Drastic G 2 Arrest in Mammalian Cells after Irradiation with Heavy-Ion Beams

Abstract

Unsynchronized exponentially growing V79 monolayer cultures were exposed to high-energy accelerated heavy-ion beams (/sup 12/C, /sup 20/Ne, /sup 40/Ar) at various positions in their unmodified Bragg ionization curves. High-LET particle beams proved to be much more effective in causing a G/sub 2/ + M block, measured by the method of flow microfluorometry, than low-LET radiation. The number of cells arrested in G/sub 2/ + M increased linearly with dose up to at least 75% of the maximum effect. In this domain, the RBE values were LET-dependent with a maximum (RBE/sub 50/ = 8.3) at about 100 keV/..mu..m. In contrast to ..gamma.. and x rays, heavy ions with high LET did not affect cell traverse through the G/sub 1/ and S phase. Though the RBE values for G/sub 2/ + M block are much higher than the RBEs for survival, there was a linear relationship between accumulation of cells in G/sub 2/ + M and cell killing.