2768 - Brachytherapy for the Treatment of Ocular Melanoma: Comparing Yttrium-90 (Y90) to Palladium (Pd-103) and Iodine (I-125)

Purpose/Objective(s): The most commonly used radioactive isotopes for the treatment of ocular melanoma are Pd-103 and I-125. Recent novel studies have proposed the implementation of Y90 brachytherapy as an alternative. Y90 radiation is delivered via electrons with a single treatment, with advantages including technical aspects of administration and plan optimization. The purpose of this study is to assess the radiation doses to target and adjacent structures using Y90.

Materials/Methods: We performed a dosimetric comparison of Pd-103, I-125, and Y90 for patients treated at a single institution (2018-2024). We calculated mean dose and dose differences for critical adjacent structures using Kruskal-Wallis and Dunn’s Tests in R. Dose for Y90 was calculated based off previously validated metrics using percentage depth dose (PDD) published by the manufacturer. We also determined the percentage of patients who would qualify for Y90 treatment based on criteria including tumor size and height. Y90 applicators come in 2 sizes, 6mm and 10 mm, for which we used a margin of 1mm, and a target no thicker than 3 mm.

Results: 73 of 258 patients (28%) met criteria for treatment with Y90. Differences in the delivered dose to critical structures were significant. Y90 delivered higher mean dose to the inner sclera and lower doses to 5-mm depth, opposite retina, lens center, optic disc, and macula (p-value < 0.001) compared to tumors treated with Pd-103 and I-125 (Table 1).

Conclusion: Y90 brachytherapy is a practical alternative to traditionally used Pd-103 and I-125 implants for localized treatment of ocular melanoma. Based on dosimetric comparison, treatment with Y90 results in decreased radiation to adjacent structures. These results suggest Y90 may be a superior treatment option in appropriately selected patients with small tumors. Further research is required to validate these findings.