The Response of Chinese Hamster Ovary Cells to Fast-Neutron Radiotherapy Beams: II. Sublethal and Potentially Lethal Damage Recovery Capabilities

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Abstract
The recovery capabilities of mammalian [Chinese hamster ovary CHO] cells in culture were investigated after irradiation with fast neutrons. Two different neutron beams (mean neutron energy 7 and 21 MeV) were used in these studies. The ability of fast-neutron-irradiated cells to recover from sublethal damage was tested in fractionated dose experiments. No recovery was detected after irradiation with total doses of fast neutrons up to 300 rad. After a total dose of 500 rad, a recovery factor of about 1.5 was observed, which was considerably less than that observed when the cells were irradiated with 60Co .gamma.-rays to a comparable survival level. The recovery capabilities of cells were not significantly different for the 2 neutron beams. The ability of fast-neutron-irradiated cells to recover from potentially lethal damage was tested by irradiating cells in the plateau phase of growth and plating the cells either immediately after the irradiation or 8 h later. No difference in survival was observed when neutron-irradiated plateau-phase cells were plated at these 2 times, whereas 60Co .gamma.-irradiated cells showed a factor of 2-3 increase in survival when plated 8 h after irradiation.