Analysis of bystander effect induced by heavy ions and -rays; Its dependencies on radiation quality and post-irradiation culture time

Yokota, Yuichiro; Funayama, Tomoo; Ikeda, Hiroko; Muto, Yasuko*; Suzuki, Michiyo; Sakashita, Tetsuya; Kobayashi, Yasuhiko

We investigate radiation-induced bystander effect to elucidate its mechanism. Cells irradiated with up to 2 Gy of carbon ions (108 keV/m) and -rays (0.2 keV/m) were co-cultured with non-irradiated cells in the above and below of porous membrane. Non-irradiated bystander cells decreased their survival at 6 and 24 h in co-culture when 33% of cell population was irradiated. In addition, survival reduction of bystander cells was increased with dose and saturated at 0.5 Gy. The dose responses were similar between carbon ions and -rays, indicating that bystander effects were partly dependent on dose but independent of radiation quality. Next, 0.001% of cell population was irradiated with carbon ion and neon ion (380 keV/m) microbeams. Bystander cells decreased their survival at 24 h but not at 6 h in co-culture. From these, it was estimated that bystander effects were also dependent on the fraction of irradiated cells.