Change in radiosensitivity with fractionated-dose irradiation of carbon-ion beams in five different human cell lines

Purpose: To investigate the change in the surviving fractions by fractionat ed-dose irradiations with carbon ions, based on the recovery of potentially lethal damage (PLDR) and the change of radiosensitivity by every fractiona ted-dose irradiation. Methods and Materials: One normal human and four human-tumor cell lines wer e used. Cells were irradiated with carbon ions accelerated by the Heavy Ion Medical Accelerator in Chiba (HIMAC) at National Institute of Radiological Sciences in Japan. The LET values were estimated to be 13.18 keV/mu m for low-LET beams and 76.92 +/- 0.20 keV/mu m for high-LET beams. Fractionated- dose irradiations were carried out with 5 fractions within a 24-h interval. Results: The surviving fractions for the fractionated-dose irradiation with X-rays and carbon ions decreased exponentially with increasing the number of fractions in the tumor cell lines. In contrast, the surviving fractions for the carbon ions in normal human cells decreased exponentially as well a s the tumor cell lines, while it tended to level off from the 3rd to the 5t h fraction in the case of using X-rays. Conclusion: The change in both the recovery ratio of the PLDR and radiosens itivity by every fractionated-dose irradiation depends on individual cell l ines and the quality of radiations. (C) 2000 Elsevier Science Inc.