A Monte Carlo dosimetry-based evaluation of the Li-7(p, n)Be-7 reaction near threshold for accelerator boron neutron capture therapy

Advanced methods of baron neutron capture therapy (BNCT) use an epithermal neutron beam in conjunction with tumor-targeting boron compounds for irradi ation of glioblastomas and metastatic melanomas. A common neutron-producing reaction considered for accelerator-based BNCT is Li-7(p,n)Be-7, whose cro ss section increases very rapidly within several tens of keV of the reactio n threshold at 1.88 MeV. Operation in the proton energy region near thresho ld will have an appreciable thick target neutron yield, but the neutrons pr oduced will have relatively low energies that require little moderation to reach the epithermal range desirable for BNCT. Because of its relatively lo w projected accelerator cost and the portability of the neutron source/targ et assembly, BNCT based on the near-threshold technique is considered an at tractive candidate for widespread hospital use. A systematic Monte Carlo N- Particle (MCNP) investigation of the dosimetric properties of near-threshol d neutron beams has been performed. Results of these studies indicate that accelerator proton energies between 1.93 and 1.99 MeV, using 5 cm of H2O mo derator followed by thin Li-6 and Pb shields, can provide therapeutically u seful beams with treatment times less than one hour and accelerator current s less than 5 mA. (C) 2000 American Association of Physicists in Medicine. [S0094-2405(00)03101-1].