Current Research on Accelerator-based Boron Neutron Capture Therapy in Korea

Boron Neutron Capture Therapy (BNCT) is a binary radiation treatment modality based on nuclear reactions between thermal neutrons and stable isotope B concentrated primarily in cancer cells. It allows for delivery of high linear energy transfer (LET) radiation ( particles and Li nuclei) to tumors at the cellular level whilst avoiding unnecessary dose deposition to healthy tissue. Until now, most BNCT studies and clinical treatments have been performed by using research reactors that have always produced various neutrons from a nuclear fission chain reaction [1-3]. However, these reactors are difficult to install into the hospitals and their use is burdened by licensing and spent nuclear fuel disposal issues [4]. To overcome some of the issues related to reactor-based neutron sources, research centered on accelerator-based BNCT as a useful alternative have surfaced in recent years. BNCT treatment using accelerator-based neutron sources is not without its own requirements, however: (i) appropriate neutron-producing target and cooling equipment are required; (ii) beam-shaping assemblies consisting of moderators, reflectors, and so on, that can provide a neutron energy spectrum suitable for patient irradiation, are required; and (iii) Treatment Planning System (TPS) for determining optimal configurations are required. Research have been performed for the design, manufacturing, and testing of the above-mentioned components at the Massachusetts Institute of Technology, Idaho National Engineering and Environmental Laboratory, Lawrence Berkley National Laboratory, University of Birmingham, Hanyang University, and so on [5-11]. In particular, Japan has made the ample funds to realize accelerator-based BNCT, and extent studies including clinical demonstrations have been progressed in recent years. Until now, most efforts for accelerator-based BNCT have been focused on the design and testing of beamshaping assemblies to investigate the feasibility of clinical neutron beams having the desired characteristics for patient irradiation. Target and cooling equipment, on the other hand, has not seen much attention. This paper is intended to provide key issues and current research outcomes on accelerator-based Boron Neutron Capture Therapy (BNCT). Accelerator-based neutron sources are efficient to provide epithermal neutron beams for BNCT; hence, much research, worldwide, has focused on the development of components crucial for its realization: neutron-producing targets and cooling equipment, beam-shaping assemblies, and treatment planning systems. Proton beams of 2.5 MeV incident on lithium target results in high yield of neutrons at relatively low energies. Cooling equipment based on submerged jet impingement and micro-channels provide for viable heat removal options. Insofar as beam-shaping assemblies are concerned, moderators containing fluorine or magnesium have the best performance in terms of neutron accumulation in the epithermal energy range during the slowing-down from the high energies. NCT_Plan and SERA systems, which are popular dose distribution analysis tools for BNCT, contain all the required features (i.e., image reconstruction, dose calculations, etc.). However, detailed studies of these systems remain to be done for accurate dose evaluation. Advanced research centered on accelerator-based BNCT is active in Korea as evidenced by the latest research at Hanyang University. There, a new target system and a beam-shaping assembly have been constructed. The performance of these components has been evaluated through comparisons of experimental measurements with simulations. In addition, a new patient-specific treatment planning system, BTPS, has been developed to calculate the deposited dose and radiation flux in human tissue. It is based on MCNPX, and it facilitates BNCT efficient planning based via a user-friendly Graphical User Interface (GUI).