Dose-response of critical structures in the posterior eye segment to hypofractioned stereotactic photon radiotherapy of choroidal melanoma

Purpose: To identify modifying factors and dose-/volume-response relationships for the retina and optic nerve related to highly conformal hypofractionated radiotherapy. Patients and methods: Seventy-three patients undergoing hypofractionated stereotactic photon radiotherapy of choroidal melanoma were included in this retrospective study. The volumes of the optic nerve receiving doses of more than 7.5 or 12 Gy, respectively, were defined. Optic nerve circumference included in the 30%, 40%, 50%, or 80% isodose (ON%) and retina included in 30% or 40% were determined as quantal effects. Univariate and multivariate analyses were performed for clinical variables as well as probit analysis to define EDx (doses where a positive response is expected in x% of the cases). Results: Median follow-up was 90.0 (interquartile range 69.0-98.0) months. Fifty-two (71%) and 49(67%) patients developed radiation retinopathy and optic neuropathy (any grade). Age, length of follow-up and diabetes were significant parameters regarding retinopathy. Optic neuropathy was significantly influenced by age, length of follow-up, and ON30. The probability of optic neuropathy (any grade and grade >= 2) significantly increases with the dose (p ranges from 0.0126 to 0.0211). Conclusion: Treatment planning should aim at minimizing encompassing isodoses particularly in the low dose region, without compromising PTV coverage. (C) 2013 Elsevier Ireland Ltd. All rights reserved.