Spectrum Shaping of Epithermal Neutron Beam for Accelerator-Based BNCT and Dosimetric Evalution Using a Brain Phantom

Abstract

Accelerator-based 7Li(p,n)7Be reaction is a favorable way to get neutron source for Boron Neutron Capture Therapy (BNCT). It is widely recognized that epithermal neutrons are more effective than thermal ones in order to treat deep-seated brain tumors with BNCT. For treatment of a deep-seated brain tumor, in addition, it is desirable to use an epithermal neutron beam which has a narrow spectrum concentrated on a specific energy showing good dosimetric properties. With the aim of producing the epithermal neutron beam, various materials for spectrum shaping have been investigated and some dosimetric properties for the beam have been analyzed by using a brain phantom. The neutron source was assumed to be produced from a conventional 2.5 MeV proton accelerator with a thick Li-7 target. All elements with essentially high resonance scattering cross section have been analyzed to determine moderators suitable to spectrum shaping into the useful epithermal neutron beam. Additional uses of Al and, particularly, Ni-60 to the primary moderator, A1F3, were found to be very effective for producing epithermal neutron beams with narrow spectra. The results from dosimetric evaluation indicate that the epithermal neutron beams designed in this study can treat more effectively deep-seated brain tumor.