ON THE SHAPE OF NEUTRON DOSE-EFFECT CURVES FOR RADIOGENIC CANCERS ANDLIFE SHORTENING IN MICE

Male and female hybrid BCF1 (C57BL/6 BdxBALB/c Bd) were exposed to tot al neutron doses of 0.06, 0.12, 0.24, and 0.48 Gy in fractions over a period of 24 weeks. The fractionation regimens were: 24 weekly fractio ns of 0.0025 Gy, 12 fractions of 0.01 Gy every 2 weeks, 6 fractions of 0.04 Gy every 4 weeks, and 3 fractions of 0.16 Gy every 8 weeks. In o rder to detect any change in susceptibility with age over the period o f exposures from 16 weeks to 40 weeks of age, mice were exposed to sin gle doses of 0.025, 0.05, 0.10, and 0.2 Gy at 16 and 40 weeks of age. These experiments were designed to test whether the initial parts of t he dose-response relationships for life shortening and cancer inductio n could be determined economically by using fractionated exposures and whether or not the initial slopes were linear. The conclusions were t hat for life shortening and most radiogenic cancers, the dose-effect c urves are linear and that fractionation of the neutron dose has no eff ect on the magnitude of the response of equal total doses over the ran ge of doses studied. The ratio of such initial slopes and comparable l inear initial slopes for a reference radiation should provide maximum and constant relative biological effectiveness values.