Physical engineering for boron neutron capture therapy in KUR

Basic results of physical engineering study for neutron capture therapy in KUR have been reported since 1970, such as (1) development of thermal neutron fields for therapy following with low γ-ray, (2) development of thermal neutron shield material (6LiF) following with low secondary γ-ray, (3) establishment of measurement techniques for B-10 concentration in tissue by using then (n,γ) reaction, (4) evaluation of absorbed dose in a cell level during neutron capture therapy. It is difficult for many of thermal neutrons to reach to the depths in tissue. The thermal neutron irradiation, therefore, is suitable for the therapy of cancer on surface tissue, but not suitable for the therapy of cancer in the depths. Uses of epi-thermal (0.5 eV - 10 keV) or hyper-thermal (>0.5 eV) neutrons, instead of thermal neutron are considered for the neutron capture therapy to cancer in the depth. The depth dose distributions of thermal neutron are improved by increase of forward component of the epi-thermal or the hyper-thermal neutron. Thermal neutron fluxes have been measured by the activation method of Au-197. Thermo-luminescent detector (MgSiO4, or BeO) is used for the measurement of γ-ray doses. Noninvasive dose estimation at cancer parts is developed with a prompt γ-ray analysis method using HPGe and CdTe semiconductor detectors. (Suetake, M.)