An exploratory study of shielding strategies for boron neutron capture discrimination in 10B Neutron Capture Enhanced Particle Therapy

Abstract

Purpose: To evaluate the impact of a range of shielding strategies on the rate of false positive detections by a simulated detector for application in Neutron Capture Enhanced Particle Therapy (NCEPT).

Methods: In this work, we extend a previously published method for neutron capture detection and discrimination. A Geant4 Monte Carlo model was designed, with the simulated irradiation of a poly(methyl methacrylate) phantom and cubic ¹⁰B insert with carbon and helium ion beams and various shielding configurations.

Results: In the free-space configuration, shielding the crystal actually decreases the ratio of true/false positive detections (R_TF) by more than 50% and increases the activation of the detector. In a closed-space configuration with a model of the beamline neutron fluence, R_TF also decreases with shielding, although activation decreases in this case. However, for a detector with boron present in the printed circuit boards (PCBs), shielding with a thin layer of Gd₂O₃ improves R_TF by up to 21%.

Conclusions: Shielding of the detector crystal itself is unnecessary as shielding actually degrades discrimination accuracy relative to the unshielded detector. However, if the detector PCBs contain boron, then shielding the electronics provides a valuable increase in overall detector selectivity.

Keywords: Geant4; Monte Carlo; Neutron capture; Neutron shielding; Prompt gamma.