Anatomical outcome after brachytherapy with bi-nuclide (Ru-106/Iodine-125) plaques in large uveal melanomas.

Background: Proprietary bi-nuclide plaques combine the radiation properties of beta and gamma brachytherapy and can irradiate a larger target volume compared to ruthenium-plaques. While reducing the dose to structures outside the target volume, brachytherapy with bi-nuclide-plaques (BBNP) delivers a higher target dose compared to iodine-plaques. We aimed at analyzing the local tumor control and eye retention probability after BBNP.

Methods: All consecutive cases with large uveal melanoma (tumor thickness ≥ 7 mm) treated with BBNP at our institution between 01/1999 and 12/2020 were included (n = 576, median follow-up: 30.8 months [interquartile range, IQR: 12.9-57.4]). Univariable and multivariable Cox regression analyses were performed.

Results: Secondary enucleation (SE) was performed in 13.5% of cases (n = 78) after the median of 20.0 months (IQR: 9.0-34.7) post-BBNP. The overall rate of local tumor recurrence (LR) in the cohort was 8.5% (n = 49) and was diagnosed at the median post-BBNP interval of 20.0 months (IQR: 15.6-35.2). Of the patients' baseline characteristics, higher age (> 67 years, adjusted hazard ratio [aHR] = 1.80, p = 0.011), tumor thickness (> 8.5 mm, aHR = 2.20, p = 0.002), visual acuity (> 0.5 logMAR, aHR = 1.83, p = 0.009), and sclera dose (> 1000 Gy, aHR = 1.65, p = 0.034) were independently associated with the risk of SE. In turn, higher age (> 67 years, aHR = 1.93, p = 0.023), tumor thickness (> 8.5 mm, aHR = 2.02, p = 0.020), and visual acuity (> 0.5 logMAR, aHR = 2.27, p = 0.005) were independently related to LR.

Conclusions: BBNP facilitates eye retention in 86.5% of patients with large uveal melanoma 2.5 years after treatment. Patients' baseline, tumor and treatment characteristics were strongly associated with the risk of SE and LR after BBNP.