Background Episcleral brachytherapy is the most common eye-preserving treatment for medium-sized choroidal melanomas. γ-emitting iodine-125 (¹²⁵I) and β-emitting ruthenium-106 (¹⁰⁶Ru) 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 ¹⁰⁶Ru and 254 with ¹²⁵I. The rate of repeated brachytherapy was significantly higher among patients treated with ¹⁰⁶Ru (8%) than with ¹²⁵I (1%, p<0.001). Size-controlled Cox regression HRs for postbrachytherapy enucleation (¹²⁵I vs ¹⁰⁶Ru 0.7, p=0.083) and melanoma-related mortality were not significant (¹²⁵I vs ¹⁰⁶Ru 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 ¹⁰⁶Ru 59%, ¹²⁵I 56%) and ≥7.5 mm thick tumours (relative survival ¹⁰⁶Ru 46%, ¹²⁵I 44%).

Conclusions Rates of repeated brachytherapy were significantly higher among patients treated with ¹⁰⁶Ru versus ¹²⁵I for thick choroidal melanomas. There were, however, no significant differences in rates of enucleation or patient survival.