Survival of Mice Under Duration-of-Life Exposure to Gamma Rays. I. The Dosage-Survival Relation and the Lethality Function<xref ref-type="fn" rid="FN2">2</xref>

Abstract

Survival data were obtained on 5,052 mice given Co60 gamma radiation for the duration-of-life starting at 100 days of age. There were 36 treatment levels, and daily doses ranged from 5 to 200,000 r per day, with mean after-survival times ranging from 500 to 0.25 days. Daily doses of 2500 r per day or less (survival greater than 5 days) were given over a 12- to 15-hour period every day, and higher daily doses over 24 hours with minimal interruption. Dosimetry procedures and errors are fully discussed. The data for survival times of 60 days or less are analyzed in terms of a previously described plot of reciprocal of daily dose (as ordinate) versus mean after-survival time, which has the dimension of accumulated lethal injury per unit daily dose. Four distinct phases of injury are identified, centered at 0.5, 5, 13, and 40 days. These phases can be related to four different modes of physiological injury—to the central nervous system, the gut epithelium, the leukopoietic system, and the erythropoietic system, respectively. A great sex difference in survival times for survivals ranging from 20 to 40 days is revealed. For mean after-survival in excess of 60 days, the plot of logarithm of mean after-survival versus daily dose is very nearly linear, so coefficients of life shortening can be estimated with uncertainties of, at most, a few percent. Despite a sex difference in control survival there is no sex difference in the coefficients of days lost per roentgen. The relation of these results to the results from single-dose, split-dose, and fractionated exposure is discussed, and current mathematical theories are critically examined.