Boron Neutron Capture Therapy

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Neutron sourceDeveloping a neutron source and controlling the complex mix of radiation doses that exist in the irradiation fieldIn its present form, BNCT is based on epithermal neutron irradiation. Currently, the only facilities used as sources of neutrons for BNCT in Japan are the Kyoto University Research Reactor (KUR) Heavy Water Neutron Irradiation Facility and the cyclotron accelerator system at the Kyoto University Research Reactor Institute, shown in Photo-graphs 1 and 2. Both nuclear reactors and accelerators have deceleration systems capable of converting the generated fast neutrons into epithermal neutrons. Figure 3 illustrates the energy distribution for the epithermal neutrons produced by these systems. The energy of epith-ermal neutrons is considered to range from 0.5 eV to 40 keV, taking into account the radiation weighting factor. To date, the KUR Joint-use Medical Treatment Group has verified the effectiveness of BNCT by offering the treatment to more than 500 patients using reactor neutrons and has also developed an accelerator neutron source for BNCT to facilitate wider use of the technique. In an effort to earn regulatory approval for the technique, the group began clinical trials on the treatment of recurrent glioma in Octo-ber of 2012 and are to commence clinical trials dealing with the treatment of locally recurrent head and neck cancers from spring 2014 by using this accelerator–moderator system.Figure 3. Epithermal Neutron Energy Distribution••••30 MeV, 1 mA protonsNumber of neutrons generated: Approximately 1015 per second(Target: Be; diameter: approximately 16 cm)Epithermal neutron flux used at radiation port: Approximately 1 × 109 s-1cm-2Average energy of generated neutrons: Approximately 10 MeVPhotograph 2. Accelerator Neutron Source••••5 MWNumber of nuclear fissions: Approximately 1017 per second(Reactor core: 60 cm3)Epithermal neutron flux used at radiation port: Approximately 5 × 108 s-1cm-2Average energy of generated neutrons: Approximately 1.5 MeVPhotograph 1. Reactor Neutron SourceA neutron source for BNCT00.20.40.60.81.010⁰10-⁸10-⁶10-⁴10-²Neutron energy (MeV)Neutron ux (relative value)Fromreactor neutron sourceFromaccelerator neutron sourceThe mode energy values for epithermal neutrons produced in the reactor and accelerator are approximately 1 eV and 10 keV, respectively.13

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