The Effect of Whole-Body X-Irradiation on the Median Lifespan of Female Dogs (Beagles)

Median survival time (MST) and major causes of death were determined for 360 control and x-irradiated female beagles. At 10 to 12 months of age the beagles were given single or fractionated x-ray (250-kVp) exposures totaling either 100 R or 300 R. Thereafter they were maintained in outdoor pens for lifetime studies. Most deaths occurring during the first 3 years postirradiation appeared to be due to synergism between the effects of environmental stresses and x-irradiation. In the final analyses, all irradiated beagles exhibited life-span shortening relative to controls: 9.5% and 20.7% for the 100-R and 300-R groups, respectively. On a linear scale this represented a loss of 6.7% per 100 R. Differences between subgroups receiving fractionated exposures were apparent only at 300 R, where life-span shortening was reduced when the elapsed time between first and last exposure was increased from 7 to 84 days. Mortality rates could be fit to the Gompertz equation only during the last 6 years of life. The Gompert...