Intercomparison of personal and ambient neutron detectors used for radiation protection in a synchrotron-based proton therapy facility: experimental and Monte Carlo results

Purpose

This study evaluates ambient and personal neutron detectors in a synchrotron-based proton therapy facility, using experimental data and Monte Carlo (TOPAS) simulations. It aims to assess the interchangeability of detectors, characterize neutron doses in the treatment room, and provide radiological protection recommendations. Method: A 10 × 10 × 10 cm³ volume (energy range: 121–173 MeV) was irradiated on a 30 × 30 × 60 cm³ solid water phantom. Ambient dose equivalent (H*(10)) was measured using two extended-energy-range detectors (LUPIN-II, WENDI-II) at 20 positions. Personal dose equivalent (H_p(10)) was evaluated using five dosimeters (bubble detectors, DOPEN tracks, NeutrakT, MCP6/MCP7 TLDs, NRF51 EPD) at 14–20 positions. Bland-Altman analysis quantified agreement. TOPAS, a Monte Carlo code, was employed to calculate neutron spectra and to compare the results with experimental H*(10) values for its validation. Results: The WENDI-II and LUPIN-II detectors showed good agreement, with WENDI-II readings 14 % higher on average. Among personal dosimeters, DOPEN tracks exhibited the closest agreement with bubble detectors, with a bias of −33 %. In constrast, NeutrakT underperformed due to its high detection limit. TOPAS simulations aligned with experimental H*(10) trends, with differences ranging from 0 to 32 %, except for positions involving significant PMMA attenuation. Neutron spectra revealed angular and distance-dependent variations, with thermal neutrons dominating at larger distances. Conclusions: Both WENDI-II and LUPIN-II are suitable for environmental neutron monitoring in synchrotron-based facilities. DOPEN tracks emerged as the most reliable passive personal dosimeter for H_p(10). Monte Carlo simulations enhanced understanding of neutron field behavior and were validated, in terms of H*(10), by the experimental results. Recommendations for radiological protection include replicating accidental exposures with WENDI-II and LUPIN-II to estimate doses accurately.