Effect of Single and Divided Doses of X-Irradiation on Longevity in Rats

Abstract

Longevity in Long Evans-Wistar f/sub 1/ hybrid female rats was observed following 0, 120, 240, and 480 r total-body x irradiation administered in either single or divided exposures. Divided exposures consisted of either 3 or 6 equal fractions spaced at 3.5, 7, or 14 day intervals. Life span was significantly shortened by irradiation when the total dose was expressed on either a linear or logarithmic scale. The greater the dose the larger the life shortening even 120 r shortening life by 13 per cent. Increase of numbers of dose fractions from 3 to 6 significantly improved longevity. The protective effect of dose fractionation is dose dependent, being demonstrated at 480 and 240 r but not at 120 r. Spacing of dose fractions at 3.5, 7, or 14 day intervals did not influence longevity. Estimated regression coefficients indicate that fractionation of a dose in the 1, 3, 6 fraction range offers approximately 30 to 46% of the protection gained by reducing the total radiation dose by one haif in the 0, 120, 240, 480, r dose range. (auth)