Ruthenium-106 versus iodine-125 plaque brachytherapy of 571 choroidal melanomas with a thickness of ≥5.5 mm

Background Episcleral brachytherapy is the most common eye-preserving treatment for medium-sized choroidal melanomas. gamma-emitting iodine-125 (I-125) and beta-emitting ruthenium-106 (Ru-106) are widely used. The latter is however generally reserved for thinner tumours (<6 mm). In this study, we compare ocular and patient survival in thicker tumours treated with the respective radioisotope. Methods All patients with >= 5.5 mm thick choroidal melanomas who were treated with plaque brachytherapy at a single institution between 1 November 1979 and 31 December 2015 were included (n=571). Size-controlled Cox regression HRs for postbrachytherapy enucleation, repeated brachytherapy and melanoma-related mortality were calculated, as well as Kaplan-Meier disease-specific survival and relative 10-year survival in matched subgroups. Results 317 patients were treated with Ru-106 and 254 with I-125. The rate of repeated brachytherapy was significantly higher among patients treated with Ru-106 (8%) than with I-125 (1%, p<0.001). Size-controlled Cox regression HRs for postbrachytherapy enucleation (I-125 vs Ru-106 0.7, p=0.083) and melanoma-related mortality were not significant (I-125 vs Ru-106 1.1, p=0.63). Similarly, Kaplan-Meier disease-specific and relative 10-year survival was comparable in matched groups of 5.5-7.4 mm (relative survival Ru-106 59%, I-125 56%) and >= 7.5 mm thick tumours (relative survival Ru-106 46%, I-125 44%). Conclusions Rates of repeated brachytherapy were significantly higher among patients treated with Ru-106 versus I-125 for thick choroidal melanomas. There were, however, no significant differences in rates of enucleation or patient survival.