Program Information
Monte Carlo Study of 3D Dose Distributions for COMS Eye Plaques
J Gloss*, C Watchman , University of Arizona, Tucson, AZ
Presentations
SA-B-BRD-10 (Saturday, March 5, 2016) 10:30 AM - 12:30 PM Room: Grand Ballroom D
Purpose: The purpose of our study is to investigate heterogeneity correction factors for three different vendor seed models using a Monte Carlo transport code to compute the three dimensional dose distributions for COMS eye plaques as recommended by TG-186.
Methods: Monte Carlo N-Particle transport code (MCNP5) was used for Monte Carlo simulations. Three different vendor models were investigated: Amersham Oncoseed 6711, Best Medical 2301, and IsoAid IAI-125. Seed characteristics were benchmarked against TG-43 and existing literature to verify the seed models. Simulations of COMS plaques ranging from 10 mm to 22 mm were evaluated for three dimensional dose distributions in a heterogeneous medium and a homogeneous water medium. Heterogeneity correction factors were calculated, and off axis factors were applied to a sample of ten patient plans in order to evaluate the impact of the calculated heterogeneity correction.
Results: Heterogeneity correction factors were computed for COMS plaque sizes ranging from 10 mm – 22 mm. Central axis dose correction varied from 10-12% up to 1 cm which matches previously published data. Off axis peripheral tumor doses varied up to 15% lower for the heterogeneous computation compared to the homogeneous computation.
Conclusion: Monte Carlo computed dose distributions in heterogeneous media provide a more accurate dose calculation than current methods. Heterogeneity correction factors should be used to evaluate the off axis doses for COMS eye plaques. While central axis doses vary 10-12%, peripheral doses evaluated from the patient sample indicate reduction in off axis dose targets. Consequently the use of heterogeneity correction factors results in improved accuracy in the calculation of dose to structures at risk.
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