Late changes following single dose roentgen irradiation of rat small intestine.

In female Wistar rats a 10 cm long exteriorized mid small intestinal segment was roentgen irradiated with 17, 19, 21 and 23 Gy as single exposures. Animals were killed in groups of 3 at intervals of 6 weeks from 2 to 50 weeks following irradiation. Irradiation injury was assessed using 8 macroscopic and histopathologic parameters, and an injury score for each animal was calculated. The parameters used were divided in 2 subgroups, early and late alterations, showing different types of development. The score for the early alterations decreased from 2 to 20 weeks following irradiation and then remained constant. The late alterations increased and seemed to stabilize about 8 weeks following irradiation. After the initial 20 weeks there was no progression of irradiation injury.