Rat Skin Tumor Incidence Following Single and Fractionated Exposures to Proton Radiation

Abstract

Experiments were conducted to establish the dose-response curve and degree of split-dose recovery for tumor induction and hair follicle survival in rat skin irradiated with protons. A proton beam from a cyclotron was modified to provide an approximately linear decrease in dose with depth in tissue to a maximum of about 1.3 mm. Six doses were given in the range from 75-750 rad. The tumor yield at 100 wk after irradiation increased as D2.8. Split doses consisted of an initial dose of 150 rad followed 24 h later by graded doses in the range from 150-600 rad. Split doses produced a sparing effect on follicle killing and yield of tumors. The magnitude of the reduction in tumor yield was consistent with complete recovery. Comparisons with previous results indicated that protons were 2.0-2.4 times as effective as electrons for tumor induction and the shapes of the dose-response curves were similar.