A pilot study of an epithermal neutron source based on a low-energy proton accelerator for boron neutron-capture therapy

In this study, a hospital-based low-energy proton accelerator neutron irradiation facility (LPANIF) for boron neutron capture therapy (BNCT) is described. Neutrons are generated by 2.5 MeV protons impinging upon a lithium-7 target. The neutrons emitted from the lithium target are too energetic for BNCT, and must be moderated. A moderator assembly served this purpose. The neutron field generated by the proposed facility has been studied both by calculations and by experiments. Calculations were performed for an experimental target and D2O moderator assembly using the Monte Carlo neutron transport code MORSE. The target and D2O moderator assembly were then constructed and tested in an experiment. The experiment was performed using the Ohio State University Van de Graaff accelerator to produce 2.5 MeV protons. New procedures were established to measure the neutron spectrum using a spherical proton recoil proportional counter. Also, a new instrument called boron-shell spectrometer was developed for measuring the neutron spectrum. In addition, the absorbed doses due to gamma-rays and 10B(n, α)7 Li reactions were also measured in a phantom which was exposed in the experimental neutron field. The calculated results agree reasonably well with the measured results. Having verified the author's calculational techniques for a non-optimum, but easily constructed, D2O moderator assembly an optimum moderator assembly was designed on the basis of Monte Carlo code results. The optimum moderator assembly is basically a beryllia (BeO) cylinder (25 cm in diameter and 22.5 cm in height) surrounded by a 30 cm thick alumina (Al2O3) reflector