Accelerator neutron sources for BNCT: Current status and some pointers for future development.

Recent decades have seen the development of accelerator neutron sources suitable for installation in a hospital setting. Numerous challenges have been faced and solved to deliver technology which continues to transform the field of BNCT. This paper begins by briefly reviewing the technologies which are currently, or soon will be, in clinical use. This is followed by discussion of the thermal neutron fluence distributions produced by these accelerator sources and their associated beam shaping assemblies. This is illustrated by basic physics simulations of monoenergetic neutron fields, followed by some broad comparisons of the published distributions of thermal fluence produced by the different available technologies. It will be argued that these distributions have a high degree of similarity and that this similarity that can be helpful as the field of BNCT matures. Finally some aspects of the design of beam shaping assemblies and beam collimation will be discussed, and how this may enhance the capability of BNCT for verification of the delivered dose via the measurement of the prompt gammas emitted by the B (n, alpha) Li reaction. In particular the directionality of the beam will be discussed and measures that those designing beam shaping assemblies might consider to increase/improve beam directionality.