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

A model for quantitating late effects of x-radiation 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 at the Clinton P. Anderson Meson Physics Facility, Los Alamos Scientific Laboratory, Los Alamos, New Mexico. The endpoint involves microscopic evaluation of the severity of the experimental lesion, compared with surgically resected bowel lesions we have 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 four and 12 months after completion of radiation exposures.