SU‐E‐T‐387: A Biologically Effective Dose Volume Histogram for Optimizing Eye Plaque Brachytherapy

Abstract

Purpose: Clinical optimization of eye plaque brachytherapy is currently limited to tumor coverage, standardized prescription dosage, and dose calculations to ocular structures. The biologically effective dose (BED) of brachytherapy treatments is a function of implant duration and chosen radionuclide. A novel method would propose to evaluate eye plaque brachytherapy implants based on BED delivered to the tumor volume and surrounding normal ocular structures.Methods: Using the equation introduced by Dale for temporary low dose rate (LDR) brachytherapy implants, 16 mm COMS‐eye plaque patient DVH data were converted to biologically‐effective dose volume histograms (BEDVH). These data were calculated for Pd‐103, I‐125, and Cs‐131 for different implant durations. Therapeutic ratios were derived from comparing BED results as a function of implant duration for tumors and normal ocular structures (lens, lacrimal gland, and optic nerve). Isobiologically‐effective physical doses were created for different implant durations and radionuclides. Results: The BEDVH curves were dependent on implant duration and less sensitive to radionuclide choice. In comparison to a 7‐day implant, maximum BED for a 1‐day implant increased by a factor of 2–3 for normal ocular structures; for the tumor, maximum BED increased by a factor of 4.5. These factors decreased with increasing implant duration, and were not significantly radionuclide‐dependent. Conclusions: A method was introduced to evaluate and further optimize eye plaque dosimetry through analysis of BED delivered to the tumor and adjacent normal tissue volumes. This method is readily adaptable to other temporary or permanent brachytherapy implants in a variety of clinical situations.