There is a n increasing interest in radiotherapy as a pre or postoperative adjuvant to surgery i n the curative treatment of rectosigmoid cancer. This is a concept completely unrelated to palliative treatment, a n d therefore we need to understand the response of incidentally irradiated intestine in order that maximally curative doses of radiotherapy may b e used safely. There are two aspects of radiation injury: early mucosal injury and late fibrosis. W e have studied the acute response of colonic mucosa of the mouse to single a n d multiple doses of gamma rays. T h e radiosensitivity of colonic mucosal cells is similar to that of other cells of epithelial origin, both normal and neoplastic. TWO factors predominate i n the response of colonic mucosa to multifraction irradiation: A) the ability of cells to repair non-lethal radiation damage between dosefractions; and B) the regenerative capacity of surviving cells. We have studied these two aspects of the response of colonic mucosa a n d 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 d o not have direct proof, it is likely from available radiobiology studies that neoplastic cells a n d normal cells a r e equally capable of this repair. However, the normal mucosa possesses a great capacity for regeneration, a n d this is probably the mechanism that provides the radiotherapist with a margin of safety i n the postoperative treatment of residual small deposits of rectosigmoid cancer.
Cancer 345396-903, 1974.
HE NOTION T H A T THE CELLULAR RADIO-
T sensitivity of various malignancies was widely different, and that some varieties of tumor were intrinsically radioresistant delayed the effective use of radiation in their treatment. Examples of malignancies thought to be "radioresistant," but which have proven otherwise, include adenocarcinoma of the cervix, soft tissue sarcomas, clear-cell carcinomas of the uterine cervix, and carcinoma of the rectum. While i t is true that these tumors are unlikely to be radiocurable if they are large, the same is true of other malignancies now routinely and successfully treated by radio-