Biological intercomparison of d(50)-Be and p(75)-Be neutrons

A neutron beam with dose rate sufficiently high to be used for radiotherapy can be obtained by bombarding a thick beryllium target with 75 MeV protons. The radiobiological properties of p(75)-Be neutrons were studied with a view to clinical application. An intercomparison was made of the oxygen enhancement ratio (OER) and biological effectiveness of p(75)-Be and d(50)-Be neutrons using a variable energy cyclotron to irradiate Chinese hamster cells, with and without oxygen, at different depths in a tissue equivalent phantom. It is concluded from the resulting survival curves that p(75)-Be neutrons which exhibit advantages concerning depth-dose distribution are probably as interesting as d(16)-Be and d(50)-Be neutrons from the standpoint of OER, and that p(75)-Be neutrons are, on average, half as effective as d(16)-Be neutrons. (author)