2718 - Larger ¹²⁵ I Radiotherapy Plaque Outcomes for Choroidal Melanoma: A Single Institution Retrospective Study

Purpose/Objective(s): Choroidal melanoma is the most common primary intraocular malignancy in adults. The COMS trial established globe-sparing therapy with ¹²⁵I plaque brachytherapy as a standard of care for small to medium-sized tumors. While plaques in COMS were available up to 20 mm in size, only 16% of tumors were 14 mm or greater. Limited data exists for larger plaque radiotherapy outcomes. This study aims to report clinical outcomes for patients with larger choroidal melanoma treated with ¹²⁵I brachytherapy. We hypothesize that ¹²⁵I brachytherapy provides effective local control and acceptable toxicity profiles in select patients using large eye plaques.

Materials/Methods: Patients diagnosed with choroidal melanoma between 2005 and 2024 treated with ¹²⁵I brachytherapy using standard COMS 20mm to 22mm plaque sizes were included. Tumor characteristics, ocular anatomy, radiation parameters, and outcomes were extracted from electronic medical record (EMR). Monte Carlo-based dosimetry was used to generate dosimetric parameters. Kaplan-Meier statistics estimated overall survival, local control, and metastases-free survival. Univariate analysis was performed using Cox proportional hazards regression to examine associations between ocular structure doses and adverse events.

Results: 175 patients were included. Baseline characteristics are presented in Table 1. The most common prescription dose was 85 Gy (88%), prescribed to a median depth of 6 mm (IQR: 5 to 7). Median follow up was 8.9 years (IQR: 2.3 to 9.3) and median survival was 9.6 years (CI: 7.2 to 12.8). The 10-year overall survival and metastases free survival was 49% and 62%, respectively. The 10-year local recurrence free survival was 87%. Nineteen (11%) patients underwent enucleation, with 8 (42%) for recurrence and 11 for RT complications including intraocular hemorrhage (3), persistent pain (3), progressive neovascularization (2), retinal detachment (2), or excessive inflammatory response (1). 5-year cumulative incidence of visual acuity decrease of 2 Snellen lines was 77%. Higher doses to ocular structures (ocular disc point and max dose, lens point dose) were associated with higher rates of adverse ocular effects including decreased visual acuity, cystoid macular edema, and radiation maculopathy.

Conclusion: 125I plaques of 20 and 22 mm resulted in favorable local control and metastasis-free survival. Higher doses to critical ocular structures were associated with increased toxicity. These findings support the role of ¹²⁵I brachytherapy as an alternative to enucleation for large tumors, with implications for personalized treatment planning to balance tumor control and vision preservation.