Kinetics of regrowth of V79 spheroids after gamma- and pi--irradiation.

Spheroids of V79 cells were irradiated with 180 MeV/c pi--mesons in the peak region and with gamma-rays. Doses of 900 and 1500 rad were applied, respectively, yielding 14% surviving cells. Regrowth of the spheroids was followed by measuring volume changes, cell multiplication as well as viability and proliferation of cycling and resting spheroid cells. While volume growth after irradiation was equal for both radiations, the time profiles of cell density, viability and mean DNA content per cell were found to be different. Consistently, a more prompt and pronounced response to pion irradiation could be inferred and was discussed in terms of LET dependent proliferation and elimination of inactivated cells and their subsequent substitution by viable progeny cells. Recruitment of resting cells was observed with both radiations.