On the Eptihermal Neutron Energy Limit for Accelerator-Based Boron Neutron Capture Therapy (AB-BNCT): Study and Impact of New Energy Limits

TL;DR

This study uses Monte Carlo simulations to determine that lower epithermal neutron energies (10 eV to 1 keV) can enhance the effectiveness of accelerator-based boron neutron capture therapy for deep-seated tumors.

Contribution

It identifies optimal neutron energy ranges for AB-BNCT, suggesting that energies below 10 keV improve therapeutic gain for tumors at various depths.

Findings

Lower neutron energies increase therapeutic gain for tumors up to 6.4 cm deep.

Neutrons between 10 eV and 1 keV outperform 10 keV neutrons in treatment efficacy.

Using lower energies reduces healthy tissue dose, potentially improving treatment safety.

Abstract

Background and purpose: Accelerator-Based Boron Neutron Capture Therapy is a radiotherapy based on compact accelerator neutron sources requiring an epithermal neutron field for tumour irradiations. Neutrons of 10 keV are considered as the maximum optimised energy to treat deep-seated tumours. We investigated, by means of Monte Carlo simulations, the epithermal range from 10 eV to 10 keV in order to optimise the maximum epithermal neutron energy as a function of the tumour depth. Methods: A Snyder head phantom was simulated and mono-energetic neutrons with 4 different incident energies were used: 10 eV, 100 eV, 1 keV and 10 keV. $^{10}$B capture rates and absorbed dose composition on every tissue were calculated to describe and compare the effects of lowering the maximum epithermal energy. The Therapeutic Gain (TG) was estimated considering the whole brain volume. Results: For tumours seated at 4 cm depth, 10 eV, 100 eV and 1 keV neutrons provided respectively 54 $\%$, 36 $\%$ and 18 $\%$ increase on the TG compared to 10 keV neutrons. Neutrons with energies between 10 eV and 1 keV provided higher TG than 10 keV neutrons for tumours seated up to 6.4 cm depth inside the head. The size of the tumour does not change these results. Conclusions: Using lower epithermal energy neutrons for AB-BNCT tumour irradiation could improve treatment efficacy, delivering more therapeutic dose while reducing the dose in healthy tissues. This could lead to new Beam Shape Assembly designs in order to optimise the BNCT irradiation.