A calculational study of tangential and radial beams in HIFAR for neutron capture therapy.

It is generally accepted that for biological purposes a tangential neutron beam is preferable to a radial beam because of its lower gamma and fast neutron contamination. Nevertheless radial broad spectrum epithermal neutron beams are currently being considered for boron neutron capture therapy of deep-seated tumours since they have the potential to deliver a more intense dose. A calculational study of a conceptual tangential beam and a filtered radial beam in the DIDO type reactor HIFAR was undertaken. A two-dimensional transport code was used. The tangential beam was found to be superior in therapeutic gain at depth in tissue to an aluminium fluoride (AIF3) filtered radial beam, while the dose rates of the beams were comparable.