Effects of argon ions on synchronized Chinese hamster cells

The results of variation in radiosensitivity within the cell cycle of cultured Chinese hamster cells (line CHO) after exposure to argon ions compared to x rays are reported. The cells were first synchronized by mitotic selection and resynchronized in the region of late G1/early S phase by treatment with hydroxyurea (10/sup -3/ M). A fixed argon-ion dose of 400 rad at the distal end of a ridge-filter-modified Bragg peak or a 150-kVp x-ray dose of 900 rad was used to expose cells at different stages in the cell cycle. The results indicate that the variation (ratio of maximum survival tominimum survival) was approximately 25-fold for x rays, whereas there were no significant variations within the cell cycle for argon ions. Complete cell-survival curves also were obtained for argon ions and x rays at the G1/S boundary and in late S phase. No significant difference in radiosensitivity for argon ions was observed between these two cell phases. The RBE for late S cells decreased rapidly with increasing dose, whereas the RBE for cells at the G1/S boundary appeared independent of dose. At a therapeutically relevant dose per fraction of 200 rad, the RBE values for argon ions for cells at the G1/S boundary and in late S phase were 1.7 and 9.8, respectively