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Change in oxygen enhancement ratio with depth in tissue-equivalent material for a collimated beam of fast neutrons

M.R.C. Radiobiology Unit, Harwell, Didcot, Oxon, and M.R.C. Cyclotron Unit, Hammersmith Hospital, London

Survival of reproductive capacity of murine leukaemia P-388 cells was assayed in vivo after the cells had been irradiated in vitro under aerobic or hypoxic conditions with collimated beams of X rays or 16 MeV D-Be fast neutrons at various depths in tissue-equivalent phantom material. The response to X-irradiation was the same in the absence of the phantom and at 8·7 cm depth. The response to fast neutrons under aerobic conditions was unchanged from 0 to 23 cm depth within the phantom. However, under hypoxic conditions, the dose-response curve for fast neutrons became significantly steeper with increasing depth in the phantom. The OER decreased from 2·0 in the absence of the phantom to 1·5 at 15 cm deep.

Received for publication July 1, 1975.