Non-reactor neutron sources for BNCT [Boron Neutron Capture Therapy]

The focus of this study is the indentification of key feasibility issues for the use of non-reactor neutron sources for Boron Neutron Capture Therapy (BNCT). Of the non-reactor neutron sources surveyed, the 7Li(p,n) reaction appears to be the most favorable for producing epithermal neutrons for BNCT, and RFQ accelerators are best for producing the desired proton beam. At a proton energy of 2.5 MeV, the total neutron yield is 1.49 x 10-4 neutrons/proton, with a forward energy spectrum extending up to 780 keV and peaked at 500-600 keV. At I = 20 mA, the total neutron yield would be about 1.86 x 1013 neutrons/s. In comparison with a medical therapy fission reactor, the 20 mA accelerator system has a flux intensity at least 5 times lower, requiring an irradiation time at least 5 times longer, a much higher gamma intensity, which would probably require additional shielding, further reducing the neutron intensity, 30% of the neutrons above 15 keV, resulting in a higher fast neutron dose to healthy tissue, poorer spatial uniformity of the neutron beam, and greater angular divergence of the neutron beam, resulting in a rapid decrease of flux with distance from the filter. The possibility of overcoming these limitations by using more shielding and a higher beam current needs further study. RFQ accelerator technology is being developed to provide the desired proton beam parameters. The effects of neutron beam energy spectra, beam contaminants, angular divergence, spatial variation, and beam rotation around the tumor need to be studied in detail, in order to evaluate the feasibility of accelerator-produced neutrons for BNCT. 41 refs., 20 figs., 8 tabs