Cell-killing effect of light- to heavy-ions in normal human fibroblasts

Yokota, Yuichiro; Funayama, Tomoo; Hamada, Nobuyuki*; Sakashita, Tetsuya; Kobayashi, Yasuhiko

High-LET heavy ions have a greater biological effect than low-LET photon radiation in normal tissues and tumors. In this study, we investigated the cell-killing effect of light- to heavy-ions in normal human fibroblasts to elucidate the mechanism underlying the great effects of heavy ions. Normal human diploid fibroblasts were kept as a confluent cell monolayer and irradiated with -rays (LET=0.2 keV/m), proton (2.8 keV/m), helium (17 keV/m), carbon (70 and 110 keV/m), neon (310 and 430 keV/m) and argon ions (1320 and 1530 keV/m). D values of -rays, proton, helium, carbon, neon and argon ions were 4.3 Gy, 3.2 Gy, 2.4 Gy, 1.0 Gy, 1.4-1.6 Gy and 3.7-5.0 Gy, respectively. RBE based on the D values arrived at the maximum of 4.3 at 70 and 110 keV/m, indicating that the cell-killing effect of carbon ions per dose was fourfold greater than that of -rays.