11:15 AM - 11:30 AM
[18a-A304-6] Development of irradiation field for cell and small animal using cyclotron-based neutron source
Keywords:boron neutron capture therapy, accelerator-based neutron source, Thermal neutron
Boron neutron capture therapy is a treatment to kill cancer cells using alpha particle and Li nucleus generated by the reaction between thermal neutron and boron-10. There are only two kinds of boron compounds currently in clinical use, and new boron compounds are being actively developed. In order to confirm the effect of the boron compound, it is necessary to confirm the cell killing effect on the cells and the antitumor effect on the tumor transplanted to the small animal by thermal neutron irradiation, which is almost equivalent to the neutron intensity as clinical use. At Kyoto University Research Reactor (KUR), heavy water irradiation field has been used, but it is necessary to suspend operation due to regular inspection for about 3 months per year. In further promoting the development of boron compounds, it is desired to continuously supply a thermal neutron irradiation field. Therefore, in this research, we are investigating a method to form thermal neutron irradiation field for cells and small animals using Cyclotron-based Neutron Source (CBNS).
CBNS consists of a cyclotron that can produce 30 MeV 1 mA proton beam, beam transport system, beryllium target and moderator. Since the moderator can generate only epithermal neutrons for clinical use, in order to irradiate thermal neutrons to cells and small animals, it is necessary to thermalize to thermal neutron energy range. As a method of thermalizing, a water phantom was installed at the irradiation port. Thermal neutron flux distribution in water phantom measured by gold activation method was derived. At the 20 mm peak position, it was confirmed that the thermal neutron flux was over 1 x 10 ^9 (n / cm ^2 / s). It is necessary to consider the dose rate of gamma ray, nitrogen (N), hydrogen (H), boron (B) per 1 ppm in the thermal neutron irradiation field. Each dose rate was evaluated. For the purpose of comparison, the dose rate of the irradiation field of KUR, which has been conventionally used, was shown. The dose rate of gamma rays was about 2.5 times higher than KUR. It was confirmed that other dose rates were almost equivalent. Although the dose rate of gamma rays is high, it seems that it has no influence on observing the effect because of its high biological effect and high concentration of boron in the tumor.
CBNS consists of a cyclotron that can produce 30 MeV 1 mA proton beam, beam transport system, beryllium target and moderator. Since the moderator can generate only epithermal neutrons for clinical use, in order to irradiate thermal neutrons to cells and small animals, it is necessary to thermalize to thermal neutron energy range. As a method of thermalizing, a water phantom was installed at the irradiation port. Thermal neutron flux distribution in water phantom measured by gold activation method was derived. At the 20 mm peak position, it was confirmed that the thermal neutron flux was over 1 x 10 ^9 (n / cm ^2 / s). It is necessary to consider the dose rate of gamma ray, nitrogen (N), hydrogen (H), boron (B) per 1 ppm in the thermal neutron irradiation field. Each dose rate was evaluated. For the purpose of comparison, the dose rate of the irradiation field of KUR, which has been conventionally used, was shown. The dose rate of gamma rays was about 2.5 times higher than KUR. It was confirmed that other dose rates were almost equivalent. Although the dose rate of gamma rays is high, it seems that it has no influence on observing the effect because of its high biological effect and high concentration of boron in the tumor.