V79 survival following simultaneous or sequential irradiation by 14.8-MeV neutrons and 60Co photons

A unique tandem source irradiation facility, comprised of an intense d-T neutron source and a 60Co teletherapy unit, has been used to investigate biological response for different neutron/photon configurations. V79 Chinese hamster cells, attached as monolayers in log phase growth, were irradiated at 370C by either 14.8 MeV neutrons, 60Co or by a mixture of 40% neutrons - 60% photons in simultaneous or sequential application. Measurements of cell survival indicate an increased effectiveness in cell killing for simultaneously administered neutrons and photons than was measured or predicted for sequentially applied beam modalities. An understanding of the magnitude of these interactive effects is important both for calculating accurate effective doses for neutron radiotherapy of deep-seated tumors, for which the photon component is appreciable and for determination of environmental hazards to people occupationally exposed to low levels of photons and neutrons