Evaluation of Moderator Assemblies for Use in an Accelerator-Based Neutron Source for Boron Neutron Capture Therapy

The neutron fields produced by several moderator assemblies were evaluated using both in-phantom and in-air neutron field assessment parameters. The parameters were used to determine the best moderator assembly, from among those evaluated, for use in our accelerator-based neutron source for boron neutron capture therapy. For a 10-mA proton beam current and the specified treatment parameters, a moderator assembly consisting of a BeO moderator and a Li₂CO₃ reflector was found to be the best moderator assembly whether the comparison was based on in-phantom or in-air neutron field assessment parameters. However, the parameters were discordant regarding the moderator thickness. The in-phantom neutron field assessment parameters predict 20 cm of BeO as the best moderator thickness, whereas the in-air neutron field assessment parameters predict 25 cm of BeO as the best moderator thickness.