Radiobiological studies with therapeutic neutron beams generated by p+→Be or d+→Be

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Abstract
Mammalian cells [Chinese hamster lung V-79 fibroblasts] cultured in vitro were used to study the radiobiological characteristics of neutron beams generated by 43 MeV protons on Be or 25 MeV deutrons on Be. For an unfiltered beam of neutrons generated by 43 MeV p+ .fwdarw. Be the relative biological effectiveness [RBE] was 8-12% higher at a depth of 2 cm than at a depth of 12 cm due to the presence of a large component of low-energy neutrons. The addition of a hydrogenous filter 4 cm thick preferentially removed the low-energy neutrons from the beam and, as a result, the neutron RBE was independent of depth. There was no significant difference in the oxygen enhancement ratio [OER] between the filtered neutrons produced by 43 MeV p+ .fwdarw. Be and neutrons produced by 25 MeV d+ .fwdarw. Be; for both beams the OER value was about 1.6.