Boron Neutron Capture Therapy

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Research into BNCT became active again during the second half of the 1980s, especially basic research target-ing malignant glioma, particularly glioblastoma. Epithermal neutrons lose their energy by degrees as they react with various atoms in the body and change into thermal neutrons. The depth distribution of thermal neutrons gener-ated inside the body reaches its maximum value at a depth of 2 to 3 cm, about 3 times the value at the surface.Furthermore, the attenuation of generated thermal neutrons in tissue is relatively gradual. Consequently, by using an epithermal neutron beam, no craniotomy is needed for neutron irradiation at the research reactor site when BNCT is applied to malignant brain tumors. In the autumn of 1994, BNCT was performed without a cranioto-my at BNL’s research reactor in the U.S. using an epither-mal neutron beam. In Japan, KUR’s attached heavy-water thermal neutron facility was modified so that it could also use epithermal neutrons from 1995 to 1996. However, the fixation on use of a thermal neutron beam was strong among researchers who studied BNCT, and large-scale use of epithermal neutron beams had to wait for the arrival of this century. In Japan, the modifications at KUR were followed by similar changes at facilities operated by the former Japan Atomic Energy Research Institute.Since BNCT can be expected to yield clear effects with good accumulation of a boron compound, efficient treat-ment could be attained if such cancer patients could be selected by prior inspection.Fortunately, BPA can be labeled using 18F, a positron-emit-ting radionuclide, and its accumulation in tumors confirmed In addition to insufficient selective accumulation of boron compounds in tumors, the poor clinical results in the U.S. can be attributed to the low quality of the neutron beam that was used, that is, the mixing of an excessive level of gamma rays with a neutron beam. In Japan, an improved neutron beam port was used in clinical research. In particular, a heavy by means of PET. Furthermore, the accumulation ratio in actual BNCT can be predicted by the ratio of 18F radioactivi-ty in the tumor and that in normal tissue (blood). The world’s first BNCT procedure based on this prior inspection using FBPA PET was performed using KUR in February 1994, and it yielded the expected results.Epithermal neutronImproved thermal neutron beam facilityFrom using thermal neutrons to using epithermal neutrons (described in detail elsewhere in this pamphlet)Appearance of FBPA PET (described in detail elsewhere in this pamphlet)ment in Japan lead BNCT research in the world.water facility capable of extracting thermal neutrons at a high level of purity was added to KUR. While this facility was not specialized for BNCT, it provided a high level of thermal neutron purity with a Cd ratio of 5,000 and a thermal neutron fluence rate of 6×109 n/cm2•s. A facility of the highest caliber, it was used in 1974 for the first BNCT at KUR.0.0015100.010.1110Thermal neutron depth distribution(during irradiation with an epithermal neutron beam)Thermal neutron depth distribution(during irradiation with a thermal neutron beam)Depth (cm)Thermal neutron uence rate(relative value)4

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