Effects of dose fractionation on late roentgen radiation damage of rat small intestine.

In female Wistar rats a 10 cm long exteriorized mid small intestinal segment was roentgen irradiated. Nominal standard radiation doses were 17 and 19 Gy, given as a single exposure and in 2 and 3 fractions with intervals of 48 hours. Animals were killed and examined in groups of 3 every 6 weeks from 8 to 44 weeks following irradiation. Macroscopic and histopathologic parameters of irradiation injury were used to calculate an injury score for each animal. In the 2 fractions group both mortality and irradiation injury score were higher than in the single exposure and 3 fractions groups. The difference was due in particular to persisting mucosal ulcerations and epithelial atypia. Adenocarcinoma of the irradiated intestine was found in 4 animals.