Radiation Dose–Volume Effects of Optic Nerves and Chiasm

Selected data from used to compare incidence of radiation-induced optic neuropathy (RION) vs. maximum dose (Dmax) to optic nerves. Selected studies generally used fraction sizes with range of 1.8–2.0 Gy, assessed the dose to the nerve directly from their best estimate of dose distribution in the structure (i.e., not as a partial volume average), did not include pituitary lesions (lower tolerance), and selected patient age <70 years (if segregated). Bars illustrate range of doses for groups characterized by incidence values. Points offset from 0% to ≤1% were shifted to clearly show range bars. For points displayed at 0%, available range information was outside 50–70 Gy. Threshold for RION appears to be 55–60 Gy. However, range bars illustrate treatment in 60–65 Gy range for some studies without RION. Data estimated from tables, figures, and text reported in the studies, because exact incidence data were not always provided. The 1 patient in the study by Parsons et al. (4) with an event in the 55–60-Gy range was treated to 59 Gy. The 1 patients with an event in the study by Martel et al. (14) in the 55–60-Gy range received 59.5 Gy.

Isoeffect linear-quadratic model extrapolations and alternative biologically effective threshold models (curves) compared with reported maximum optic nerve/chiasm doses detailing incidence of radiation-induced optic neuropathy (RION) (symbols) for full range of dose per fraction. Linear-quadratic model was unreliable for extrapolating from fractionated (1.8–2.0-Gy/fraction) dose range to single-fraction range. Detailed data needed for low (<1.8 Gy) and hypofractionated regions to better define organ response.