Eyes wide shut.

A large pooled analysis in the Red Journal reports rates of radiation induced optic neuropathy (RION) with normal tissue complication probability modeling (NTCP). A major challenge with this is defining what RION is in the first place--most report it as a clinically significant decline in visual acuity or visual fields after radiation, but there’s no clear cut definition. What is clear cut: 1997 was a watershed year for RION (blame it on The Kid), with close to 10% rates of RION pre-97 compared to 1-2% post-97. Further analysis of the post-97 data indicates that 12 Gy max dose in a single fraction is the best predictor of RION with a rate of <1% @ <12 Gy and 5-10% @ >12 Gy. The biggest risk factor was prior irradiation, increasing the risk 10-fold even with conservative doses to the optic structures. TBL: NTCP modeling shows that a max dose of 12 Gy in 1 fraction, 20 Gy in 3 fractions, or 25 Gy in 5 fractions to radiation-naive optics confers about a 1% risk of RION.