Induction of Chromosomal Aberrations and Sister Chromatid Exchanges by Alpha Particles in Density-inhibited Cultures of Mouse 10T½ and 3T3 Cells

Summary

We examined the dose—response relationships for the induction of cell killing, chromosomal aberrations and sister chromatid exchanges (SCE) by 220 kV X-rays and 5·3 MeV alpha particles from a ²³⁸Pu source. The cells were irradiated in density-inhibited, confluent cultures. The D₀ values for the X-ray and alpha particle survival curves were 1·7 Gy and 0·7 Gy, and the extrapolation numbers 2·5 and 1·0, respectively, for mouse 3T3 cells. Chromosomal aberrations increased linearly with dose for alpha-radiation and roughly with the square of dose for X-rays in 3T3 cells. At 37 per cent survival, 1·0 chromosomal aberration per cell was induced by X-rays and 1·7 per cell by alpha-radiation, but the fraction of cells without aberrations was similar. In confluent holding recovery experiments there was a 50 per cent reduction in X-ray-induced aberrations during the first 4 h of confluent holding. No decline in alpha-induced aberrations was observed with holding times up to 24 h. The dose—response relationship for the induction of SCE by X-rays increased linearly with doses up to 100 cGy in both 3T3 and 10T½ cells, then declined, reaching nearly background levels after 400 cGy. The induction of SCE increased rapidly in these cell lines with doses of 2·5–5·0 cGy of alpha-radiation, then declined. The relative biological effectiveness (RBE) was 15–25 for the induction of SCE by low doses (2·5–5·0 cGy) of alpha particles.