Late Effects of Fractionated X-Irradiation in Mice. Failure to Prevent Nonthymic Lymphomas by Thigh-Shielding

Abstract

Groups of female LAF1 mice were exposed to an X-ray dose of 260 rads given in a single dose (at 11 weeks or 14 months of age) or in 52 weekly doses of 5 rads each (started at 11 weeks of age). A group of the latter animals had 1 thigh shielded during irradiation. The incidence of generalized nonthymic malignant lymphoma increased in both groups receiving fractionated doses of radiation; thigh-shielding did not inhibit leukemogenesis. This suggests that the mechanisms of radiation induction of thymic and nonthymic lymphomas in mice may differ, since, in the former case, shielding of hematopoietic cells reduces lymphoma incidence. Median life span did not differ significantly among the groups of mice irradiated at 11 weeks of age. The median life span for the mice receiving a single dose of 260 rads at 14 months of age was 28 months, five months longer than that of the group receiving a single dose of 260 rads at 11 weeks of age.