RBE of spleen CFU-S to low dose rate Cf-252 or photon radiation in vivo

The biological effects of low dose rate (LDR) Cf-252 radiation were compared to LDR Cs-137 photon radiation and acute 60Co radiation. The RBEn for endogenous CFU-S in vivo was 2.1 for neutron radiation at a dose rate of 9.9 cGy/hr of Cf-252 radiation. The value was consistent with previous in vitro experiments where a value of 2.1 was found. For the low doses and low dose rates studied, we tested an acute assay dose following the LDR irradiation to determine dose-effect and RBEn. Organ size shrinkage and regeneration patterns after LDR Cf-252 and Cs-137 were also studied and showed greater growth delay for Cf-252 irradiated lympho-hemopoietic tissues.