Chapter Eighteen - Proton linear accelerator and lithium target system

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Boron neutron capture therapy (BNCT) is a type of particle cancer therapy that uses alpha particles generated by a nuclear reaction between boron-10 and thermal neutrons and that destroys only cancer cells. Although this promising cancer treatment was previously possible only under the specialized conditions of a nuclear reactor, its spread to general medical institutions is becoming a reality as accelerators replace the research reactors as neutron sources. As a result, accelerator-based BNCT systems have been developed. The Cancer Intelligence Care Systems (CICS) BNCT system consists of an accelerator and a lithium target system. Particle accelerators with different characteristics are used for specific fields, and CICS uses a four-vane radio frequency quadrupole (RFQ) linear accelerator (linac) to enable low-energy, high-current proton acceleration of 2.5MeV and 20mA (CW), which is required for BNCT. Lithium and beryllium are currently the main target substances used for BNCT systems; lithium targets require lower energy (2.5MeV) than beryllium targets. Because the needed accelerator structure length is basically proportional to its beam energy, the lithium target system becomes compact. In addition, the radioactivity is slight because of its lower particle energy. CICS has installed an accelerator-based BNCT system, CICS-1, at the National Cancer Center (Tokyo) and is conducting clinical trials of BNCT for skin cancer.