Development of real-time thermal neutron monitor array for boron neutron capture therapy

Background: We have performed over 500 boron neutron capture therapy (BNCT) clinical studies using a research reactor. Irradiation time is evaluated by the measured neutron flux using gold activation methods at the surface of the affected area. To perform highly accurate BNCT treatment, it is desired to measure thermal neutrons in real time. Methods: We have developed a real-time thermal neutron detector array using a small scintillator combined with a quartz fiber to fulfill the required characteristics, including count rate, neutron field disturbance, radiation resistance, and gamma ray discrimination. A characteristic test was performed using reactor- and accelerator-based neutron sources. Results: We present the result of the performance test. One scintillator combined with a quartz fiber can measure the trends of thermal neutron flux up to 109 (n/cm2/s) using an accelerator-based neutron source. The newly developed detector array can also measure the one-dimensional thermal neutron flux up to 109 n/cm2/s. Furthermore, it is confirmed that a two-dimensional thermal neutron distribution can be measured by scanning with our developed detector array. Conclusions: A real-time neutron detector array was developed. According to the irradiation test using accelerator- and reactor-based neutron sources, it was confirmed that the developed system fulfilled the required characteristics.