The oxygen enhancement ratio for high energy neutrons.

Abstract

Neutron therapy is actively underway at a number of centres in Great Britain, the United States, continental Europe and Japan, using a wide range of neutron energies. Most clinical facilities utilize the d+→Be or p+→Be reactions, with the energy of the accelerated particle ranging from 16 MeV at Hammersmith to 67 MeV at the Fermilab. Over this range of neutron energies, the oxygen enhancement ratio (OER) appears to be relatively constant at 1.5 to 1.6, with the possibility of a small gradual increase in OER with neutron energy (Hall and Kellerer, 1979; Hall et al., 1977a). The reduced oxygen effect is the principal rationale for the introduction of neutrons into clinical practice as an alternative to X or γ rays, so the value of the OER is of basic importance. There have been reports in the literature that neutron energies higher than those currently in use may result in a lower OER; reports of experiments at the University of Maryland cyclotron indicated OER values of 1.3 and 1.2 for neutrons generated by 80 MeV deuterons and 101 MeV protons on beryllium respectively (Harrison et al., 1975; 1976). This possibility is obviously of great interest and importance from the point of view of choosing the energy range for future clinical facilities since a higher neutron energy would provide the additional benefits of improved depth doses and a higher dose-rate.