Late radiation enteropathy following split-dose irradiation of rat small intestine.

In female Wistar rats roentgen irradiation of a 10 cm long exteriorized mid small intestinal segment was performed. The radiation dose was 23 Gy, given as a single exposure or divided in two equal fractions separated by intervals of 4 to 96 hours. Radiation injury was assessed 2, 8 and 26 weeks following irradiation using a semiquantitative histopathologic scoring system. An increased fractionation interval led to a reduced degree of radiation injury at all 3 observation times. The greatest difference was found between the single dose and 4 hour groups, indicating a relatively large capacity for repair of sublethal damage. The degree of radiation injury also decreased significantly when the interval between fractions was increased from 4 hours to 96 hours. This suggests that the phenomenon of slow repair may occur in cells involved in the development of late radiation enteropathy. However, an indirectly protective effect due to mucosal repopulation between fractions may also explain some of the differences.