Radiation Response of Mammalian Tumor Cells. I. Repair of Sublethal Damage In Vivo 2

To answer certain questions concerning the ability of mammalian tumor cells to repair sublethal radiation damage in vivo , the 2-dose recovery response of the P388 lymphocytic tumor of the DBA/2 mouse was studied as a function of tumor age at the time of the conditioning dose. Aerobic (1-day) and hypoxic (6-day) tumors demonstrated early repair of sublethal damage; the rate of recovery was slower in 6-day tumors. In addition, the maximum degree of recovery in tumors of either age was of the same order of magnitude as the extrapolation numbers observed from single dose-survival curves. Complete recovery, i.e. , return of threshold response similar to that observed with nonirradiated cells, occurred within 24 hours after the conditioning dose.