title: A fundamental study on hyper-thermal neutrons for neutron capture therapy.
abstract: The utilization of hyper-thermal neutrons, which have an energy spectrum with a Maxwellian distribution at a higher temperature than room temperature (300 K), was studied in order to improve the thermal neutron flux distribution at depth in a living body for neutron capture therapy. Simulation calculations were carried out using a Monte Carlo code 'MCNP-V3' in order to investigate the characteristics of hyper-thermal neutrons, i.e. (i) depth dependence of the neutron energy spectrum, and (ii) depth distribution of the reaction rate in a water phantom for materials with 1/v neutron absorption. It is confirmed that hyper-thermal neutron irradiation can improve the thermal neutron flux distribution in the deeper areas in a living body compared with thermal neutron irradiation. When hyper-thermal neutrons with a 3000 K Maxwellian distribution are incident on a body, the reaction rates of 1/v materials such as 14N, 10B etc are about twice that observed for incident thermal neutrons at 300 K, at a depth of 5 cm. The limit of the treatable depth for tumours having 30 ppm 10B is expected to be about 1.5 cm greater by utilizing hyper-thermal neutrons at 3000 K compared with the incidence of thermal neutrons at 300 K.
authors.affiliation: Research Reactor Institute, Kyoto University, Kumatori-cho, Sennan-gun, Osaka 590-04, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Sakurai
authors.forename: T
authors.initials: T
authors.lastname: Kobayashi
authors.forename: K
authors.initials: K
authors.lastname: Kanda
mesh_terms: D001921:Brain / Q000473:pathology; D005720:Gamma Rays; D006801:Humans; D008962:Models, Theoretical; D009010:Monte Carlo Method; D017247:Neutron Capture Therapy / Q000295:instrumentation* / Q000379:methods*; D009502:Neutrons; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D013696:Temperature