Microdosimetric quantities of an accelerator-based neutron source used for boron neutron capture therapy measured using a gas-filled proportional counter

• Published in: Journal of radiation research 2020-03, Vol.61 (2), p.214-220
• Main Authors: Hu, Naonori, Tanaka, Hiroki, Takata, Takushi, Okazaki, Keita, Uchida, Ryohei, Sakurai, Yoshinori
• Format: Article
• Language: English
• Subjects: Absorption, Radiation; Boron Neutron Capture Therapy - instrumentation; Computer Simulation; Gamma Rays; Gases - chemistry; Humans; Monte Carlo Method; Neutrons; Particle Accelerators; Radiotherapy Dosage; Regular Paper; Relative Biological Effectiveness
• ISSN: 0449-3060; 1349-9157
• DOI: 10.1093/jrr/rrz101

Abstract Boron neutron capture therapy (BNCT) is an emerging radiation treatment modality, exhibiting the potential to selectively destroy cancer cells. Currently, BNCT is conducted using a nuclear reactor. However, the future trend is to move toward an accelerator-based system for use in hospital environments. A typical BNCT radiation field has several different types of radiation. The beam quality should be quantified to accurately determine the dose to be delivered to the target. This study utilized a tissue equivalent proportional counter (TEPC) to measure microdosimetric and macrodosimetric quantities of an accelerator-based neutron source. The micro- and macro-dosimetric quantities measured with the TEPC were compared with those obtained via the the particle and heavy ion transport code system (PHITS) Monte Carlo simulation. The absorbed dose from events >20 keV/μm measured free in air for a 1-h irradiation was calculated as 1.31 ± 0.02 Gy. The simulated result was 1.41 ± 0.07 Gy. The measured and calculated values exhibit good agreement. The relative biological effectiveness (RBE) that was evaluated from the measured microdosimetric spectrum was calculated as 3.7 ± 0.02, similar to the simulated value of 3.8 ± 0.1. These results showed the PHITS Monte Carlo simulation can simulate both micro- and macro-dosimetric quantities accurately. The RBE was calculated using a single-response function, and the results were compared with those of several other institutes that used a similar method. However, care must be taken when using such a single-response function for clinical application, as it is only valid for low doses. For clinical dose ranges (i.e., high doses), multievent distribution inside the target needs to be considered.