A Comprehensive Dosimetric Evaluation of Circular Collaborative Ocular Melanoma Study (COMS) Plaques and Eye Physics Plaques On a Standard Eye Model
E Quan1*, B Teh2, A Schefler3, R Pino4, (1) UT MD Anderson Cancer Center, Houston, TX, (2) Houston Methodist Hospital, Houston, TX, (3) Houston Methodist Hospital, Houston, TX, (4) Houston Methodist Hospital, Houston, TX
Presentations
PO-GePV-T-22 (Sunday, 7/25/2021) [Eastern Time (GMT-4)]
Purpose: To evaluate dosimetric differences between circular COMS and Eye Physics (EP) plaques for uveal melanomas to provide clinical guidance in the selection of eye plaque for various tumor sizes and heights.
Methods: Tumors with basal diameters (D_base) ranging from 6mm to 18mm, and heights ranging from short (3mm) to tall (10mm), were simulated on the equator of a standard eye model in the Plaque Simulator planning system. Treatment plans with a COMS plaque selected based on the COMS convention and one or two EP plaques with similar diameter were calculated for each tumor. 85Gy was prescribed to tumor apex for tall tumors and prescribed to cover to at least tumor apex and 95% of the tumor base plus 2mm margin for short tumors.
Results: For short tumors, most EP plaques produce lower tumor base Dmax (Dmax_TB) and V85Gy of entire eye, and achieve similar coverage at shorter prescription height, than their corresponding COMS plaque, with an average reduction of 66Gy, 1.1%, and 0.7mm, respectively; this difference is more pronounced for D_base ≥ 12mm. For tall tumors with D_base > 14mm, EP and COMS plaques show similar Dmax_TB, but, with D_base ≤ 14mm, EP plaques reduce Dmax_TB by an average of 161Gy. However, for both short and tall tumors, EP plaques increase outside-of-margin Dmax (Dmax_OOM) by an average of 29Gy and 103Gy, respectively, although Dmax_OOM is on average 40% lower than Dmax_TB.
Conclusion: EP plaques generate lower max dose at tumor base, indicating potentially reduced ocular toxicity, compared to similar-sized COMS plaques, especially for tall tumors with small to medium base size and short tumors with medium to large base size. EP plaques do produce increased dose-spill outside of tumor, which should be carefully evaluated when tumor is located close to critical structures such as optic nerve and macula.
ePosters
Keywords
Eye Plaques, Dosimetry, Brachytherapy
Taxonomy
TH- Brachytherapy: Low Energy Seed Brachytherapy
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