Acute reactions of the lip mucosa of mice to fractionated irradiations.

The acute reaction of the lip mucosa of mice after single and fractionated irradiations has been investigated. The mouths of 24 mice were irradiated simultaneously in a single field. It was found that the acute reaction of lip mucosa can easily and reliably be scored. The variation in scoring between different observers is small and the reaction is reproducible. The mucosal reaction starts at day 7, reaches a maximum at about day 11-12 and regresses rapidly during the following 6 to 7 days. The overall reaction period is thus shorter for lip mucosa than for skin in the mouse, indicating a shorter cell cycle time. Dose-response curves can be constructed by plotting the average reaction from day 8 to 17 versus the total dose. The curve of log isoeffect dose for an average reaction level 3 against log number of fractions has a slope of 0.35 for a dose rate of 200 cGy/min and 0.29 for 33 cGy/min. The dose required to induce focal mucosa desquamation is significantly lower than that necessary to produce spotted epidermolysis in skin (16.5 Gy vs. 33 Gy for single dose).