INDUCTION OF LUNG-TUMORS IN RFM MICE AFTER LOCALIZED EXPOSURES TO X-RAYS OR NEUTRONS

The purpose of the present study was to compare the dose-response relationships for the induction of lung tumors in RFM mice after localized thoracic exposures to X rays or fission neutrons. Animals were killed 9 months after localized irradiation, their lungs were cleared, and the tumors were counted to determine both percentage incidence and tumors/mouse. From these data, the relationship between tumors/mouse and X-ray dose could be described adequately by a linear-quadratic model with a shallow initial slope, or by a threshold model with a dose-squared response above the threshold dose, and linearity could be rejected over the dose range of 0 to 900 rad. For neutrons the relationship between tumors/mouse and dose over the range of 0 to 25 rad could be described by a linear, or a threshold model with linear response above the threshold. In either case, the relative biological effectiveness increased with decreasing neutron dose from 25 at 25 rad to 40 at 10 rad.