Visual outcome after posterior uveal melanoma episcleral brachytherapy including radiobiological doses

Abstract

Purpose: To assess the long-term influence of radiobiological doses in the evolution of visual acuity (VA) in patients with uveal melanoma treated by episcleral brachytherapy.

Material and methods: Visual acuity was evaluated prospectively from a case series of 243 patients in 2016 treated with ¹²⁵I. Data analysis was applied to trend VA outcome and find the accurate best-fit line. Biologically effective dose (BED) was included in survival analysis with the use of Kaplan-Meier and Cox regressions. Hazard ratio (HR) and confidence interval at 95% (CI) were determined. Variables statistically significant were analyzed and compared by log-rank tests.

Results: The median follow-up was 74.2 months (range, 3-223). Exponential regression shows a 25% reduction and 50% in visual acuity score (VAS) scale for 5 and 27.8 months, respectively. Cumulative probabilities of survival analysis were 57%, 42%, 27%, and 23% at 3, 5, 10, and 15 years, respectively. Multivariable analysis found tumor height (HR = 1.18, 95% CI: 1.07-1.29), applicator size (HR = 1.22, 95% CI: 1.08-1.36), juxtapapillary localization (HR = 1.70, 95% CI: 1.01-2.84), and dose to foveola (HR = 1.01, 95% CI: 1.00-1.01) significantly associated with VA loss. Log-rank tests were significant for all those variables. BED has a strong influence in univariate model, but not statistically significant in the multivariate one.

Conclusions: Visual acuity changes can be modeled by an exponential function for the first 5 years after treatment. No relation between VA loss and BED has been found; nevertheless, apical height, plaque size, juxtapapillary localization, and dose to fovea were found as statistical significant variables.

Keywords: brachytherapy; plaque brachytherapy; radiobiological doses; radiobiology; uveal melanoma.

Fig. 1

Scatterplot and fitted regression line. Presentation of the mean Δ(T) and quarter, T, after brachytherapy for 5 years

Fig. 2

Actuarial Kaplan-Meier, curve in blue, for the event VAS ≤ 50. Values at 95% CI are in red. Mortality Table is below. N is the number of patients at risk and SP is the survival probability (%)

Fig. 3

Kaplan-Meier cumulative survival functions (CSF) for the event VAS ≤ 50. The curves in each of the graphs are not overlapping and there is statistically significant difference between the for the variables tumor height, plaque size, juxtapapillary localization and dose to fovea by log-rank test (p < 0.05). For survival tables N is the number of patients in the time interval and SP is the survival probability in %