Speaker
Description
Boron Neutron Capture Therapy (BNCT) is a binary radiotherapy using 10B(n,a)7Li reaction to kill cancer cells with 10B uptake when irradiated with thermal neutrons. The transition from reactor to accelerator-based neutron production has renewed global interest in BNCT, with 80% of the world’s 33 operational facilities using accelerator-based systems. Real-time neutron detectors for thermal flux measurements and RBE prediction are essential for advancing BNCT Quality Assurance.
Our study evaluates microscopic-sized detectors (MOSFET-based ‘MOSkin’ and SOI Microdosimeter), developed by CMRP at UOW, that mimic the scale of human cells and the way radiation interacts within them. Experiments were performed at the Kansai BNCT Medical Center (Osaka, Japan) using the linear array of 5 MOSFETs [1] with pitch 5mm centered in a beam axis and orthogonal to the beam and SOI microdosimeter MicroPlus2 [2] both in a waterproof PMMA sheath, positioned in water phantom. Both the MOSFETs and the SOI microdosimeters of varying thickness of the cylindrical sensitive volumes (SV) of height 10µm, 5µm and 2µm and diameter 20µm were covered with an enriched 10B carbide film 1µm thickness [3] (equivalent 759,000ppm 10B, with 300µm air gap above SVs), mimicking uptake of 10B on a cell surface. Geant4 Monte Carlo simulations were used to compare with experimental data.
The results show excellent agreement within 5% of measured the thermal neutron flux with MOSFET array vs depth in water with calculated by Monte Carlo has been observed. Microdosimetric spectra are dominated by high lineal energy (very high ppm) 10B capture events peak with yD; 42.4, 84.8, and 146.6 keV/µm corresponding to 10, 5, and 2µm SOI microdosimeter and in agreement with G4 simulations demonstrating that in 2µm thick SV most events are crossers. These results confirm the expectations from previous simulation studies [4, 5].
These are the first experimental results using SOI Mushroom microdosimeter in BNCT facility, which demonstrate that the SOI microdosimeter can be used for active real-time measurement of different dose components in BNCT. SOI microdosimeter and MOSkin covered with 10B film measure relative dose as function of depth, providing a real-time relative reading of the thermal neutron component. Next generation of the SOI microdosimeters will be coated with 40-100 ppm 10B during fabrication.
[1]. Rosenfeld A B (2016), “Novel detectors for silicon based microdosimetry”, NIM Sec. A 809.
[2]. Tran L T (2022), “Silicon 3D Microdosimeters for Advanced QA in Particle Therapy”, Applied Sciences, 12(1), 238.
[3]. Höglund C (2012), “B4C thin films for neutron detection”, Journal of Applied Physics 111.
[4]. Vohradsky J (2019), “Evaluation of silicon based microdosimetry for BNCT QA”, Physica Medica 66.
[5]. Hu N (2018), “Feasibility study 3D silicon microdosimeter for microdosimetric analysis in BNCT”, Appl. Radiat. Isot. 140.