[Investigation of the processes of post-radiation reparation of the corneal epithelium cells of mice irradiated by helium ions with various LET values].

Biological effectiveness and post-radiation recovery of corneal epithelium cells of mice were studied. Mice were exposed to a broad range of doses from accelerated helium ions with the energy of 4 MeV/nucleon and 4 GeV/nucleon once and twice with a 24-hr. interval. LET values for these energies were 120 and 0.88 keV/microm, respectively. Gamma-source 137Cs (LET = 0.3 keV/microm) was used as a radiation standard. Animals irradiated by 25-400 sGy were sacrificed in 24 and 72 hrs. by way of cervical dislocation. Total corneal preparations made from enucleated eyeballs were analyzed for the mitotic index and aberrant mitoses using the anaphase method. High damaging properties of accelerated helium ions with the energy of 4 MeV/nucleon were manifested by a considerable reduction of the mitotic index and a more marked rise in the number of aberrant mitoses following the single and repeated exposure. Fractional irradiation by helium ions with the energy of 4 MeV/nucleon resulted in inhibition and even arrest of reparation suggesting additivity of separate radiation fractions. From the dose values that produced the double reduction of the mitotic index, coefficients of the relative biological effectiveness (RBE) for helium ions with the energy of 4 MeV/nucleon and 4 GeV/nucleon were estimated to be 5.3-8.6 and 1.3-1.8, respectively. In the context of the number of aberrant mitoses, RBE coefficients were significantly lower ranging 2.3-3.5 and 1.1-1.3 for these energies, respectively.