Calculated DNA double-strand break and fragmentation yields after irradiation with He ions

Tracks of He ions with LET values ranging from 7.6 up to 210 keV/μm were calculated by PARTRAC and radiation damage to DNA induced in human fibroblast cells was analysed using a higher-order DNA target model. Taking into account the resolution of experimental measurements of DNA fragmentation, the computed yields of DSBs relate to the experimentally observed LET dependence. Whereas the yields of total DSBs and of short DNA fragments continue to rise with increasing LET, the yields of intermediate DNA fragments (about 1-1000 kbp) have a maximum around an LET value of 100 keV/μm. A similar LET dependence in measured data for cell inactivation supports the hypothesis that multiple DSBs leading to fragments in this size region have an important role for this end point.