Thermal neutron detection and track recognition method in reference and out-of-field radiotherapy FLASH electron fields using Timepix3 detectors

Abstract

Objective. This work presents a method for enhanced detection, imaging, and measurement of the thermal neutron flux. Approach. Measurements were performed in a water tank, while the detector is positioned out-of-field of a 20 MeV ultra-high pulse dose rate electron beam. A semiconductor pixel detector Timepix3 with a silicon sensor partially covered by a 6LiF neutron converter was used to measure the flux, spatial, and time characteristics of the neutron field. To provide absolute measurements of thermal neutron flux, the detection efficiency calibration of the detectors was performed in a reference thermal neutron field. Neutron signals are recognized and discriminated against other particles such as gamma rays and x-rays. This is achieved by the resolving power of the pixel detector using machine learning algorithms and high-resolution pattern recognition analysis of the high-energy tracks created by thermal neutron interactions in the converter. Main results. The resulting thermal neutrons equivalent dose was obtained using conversion factor (2.13(10) pSv·cm2) from thermal neutron fluence to thermal neutron equivalent dose obtained by Monte Carlo simulations. The calibrated detectors were used to characterize scattered radiation created by electron beams. The results at 12.0 cm depth in the beam axis inside of the water for a delivered dose per pulse of 1.85 Gy (pulse length of 2.4 μs) at the reference depth, showed a contribution of flux of 4.07(8) × 103 particles·cm−2·s−1 and equivalent dose of 1.73(3) nSv per pulse, which is lower by ∼9 orders of magnitude than the delivered dose. Significance. The presented methodology for in-water measurements and identification of characteristic thermal neutrons tracks serves for the selective quantification of equivalent dose made by thermal neutrons in out-of-field particle therapy.

Particle tracking, recognition and LET evaluation of out-of-field proton therapy delivered to a phantom with implants

“…When a charged particle interacts with the pixelated sensor of the TPX3, its energy diffuses in both directions, lateral and horizontal, producing a particular track for that particle called 'cluster' . Having this kind of infrastructure, the semiconductor Timepix-based detectors can discriminate different particle types based on the properties and morphology of each cluster (Vykydal et al 2006, Oancea et al 2023b.…”

“…Notably, no thermal neutrons were measured at the detector position. Based on the limited Si sensor's response to the neutron's detection some dedicated converter should be placed on the active surface to detect them and analyze their impact on the deposited energy (Granja et al 2023b, Oancea et al 2023b. For this reason, this study presents some limitations regarding the detection and spectral characterization of neutrons where only direct interactions in Si were detected, none of this convertor being used in the current experiment.…”

Data Processing Engine (DPE): data analysis tool for particle tracking and mixed radiation field characterization with pixel detectors Timepix

“…The Timepix family of hybrid semiconductor pixelated detectors, including Timepix1 (TPX), Timepix3 (TPX3), and Timepix2 (TPX2), has proven to be a reliable tool for radiation spectrometry and particle tracking [1,2]. These detectors offer the unique advantage of precise energy measurements and time-stamping capabilities, making them highly adaptable to a wide range of scientific and industrial applications such as space radiation monitoring [3], particle radiotherapy [4,5], imaging with X-rays and particles [10,11], Compton camera, radiation tracking [7], dosimetry [9], neutron detection [4,6], etc. Despite their vast potential, the complex data generated by Timepix detectors necessitates the development of advanced data processing techniques to explore their full potential.…”