Post-irradiation kinetics of the C3H/He mouse mammary carcinoma as regards tumor volume regrowth time and cell loss.

The reoxygenation kinetics of the third generation C3H/He mouse mammary carcinoma has been studied and related to the time for 50% of irradiated tumors to regrow to the initial volume at irradiation (TRT-50) and to changes in tumor cell numbers. The experimental results suggest the following conclusions: (1) Fluctuations in TRT-50 values after two-dose irradiation under aerobic conditions are due to reoxygenation. (2) Since the TRT-50 after a second irradiation under hypoxic conditions remains independent of intervals between two doses for at least 3 days, repopulation and synchronization of surviving cells between irradiations is minimal. (3) A decreased cell number and/or cell loss from irradiated tumors is an important factor in tumor reoxygenation.