Brachytherapy With 15- Versus 20-mm Ruthenium 106 Plaques Without Verification of Plaque Position Is Associated With Local Tumor Recurrence and Death in Posterior Uveal Melanoma

Abstract

Brachytherapy with episcleral plaques is the most common primary tumor treatment for uveal melanoma. This study aims to compare the risk of tumor recurrence and metastatic death between two frequently used ruthenium-106 plaque designs: CCB (20.2 mm) and CCA (15.3 mm). Data were obtained from 1387 consecutive patients treated at XXX between 1981 and 2022 (439 with CCA and 948 with CCB plaques). During the period, scleral transillumination was performed to delineate tumor margins before plaque insertion, but no minimum scleral dose was used, and accurate plaque positioning was not verified after scleral attachment. Patients treated with CCA plaques had smaller tumors than those treated with CCB plaques (mean diameter 8.6 vs. 10.5 mm, P<0.001). There were no differences in patient sex, age, tumor distance to the optic disc, tumor apex dose, dose rate, or in rates of ciliary body involvement, eccentric plaque placement, or adjunct transpupillary thermotherapy. The average difference between plaque and tumor diameter was greater with the CCB plaque, and a smaller difference was an independent predictor of tumor recurrence. The 15-year incidence of tumor recurrence was 28% and 15% after treatment with CCA and CCB plaques, respectively (competing risk analysis, P<0.001). Multivariate Cox regression analysis revealed a lower risk for tumor recurrence with CCB plaques (HR 0.50). Similarly, patients treated with CCB plaques had a lower risk for uveal melanoma-related mortality (HR 0.77). Adjunct transpupillary thermotherapy did not reduce these risks. Uni- and multivariate time-dependent Cox regressions demonstrated that tumor recurrence was associated with uveal melanoma-related and all-cause mortality. Compared to 20 mm plaques, brachytherapy with 15 mm ruthenium plaques is associated with a higher risk for tumor recurrence and death. These adverse outcomes may be avoided by increasing safety margins and implementing effective methods to verify accurate plaque positioning.