Fast neutron beams for boron neutron capture therapy?

In view of Boron Neutron Capture Enhanced Fast Neutron Therapy (BNCEFNT) of brain tumours, the spatial distributions of thermal flux and fast neutron plus photon dose were measured in a hydrogenous cylinder phantom under conditions varying with respect to neutron energy, field size, and irradiation technique. The behaviour of the ratio thermal fluence per unit total dose leads to the conclusion that an appreciable dose contribution from the BNC reaction can be expected only with low energies and large fields. Beams from small apertures (< 6 x 6 cm2) produce only marginal BNC dose contributions, and might gain therapeutic relevance only in combination with a very effective tumour-seeking Boron-10 carrier.