Effects of Neutron Collimation, Beam Size, and Spectrum on In-Phantom Performance of Realistic Epithermal Neutron Beams for BNCT

Abstract

Sensitivity studies of the collimator and fast neutron filter/moderator designs of the MIT fission converter epithermal neutron beam have been conducted to examine the effects of beam collimation or directionality, beam size (i.e., neutron spatial distribution), and neutron spectrum on dosimetric performance in a water-filled ellipsoidal head phantom. The effects of these beam parameters have already been studied using ideal beams, i.e., monoenergetic, photon-free neutron beams with varying maximum neutron emission angle and beam size.1 In those ideal beam studies, the effect of each parameter was examined separately by varying one parameter with the others fixed. However, in actual beam design, these three parameters, especially beam directionality and beam size, (and intensity as well), vary simultaneously, resulting in a much more complex optimization problem. The current study examines the effects of these beam characteristics using realistic epithermal neutron beams to evaluate their relative importance in treating brain tumors.