Neutronic design of a fission converter-based epithermal neutron beam for neutron capture therapy

To meet the needs for neutron capture therapy (NCT) irradiations, a high-in tensity, high-quality fission converter-based epithermal neutron beam has b een designed for the MITR-II research reactor. This epithermal neutron beam , capable of delivering treatments in a few minutes with negligible backgro und contamination from fast neutrons and photons, will be installed in the present thermal column and hohlraum of the 5-MW MITR-II research reactor. S pent or fresh MITR-II fuel elements will be used to fuel the converter. Wit h fission converter power of similar to 80 kW using spent fuel, epithermal fluxes (1 eV < E < 10 keV in excess of 10(10) n/cm(2).s are achievable at t he target position with negligible photon and fast neutron contamination, i .e., <2 x 10(-11) cGy.cm(2)/n. With the currently available B-10 delivery c ompound boronophenylalanine-fructose, average therapeutic ratios of similar to 5 can be achieved using this beam for brain irradiations with deep effe ctive penetration (similar to 9.5 cm) and high dose rates of up to 400 to 6 00 RBE cGy/min. If NCT becomes an accepted therapy, fission converter-based beams constructed at existing reactors could meet a large fraction of the projected requirements for intense, low-background epithermal neutron beams at a relatively low cost. The results of an extensive set of neutronic des ign studies investigating all components of the beam are presented. These d etailed studies can be useful as guidance for others who may wish to use th e fission converter approach to develop epithermal beams for NCT.