High dose rate and low dose rate ruthenium brachytherapy for uveal melanoma. No association with ocular outcome

Background Episcleral brachytherapy is the most common eye-preserving option for treating uveal melanoma, with ruthenium-106 widely used in Europe. Case series have reported on ocular outcome, but there are very little data on the impact of dose rate. Therefore, we studied the association of dose rate with secondary enucleation. Methods Data for all patients in Sweden managed with brachytherapy from 1979 to 2012 were retrieved (962 patients) and divided in quartiles based on dose rates at the tumour apex and at the scleral surface. Kaplan-Meier curves for secondary enucleation were generated independent of dose rate and for each dose rate quartile. Cox regression univariate and multivariate modelling included clinical parameters and dose rates at the tumour apex and the scleral surface. Results Baseline clinical characteristics were not significantly different across the quartiles except that thinner tumours had higher dose rates at the tumour apex. Dose rates ranged widely, with a near normal distribution at the scleral surface but skewed at the tumour apex. For all quartiles, secondary enucleation was more often caused by tumour progression than by ocular side effects. Univariate and multivariate modelling including clinical parameters showed no association between dose rate and secondary enucleation. Conclusions Although dose rates ranged widely, there was no apparent association with secondary enucleation, suggesting that based on ocular survival, current practice of annual replacement of applicators is acceptable, irrespective of the significant reduction in each applicator9s dose rate. Nevertheless, patients treated with higher dose rates have shorter plaque exposure and presumably less ocular irritation.