Chemical Protection against Long-Term Effects of Whole-Body Exposure of Mice to Ionizing Radiation: III. The Effects of Fractionated Exposure to C57B1 Mice

Mice of the C57B1/Cnb strain were exposed to four fractionated doses delivered at weekly intervals (total doses from 4 × 50 to 4 × 375 R). One group of mice received a mixture of radioprotectors. The animals were followed to their natural death and investigated for histopathology. Life-shortening showed a sigmoid dependency on the dose in nonprotected and protected mice with a dose reduction factor of 2.1 at 50% life-shortening. Thymic lymphoma was the most predominant cause of death in irradiated C57B1 mice. Radioprotectors diminished significantly the incidence of this disease but apparently did not reduce other causes of death. Reticulum cell sarcoma B also increased at the same low doses as thymic lymphoma. Both thymic lymphoma and reticulum cell sarcoma B increased in frequency after a fractionated dose compared to a single exposure with doses of 600-700 R and 300-400 R, respectively.