The kinetics of recovery in irradiated colonic mucosa of the mouse

There is an increasing interest in radiotherapy as a pre or postoperative adjuvant to surgery in the curative treatment of rectosigmoid cancer. This is a concept completely unrelated to palliative treatment, and therefore we need to understand the response of incidentally irradiated intestine in order that maximally curative doses of radiotherapy may be used safely. There are two aspects of radiation injury: early mucosal injury and late fibrosis. We have studied the acute response of colonic mucosa of the mouse to single and multiple doses of gamma rays. The radiosensitivity of colonic mucosal cells is similar to that of other cells of epithelial origin, both normal and neoplastic. Two factors predominate in the response of colonic mucosa to multifraction irradiation: A) the ability of cells to repair non‐lethal radiation damage between dose‐fractions; and B) the regenerative capacity of surviving cells. We have studied these two aspects of the response of colonic mucosa and other cell renewal systems and shall discuss our results. Briefly, the capacity of colonic mucosa to repair nonlethal damage is similar to that of other epithelial cells. Although we do not have direct proof, it is likely from available radiobiology studies that neoplastic cells and normal cells are equally capable of this repair. However, the normal mucosa possesses a great capacity for regeneration, and this is probably the mechanism that provides the radiotherapist with a margin of safety in the postoperative treatment of residual small deposits of rectosigmoid cancer.