Comparative Effects of Fission Neutron and X Irradiation on 7.5-Day Mouse Embryos

Dl MAJO, V., BALLARDIN, E., AND METALLI, P. Comparative Effects of Fission Neutron and X Irradiation on 7.5-Day Mouse Embryos. Radiat. Res. 87, 145-158 (1981). Fission spectrum neutrons (0-46.5 rad) were compared with 250-kV X rays (0-200 rad) for reduction of fetal weight and for embryolethal and teratogenic effects in mice. Animals were irradiated 7.5 days postcoitum (p.c.) and fetuses were examined 18.5 days p.c. Mortality showed a definite shoulder for both types of radiation. The shoulder was smaller for neutrons than for X rays, and at 20% mortality, the dose ratio was approximately 3. The relative biological effectiveness (RBE) for weight loss was 3.2 ? 0.8. The dose-effect relationships for major malformations after X irradiation showed a large shoulder (approximately 100 rad), while no apparent threshold could be seen in the neutron series, so that the relative efficiency of neutrons was dependent on the neutron dose. The equal effectiveness dose ratio estimated at 7% incidence of severe external malformations was 2.4, increasing to about 3.4 if more common head abnormalities were also included. In conclusion, fission neutrons induce the same types of effects as X rays in 7.5-day mouse embryos, being two to four times more effective than sparsely ionizing radiation at relatively high doses, except for major malformations where the RBE is higher with decreasing neutron doses.