatomically representative eye phantom. Simulations were performed in accordance with TG-43 formalism and compared against full MC simulations which account for inter-seed and inhomogeneity effects.

Results: Uniformly and non-uniformly loaded plaque dose distributions in water showed virtually no difference between each other. Furthermore, upon normalization, there is almost no difference in the center of the plaque profiles between TG43 and full MC simulations after the first few millimeters from the eye/silastic interface, within which TG43 formalism tends to overestimate the dose. However, despite normalization, there is a pronounced lateral change in dose distributions. The full width at half maximum generic eye plaques is ~10% lower in full MC vs TG43 due to the inclusion of inhomogeneities and inter-seed effects. Eye phantom simulations showed that the lateral dose contraction impacts favorably the eye dose distribution. Thus, for 16 mm both uniformly and non-uniformly loaded plaques, TG43 overestimates the dose to the organs at risk, while underestimates the target coverage.

Conclusion: With individual normalization of MC and TG43, TG43 calculations overestimate the lateral dose distribution of both generic and notched eye plaques, leading to the dose overestimation for the organs at risk (optic nerve, iris, lens, etc.) and underestimation of target coverage. The dose matching along the central axis for the non-uniformly loaded plaques to that of uniformly loaded ones was found to be sufficient for providing a comparable coverage and can be clinically used in eye-cancer-busy centers. The developed eye and notched plaques models might be used to facilitate the development of the MC-based treatments for patient-specific eye lesions with both uniformly and non-uniformly loaded plaques.


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