RBE of nearly monoenergetic neutrons at energies of 36 keV-14.6 MeV for induction of dicentrics in human lymphocytes

We examined the induction of dicentric chromosomes in human lymphocytes irradiated in vitro with nearly monoenergetic neutrons at energies in the range of 36 keV–15.0 MeV. For the assessment of the relative biological effectiveness (RBE) both 220 kV x-rays and ⁶⁰Co -rays were used as reference radiations. To avoid potential confounding factors that would influence the outcome of the experiments, only blood from one individual was used. The neutron RBE culture conditions ensured that the chromosome analysis could be performed exclusively in metaphases of the first cell cycle in vitro. For the reference radiation of 220 kV x-rays, the values of RBE_M were found to increase from 16.6 (E_n=36 keV) to the maximum value of 23.4 (E_n=385 keV). For ⁶⁰Co -rays utilized as the reference radiation, the corresponding RBE_M values were found to be higher by a factor of 4. These results agree well with the previously published large data sets of three laboratories on dose-response relationships for dicentrics or dicentrics plus centric rings. They show a similar dependence of RBE on neutron energy.