Radiation tolerance of the optic pathway in patients treated with proton and photon radiotherapy

Introduction: Radiation-induced optic neuropathy (RION) is a complication of radiation therapy (RT) that causes blindness. We aimed to define the tolerance of the anterior optic pathway to fractionated RT and identify risk factors for RION. Materials/methods: Patients with chordoma or chondrosarcoma of the skull base treated with proton and photon therapy between 1983 and 2013, who received a minimum of 30 Gy (relative biologic effectiveness [RBE]) to the anterior optic pathway were assessed. Optic neuropathy with radiographic correlation occurring >= 6 months after completion of RT in the absence of tumor recurrence or other probable cause was diagnosed as RION. Results: Of 514 patients, 17 developed RION. With median follow-up of 4.8 years, cumulative incidence of RION was 1% among patients receiving <59 Gy (RBE) and 5.8% among patients receiving >= 60 Gy (RBE) to the optic pathway. Higher maximum point dose to the optic pathway (subhazard ratio [SHR] = 1.2, 95% CI 1.05-1.2, p = 0.001), older age (SHR = 1.1, 95% CI 1.02-1.08, p < 0.0005), and female sex (SHR = 16.3, 95% CI 2.2-122.4, p = 0.007) were statistically significant risk factors for RION in multivariate analysis. Conclusion: In our study cohort, rates of RION were very low with conventionally fractionated RT up to 59 Gy. At doses >= 60 Gy, there is an increased risk of RION, with greater risk for women and older patients. (C) 2018 Elsevier B.V. All rights reserved.