Mutation induction in mammalian cells by accelerated heavy ions

The deleterious effects of accelerated heavy ions on living cells are of increasing importance for long duration human space flight activities. An important aspect of this field is attributed to the type and quality of biological damage induced by these densely ionizing particles. To address this aspect, cell inactivation and mutation induction at the HPRT locus (coding for hypoxanthine guanine phosphoribosyltransferase) was investigated in cultured V79 Chinese Hamster Cells irradiated with accelerated heavy ions (16-O, 40-Ca, 197-Au, and 238-U) and X-rays. Specific energies of the ions ranged from 1.9 to 69.7 MeV/u and corresponding LET values were between 62 and 15,580 keV μm ^-1. While inactivation cross-sections ( σ_i) rise over the whole LET range, mutation induction cross-sections ( σ_m) increase up to approximately 300 keV μm ^-1 (O-ions) but decline with heavier ions and more extreme LET values. A similar behavior is seen with mutation frequency dependent on particle fluence. After irradiation with accelerated uranium ions (8.8 MeV/u, 15,580 keV μm ^-1) a significant decrease of mutation frequency was found with higher particle fluences (3 × 10 ⁶ particles cm ^-2). Nearly no mutants were recovered with 8 × 10 ⁶ particles cm ^-2.