Survival and kinetic response of V79-spheroids after exposure to heavy ion beams.

Multicellular V79-spheroids and V79-monolayer cultures were irradiated with charged particle beams. The beams studied and their initial extraction energies were carbon (400 MeV/amu), neon (425 MeV/amu) and argon (570 MeV/amu). Survival was measured at a position in the plateau, and at a position in the middle of a 4 cm extended Bragg peak. Relative biological efficiency (r.b.e.) values for survival of spheroid cells at peak positions were high (4.1--4.2) in comparison to those obtained with monolayer cultures (1.8--2.4) of the same cell line. This finding is explained by the fact that three dimensional cell contact, which benefits survival after low LET radiation, does not influence survival after heavy ion irradiations in the Bragg peak. The peak-plateau r.b.e.-ratio was most advantageous for the carbon-ion beam (= 4.2). Whereas non-cycling inner spheroid cells showed hardly any kinetic changes up to 24 hours after heavy ion irradiation, outer cycling spheroid cells were arrested in G2 + M within a few hours after exposure.