Observation of free radicals in skin fold window chamber model, prior to and after radiotherapy. (A) Fluore scence intensity of ROS sensitive dye is detectable prior to radiotherapy, but the level of fluorescence increases 24h after radiotherapy. This suggests some baseline level of oxidative stress that increases after radiotherapy. Administration of an SOD mimetic inhibits the increase in free radical production after radiotherapy (B) Administration of SOD mimetic inhibits increase in HIF-1-GFP expression and causes significant vascular damage, as observed at 48h after treatment. Modified from Moeller et al.8, with permission from the publisher. Bar, 300 μm.