Abstract
Purpose: To investigate the LET and ion species dependency for PLDR in normal human embryonic lung fibroblasts, cells were irradiated with high- or low-LET radiations, and the colony forming capacities were measured.
Materials and Methods: Normal human embryonic lung fibroblasts were irradiated with X-ray or heavy-ion beams, such as carbon- (290MeV/u or 135MeV/u), neon- (400MeV/u), silicon- (490MeV/u) or iron- (500MeV/u) ion beams, generated by Heavy Ion Medical Accelerator in Chiba (HIMAC). Cell-killing efficiencies were measured using a colony-formation assay as immediate plating (IP) method or delayed plating (DP) method after kept them at 370C for 24hours.
Results and Conclusion: The D10 values were calculated from survival curves of IP or DP irradiated with X-rays or heavy ions (LET:13keV/um~400keV/um). The RBE values of IP in heavy ions calculated by the D10 values were ranging from1.18 to 2.88 relative to X-rays, and that of DP were ranging from 1.28 to 4.11. The ratio of DPD10/IPD10 was ranging from 1.80 to 1.13. PLDR was decreased with increasing LET values and the RBE values of DP were higher than those of IP. The PLDR was different in different ion species, even if the LET values were similar. Those results showed that PLDR depended on both LET and ion species.
