Quantitation of the late effects of X‐radiation on the large intestine

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Abstract
A model for quantitating late effects of x-irradiation on the large intestine utilizing the rectum of the Sprague-Dawley rat is reported. This model was constructed prefatory to establishing relative biological effectiveness for negative pions as a component of preclinical trials. The endpoint involves microscopic evaluation of the severity of the experimental lesion, compared with surgically resected bowel lesions studied following clinical radiation exposure of the bowel. Individual components of the overall lesion include mucosal ulceration, atypical epithelial regeneration, colitis cystica profunda, fibrosis and vascular sclerosis. Dose response curves were established for animals receiving 1, 2, 5 and 10 fractions with groups sacrificed at both 4 and 12 mo. after completion of radiation exposures. [Since the intestine is unavoidably exposed during radiation treatment of many abdominal and pelvic neoplasms, this organ assumes particular importance in terms of potential late complications of therapy.].