Intestinal Crypt Survival: The Effect of Cobalt-60, 250 kVcp X-Rays and Fission Neutrons

Intestinal crypt survival was studied using the method of Hagemann, Sigdestad and Lesher (8) in mice irradiated with 250 kVcp x-rays, cobalt-60 and fission neutrons. The D₀'s for the three treatment modalities were 377, 375 and 103 rads with extrapolation numbers of 6.2, 9.2 and 3.1, respectively. The RBE (ratio of D₀'s relative to x-rays) was 3.6 and 1.0 for neutrons and cobalt-60, respectively. The <tex-math>${\rm LD}_{50(5)}$</tex-math> values were found to be 1081 (945-1247), 1365 (1279-1456) and 252 (234-273) rads. The RBE [ratio of <tex-math>${\rm LD}_{50(5)}$</tex-math> relative to x-rays] values were found to be 4.3 and 0.8 for neutrons and cobalt-60 irradiation. Intestinal crypt survival varied from 25 to 34% of control at all of the <tex-math>${\rm LD}_{50(5)}$</tex-math> values. Total and per crypt cellularity was determined at 3 days postirradiation for each modality. The maximum proliferative response, measured at this time, occurred at or near the <tex-math>${\rm LD}_{50(5)}$</tex-math> dose for each type of radiation.