Mutation Induction by Heavy Ion Beams and X-rays: Analysis with cultured cell line

This study was performed to determine the biological effects of heavy ion beams on cultured cells. V79 cells were irradiated with carbon or neon beams or X-rays, and cell survivals was calculated by the colony assay method. The Do values for 150 kVp X-rays, 20 keV/micron and 80 keV/micron carbon beams, and 80 keV/micron neon beams were 2.2Gy, 1.8Gy, 1.0Gy and 1.4Gy, respectively. After 7-10 day expression periods, the mutation frequencies at the hypoxanthine-guanine phosphribosyl transferase (hprt) locus were analyzed from the numbers of colonies formed in media supplemented with 6-thioguanine. An extremely higher frequency of mutation was observed with heavy ion beams compared with X-rays. Both cell killing effect and the mutation induction were enhanced when the LET of carbon beams was increased from 20 to 80 keV/micron. These results mean that carbon beams had a stronger cell-killing effect than X-rays, but also carried a high risk of mutation induction. On the other hand, neon beams yielded cell survival curves similar to those of carbon beams, but they had a smaller mutation induction effect than carbon beams. The effect of fractionated irradiation (3 hr interval) on cell survival and mutation frequency were also examined. When cells were irradiated with X-rays, cell survival was increased by fractionation, but the mutation frequency was not modified. Irradiating cells with fractionated carbon beams, survival curves were not affected, but mutation frequency was reduced.