Micronuclei, CREST-positive micronuclei and cell inactivation induced in Chinese hamster cells by radiation with different quality

Purpose: To study the relative biological effectiveness-linear energy trans fer (RBE-LET) relationship for micronuclei (MN) and cell inactivation, in C hinese hamster cells irradiated with low-energy protons (0.88 and 5.04 MeV, at the cell entrance surface). Chromosome loss was also investigated by me ans of antikinetochore CREST staining. Materials and methods: Cl-1 cells were exposed to different doses of X-rays , gamma-rays, 7.7 keV/mu m and 27.6 keV/mu m protons. The induction of MN, the distribution of MN per cell and the frequency of CREST-positive MN were evaluated in cytokinesis-blocked binucleated cells (BN cells) in the dose range 0.125-3 Gy. In parallel, cell survival experiments were carried out i n samples irradiated with 0.5 to 4 Gy. Results: MN yield and the frequency of BN cells carrying multiple MN (great er than or equal to 2) were significantly higher after exposure to 27.6 keV /mu m protons, compared with the other radiation types. In contrast, MN ind uction and MN distribution per BN cell were similar among 7.7 keV/mu m prot ons, X- and gamma-rays up to 1 Gy. Cell survival experiments gave RBE value s very close to those obtained with the MN assay. Both X-rays and 27.5 keV/ mu m protons yielded a significant proportion of CREST-positive MN at the h ighest doses investigated (0.75-3 Gy). Conclusions: Good correlations between MN induction and cell inactivation w ere observed for both low- and high-LET radiation, indicating that the MN a ssay can be a useful tool to predict cell sensitivity to densely ionizing r adiation with implications for tumour therapy with protons.