Evaluation of radioactivity in the bodies of mice induced by neutron exposure from an epi-thermal neutron source of an accelerator-based boron neutron capture therapy system

Abstract

This study aimed to evaluate the residual radioactivity in mice induced by neutron irradiation with an accelerator-based boron neutron capture therapy (BNCT) system using a solid Li target. The radionuclides and their activities were evaluated using a high-purity germanium (HP-Ge) detector. The saturated radioactivity of the irradiated mouse was estimated to assess the radiation protection needs for using the accelerator-based BNCT system. 24Na, 38Cl, 80mBr, 82Br, 56Mn, and 42K were identified, and their saturated radioactivities were (1.4 ± 0.1) × 102, (2.2 ± 0.1) × 101, (3.4 ± 0.4) × 102, 2.8 ± 0.1, 8.0 ± 0.1, and (3.8 ± 0.1) × 101 Bq/g/mA, respectively. The 24Na activation rate at a given neutron fluence was found to be consistent with the value reported from nuclear-reactor-based BNCT experiments. The induced activity of each nuclide can be estimated by entering the saturated activity of each nuclide, sample mass, irradiation time, and proton current into the derived activation equation in our accelerator-based BNCT system.

Characterization of the relationship between neutron production and thermal load on a target material in an accelerator-based boron neutron capture therapy system employing a solid-state Li target

“…Based on the results of in vivo and in vitro experiments, boron neutron capture therapy (BNCT) is expected to kill cancer cells that are resistant to conventional radiotherapies, such as photon therapy [1–5]. This is because compounds containing 10 B are delivered to the cancer cells, which are then killed by the 10 B(n, α) 7 Li reaction caused by neutron irradiation [2, 6].…”

Neutron flux evaluation model provided in the accelerator-based boron neutron capture therapy system employing a solid-state lithium target

“…Recent studies have indicated that accelerator-based neutron sources can achieve sufficient neutron flux for use in BNCT 20 – 24 . Two main types of accelerator-based neutron sources are generally considered to acquire neutrons for accelerator-based BNCT systems.…”

“…To generate the neutrons, one source utilizes the reaction of 7 Li(p, n) 7 Be, whereas the other source utilizes the reaction of 9 Be(p, n) 9 B 20 – 26 . In the former system, the maximum generated neutron energy is below 1 meV and the incident proton energy of around 2.5 meV is generally considered, whereas that for the latter system is higher by a few MeV (i.e., the incident proton energy is higher than 8 meV) 20 – 24 . Therefore, the advantage of the former system is that the lower neutron energy facilitates a more compact BNCT system as the generated neutrons can be easily moderated to produce the ideal neutron energy (approximately 10 keV).…”

“…However, a disadvantage is that the melting point of Li is lower than that of Be as a high thermal loading is required on the Li target 20 , 27 , 28 . Considering these properties, the National Cancer Center Hospital (NCCH), Tokyo, Japan, is conducting a clinical study using an accelerator-based BNCT system employing the Li target to evaluate its efficacy in clinical oncology 20 , 23 , 24 .…”

Water-Soluble closo-Docecaborate-Containing Pteroyl Derivatives Targeting Folate Receptor-Positive Tumors for Boron Neutron Capture Therapy

“…Therefore, the combination of boron agents with sufficient and selective accumulation of 10 B in cancer cells and an appropriate neutron source is essential for successful cancer treatment with BNCT [1,2]. In the last decade, accelerator-based thermal neutron generators for BNCT have been developed worldwide [3][4][5][6][7][8][9][10], and one was approved in Japan this year as a medical device [6,7] in combination with L-4-boronophenylalanine (L-BPA) [11] for the treatment of head and neck carcinoma patients. It is known that L-BPA is actively accumulated into cancer cells through L-type amino acid transporter 1 (LAT-1) [12,13], which is overexpressed in many cancer cells.…”