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Optic Disc and Macula Dose Estimation Without Dose Calculations in Ocular Brachytherapy Using 125I Standard COMS Plaques

S Lin*, Y Lee, Y Kim, The University of Arizona, Tucson, AZ


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: The purpose of this study is to generate comprehensive domestic data for optic disc and macula doses in ocular brachytherapy using 125I Collaborative Ocular Melanoma Study (COMS) plaques to allow clinicians in our institution to estimate optic disc and macula doses without dose calculations in a treatment planning system (TPS).

Methods: An in-house brachytherapy dose calculation program utilizing the American Association of Physicists in Medicine Task Group-43U1 formalism with a line source approximation was developed and validated against benchmark calculations in the literature. Then optic disc and macula doses were calculated as a function of distance from tumor margin (DT and MT) for various basal dimensions (BD and BM) for six (12 mm - 22 mm in diameter in 2 mm increments) COMS plaques loaded with 125I (model IAI-125A) seeds. A prescribed dose of 85Gy was normalized at a central-axis depth of 5 mm. Calculations were repeated for different prescription depths (1 mm - 10 mm in 1 mm intervals). Dose conversion factors to estimate optic disc and macula doses for different prescription depths were obtained by taking ratios of air kerma strength at the different prescription depths to that at 5 mm.

Results: The in-house program demonstrated similar accuracy to commercial TPS and Monte Carlo codes. Optic disc dose decreased as DT and BD increased. Similar patterns were observed for macular dose. Plaque size determined optic disc and macular doses and the shape of dose curves. Dose conversion factors decreased with increasing prescription depth. Also, the factors increased with increasing plaque size for a prescription depth <5 mm but the opposite was observed for a depth >5 mm.

Conclusion: The clinical data generated in this study will be beneficial in our clinical practice to predict optic disc and macula doses without dose calculations in a TPS.


Brachytherapy, Eye Plaques, I-125


Not Applicable / None Entered.

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