Mammary Neoplasia in the Rat as Related to Dose of Partial-Body Irradiation

Abstract

Female Sprague-Dawley rats were exposed to 250-kvp X-rays at 42 days of age so that the anterior half of the animal received either 0, 222 R, 444 R, 666 R, 888 R, or 1110 R in a single exposure. The animals were studied over their entire life span. The life span was reduced increasingly with increasing dose. The non-exposed animals had similar rates of mammary neoplasia in the anterior and posterior areas. Mammary neoplasia was much more prevalent in the anterior, exposed area than in the posterior, shielded area. Within the anterior, exposed area the incidence of mammary neoplasia increased in an approximately regular manner as the dose was increased from 222 R to 88 8R. The mammary neoplastic response to 1110 R was less than the response to 888 R and often less than the response to 666 R when calculated on a rat-day at risk basis. The decline in mammary neoplastic response at 1110 R was thought to be the result of cell death of mammary tissue cells, some of which would have been expected to develop neop...