Radiation response of mammalian tumor cells. i. repair of sublethal damage in vivo

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.