Investigation on the efficacy of a tissue equivalent material bolus for BNCT

Background

In radiation therapy, the use of bolus is an effective technique for improving the surface dose. This irradiation technique is also used in BNCT. However, since BNCT uses neutron irradiation, it is important to evaluate both the neutron moderation characteristic and the radioactivation of the bolus.

Purpose

This study aimed to evaluate the tissue equivalence and activation of commercially available boluses for use in BNCT.

Methods

Two types of commercially available boluses were evaluated. The boluses were placed on a water phantom and irradiated using the NeuCure BNCT system. Firstly, the tissue equivalency of the boluses was evaluated by comparing the experimentally measured thermal neutron flux and gamma-ray distribution within the phantom, and the results were compared with simulation results. Secondly, the neutron activation of the boluses was assessed using an ionization chamber survey meter and an HP-Ge semiconductor detector to identify the produced radionuclides.

Results

The thermal neutron flux and gamma ray distribution in the water phantom agreed well between the measured and simulated results. The study revealed that both boluses became radioactive after neutron irradiation, primarily due to the production of radionuclides such as ²⁴Na and ³⁸Cl.

Conclusions

While boluses are effective in improving surface dose in BNCT, their use also introduces the risk of patient exposure to radiation from radioactivated bolus materials. Therefore, careful selection of bolus materials with minimal radioactivation is crucial to ensure patient safety.