Comparison of biological efficiency of accelerated carbon ions and heavy recoils in Chinese hamster cells

The article presents results of study of relative biological efficiency (RBE) of accelerated carbon ions at а plateau and the peak of the Bragg curve, as well as RBEs of C, N, O heavy recoils induced by 14.1 MeV neutrons in the cell monolayer irradiated in the absence of secondary charged particles equilibrium (SCPE). Normal (V-79 and CHO-K1) and tumor (B14-150) Chinese hamster cells were irradiated by accelerated carbon ions from the U-70 accelerator (NRC «Kurchatov Institute» - IHEP, Protvino, Russia) and 14.1 MeV neutrons from the portable neutron generator NG-14 (Dukhov Research Institute of Automatics, Moscow, Russia). To assess biological efficiency of different radiations clonogrnic survival assay was used. For carbon ions the survival curves were exponential at the Bragg peak and sigmoid at the Bragg curve plateau, while the curves for neutrons in the SCPE absence were exponential. The RBE values at 10% survival did not differ for different cell lines, they amounted to 1.3-1.4. RBEs of carbon ions in the plateau and the Bragg peak were 4.1 and 4.2, respectively. RBE of heavy recoils (C, N, O) was 3.1. RBEs of the accelerated carbon ions and heavy recoils were consistent with the well-known LET-RBE relationship. The used method for exposure of cell monolayers to 14.1 MeV neutrons in the SCPE absence allows researchers to study radiobiological effects under conditions simulating the Bragg peak of accelerated 12C ions.