The repair of sublethal damage in cultured cells derived from a mouse squamous cell carcinoma following an irradiation of mixed neutrons and x-rays

The effect of combined high-and low-LET irradiations on the cultured murine squamous carcinoma Sq-1979 cells were studied. Neutrons were produced by NIRS cyclotron by bombarding 30 MeV neutrons on a beryllium target. An x-ray unit was operated at 200 kVp. The cells were irradiated with split-dose schedules to investigate the repair capability. Firstly, Elking-type recovery curves were obtained in 4 irradiation schedules, i.e., X-X, X-N, N-X, N-N. X-ray and neutron doses were 6 Gy and 4 Gy respectively. The most substantial repair was observed following two x-ray doses, although the mixed beam modalities inhibited the repair of sublethal damage as well as the two neutrons doses. Secondly, the cell survival curves were obtained following graded doses of x-rays or neurtons given of 0, 3, and 22 hrs after a priming dose of 6 Gy of x-rays or 4 Gy of neurtons. The mixed beam irradiations (X-N or N-X) given with a treatment interval of 3 hrs inhibited the repair of sublethal damage, indicating a synergistic effect of the mixed beam. At a treatment interval of 22 hours N-X and N-N groups demonstrated a slight synergistic effect, but, X-N group appeared to lost the synergism within 22 hours. These results indicate that the synergistic effect between low- and high-LET mixed beam might be related to the cellular capability of repairing sublethal damage. (author)