Browsing by Author "James, B"

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    3D sensitive volume microdosimeter with improved tissue equivalency: charge collection study and its application in 12C ion therapy
    (IOP Publishing, 2018-02-06) James, B; Tran, LT; Bolst, D; Prokopovich, DA; Reinhard, MI; Lerch, MLF; Petasecca, M; Guatelli, S; Povoli, M; Kok, A; Matsufuji, N; Jackson, M; Rosenfeld, AB
    This research focuses on the characterisation of a new 3D sensitive volume (SV) microdosimeter covered with polyimide – a material which closely mimics human tissue. The electrical and charge collection properties of the device were investigated and its application in 12C ion therapy were studied. Charge collection studies revealed uniform charge collection and no cross talk between adjacent SVs. To study the microdosimetric response in 12C ion therapy, the new polyimide mushroom microdosimeter were placed at various positions along the central axis of a 290 MeV/u 12C ion spread out Bragg peak (SOBP) at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. From these microdosimetric spectra, dose mean lineal energy $(\overline{{y}_{D})}$ and RBE10 results were obtained, with RBE10 increasing from 1.3 at the entrance to 2.7 at the end of the SOBP. The results obtained in this work show that the new generation of mushroom microdosimeters, covered with tissue equivalent polyimide material, are a useful tool for quality assurance in heavy ion therapy applications. © Open Access - CC BY - IOP Publishing Ltd.
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    Application of an SOI microdosimeter for monitoring of neutrons in various mixed radiation field environments
    (Institute of Electrical and Electronics Engineers (IEEE), 2022-03-01) Pan, VA; Vohradsky, J; James, B; Pagani, F; Chartier, L; Debrot, E; Pastuovic, Z; Cutajar, D; Poder, J; Nancarrow, M; Pereloma, E; Bolst, D; Lee, SH; Inaniwa, T; Safavi-Naeini, M; Prokopovich, DA; Guatelli, S; Petasecca, M; Lerch, MLF; Povoli, M; Kok, A; Tran, LT; Rosenfeld, AB
    Radiation monitoring in space radiation is complex due to galactic cosmic rays (GCRs), solar particle events (SPEs), and albedo particles. Thermal neutrons are an important component in the Moon radiation albedo field which can cause single event upset (SEU) in electronics when they interact with the 10 B present in electronic components. In this work, we studied an application of silicon on insulator (SOI) microdosimeters for neutron monitoring in various mixed radiation field environments. A 10- μm SOI microdosimeter was utilized in conjunction with a 10 B 4 C thin-film converter to successfully measure the thermal neutron contribution out of field of a therapeutic proton beam as well as an 18-MV X-ray linear accelerator (LINAC). The microdosimeter was placed downstream of the Bragg peak (BP) as well as laterally out of field of the proton beam and at two positions along the treatment couch of the 18-MV LINAC. It was demonstrated that the 10- μm SOI microdosimeter with 10 B 4 C converter is suitable for detection of thermal neutrons with excellent discrimination of gamma, fast and thermal neutron components in the presence of a gamma-neutron pulsed field of an 18-MV LINAC. To reduce the gamma contribution and further improve detection of neutrons in mixed radiation fields, a new 2 μm Mushroom-planar microdosimeter was fabricated and characterized in detail using an ion beam induced charge collection (IBIC) technique with 1.78 MeV He2+ ions. It was demonstrated that this 2 μm SOI microdosimeter can be operated in a passive mode. The SOI microdosimeter with the 10 B 4 C converter can be recommended for the detection of thermal neutrons for SEU prediction in the mixed gamma-neutron fields during space missions, especially for the Moon mission.© Copyright 2025 IEEE
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    Experimental investigation of the characteristics of radioactive beams for heavy ion therapy
    (Wiley, 2020-07) Chacon, A; James, B; Tran, LT; Guatelli, S; Chartier, L; Prokopovich, DA; Franklin, DR; Mohammadi, A; Nishikido, F; Iwao, Y; Akamatsu, G; Takyu, S; Tashima, H; Yamaya, T; Parodi, K; Rosenfeld, AB; Safavi-Naeini, M
    Purpose This work has two related objectives. The first is to estimate the relative biological effectiveness of two radioactive heavy ion beams based on experimental measurements, and compare these to the relative biological effectiveness of corresponding stable isotopes to determine whether they are therapeutically equivalent. The second aim is to quantitatively compare the quality of images acquired postirradiation using an in‐beam whole‐body positron emission tomography scanner for range verification quality assurance. Methods The energy deposited by monoenergetic beams of C at 350 MeV/u, O at 250 MeV/u, C at 350 MeV/u, and O at 430 MeV/u was measured using a cruciform transmission ionization chamber in a water phantom at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. Dose‐mean lineal energy was measured at various depths along the path of each beam in a water phantom using a silicon‐on‐insulator mushroom microdosimeter. Using the modified microdosimetric kinetic model, the relative biological effectiveness at 10% survival fraction of the radioactive ion beams was evaluated and compared to that of the corresponding stable ions along the path of the beam. Finally, the postirradiation distributions of positron annihilations resulting from the decay of positron‐emitting nuclei were measured for each beam in a gelatin phantom using the in‐beam whole‐body positron emission tomography scanner at HIMAC. The depth of maximum positron‐annihilation density was compared with the depth of maximum dose deposition and the signal‐to‐background ratios were calculated and compared for images acquired over 5 and 20 min postirradiation of the phantom. Results In the entrance region, the was 1.2 ± 0.1 for both C and C beams, while for O and O it was 1.4 ± 0.1 and 1.3 ± 0.1, respectively. At the Bragg peak, the was 2.7 ± 0.4 for C and 2.9 ± 0.4 for C, while for O and O it was 2.7 ± 0.4 and 2.8 ± 0.4, respectively. In the tail region, could only be evaluated for carbon; the was 1.6 ± 0.2 and 1.5 ± 0.1 for C and C, respectively. Positron emission tomography images obtained from gelatin targets irradiated by radioactive ion beams exhibit markedly improved signal‐to‐background ratios compared to those obtained from targets irradiated by nonradioactive ion beams, with 5‐fold and 11‐fold increases in the ratios calculated for the O and C images compared with the values obtained for O and C, respectively. The difference between the depth of maximum dose and the depth of maximum positron annihilation density is 2.4 ± 0.8 mm for C, compared to −5.6 ± 0.8 mm for C and 0.9 ± 0.8 mm for O vs −6.6 ± 0.8 mm for O. Conclusions The values for C and O were found to be within the 95% confidence interval of the RBEs estimated for their corresponding stable isotopes across each of the regions in which it was evaluated. Furthermore, for a given dose, C and O beams produce much better quality images for range verification compared with C and O, in particular with regard to estimating the location of the Bragg peak. © 2024 American Association of Physicists in Medicine.
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    IBIC microscopy – the powerful tool for testing micron – sized sensitive volumes in segmented radiation detectors used in synchrotron microbeam radiation and hadron therapies
    (Elsevier B. V., 2019-11-01) Pastuovic, Z; Davis, J; Tran, LT; Paino, JR; Dipuglia, A; James, B; Povoli, M; Kok, A; Perevertaylo, VL; Siegele, R; Prokopovich, DA; Lerch, MLF; Petasecca, M; Rosenfeld, AB; Cohen, DD
    Ion Beam Induced Charge (IBIC) microscopy performed using highly tuned microbeams of accelerated ions with energies in the MeV range is the powerful tool for analysis of charge carrier transport properties in semiconductor devices based on semiconductor hetero-junction, metal-on-semiconductor and semiconductor-on-insulator configurations. Here we present two cases of recent applications of the IBIC microscopy in the field of medical radiation physics. The reduced-rate ion microbeams with energies in the MeV range and sub-micrometer spot-sizes have been used for the investigations of the charge collection efficiency (CCE) in sensitive volumes of segmented radiation detectors in order to measure the spatial distribution and uniformity of CCE in different polarization conditions. This information allows the determination of the charge carrier transport properties in selected substructures of a particular device and to quantify its ability to accurately determine the energy deposited by incident ionizing radiation - two fundamental requirements of any microdosimeter or detector of ionizing radiation. © 2019 Elsevier B.V.
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    Solid-state microdosimeter for personal radon dosimetry in mines and caves
    (ICRP, 2019-11-17) Tran, LT; James, B; Prokopovich, DA; Boardman, DA; Werczynski, S; Chambers, SD; Waring, CL; Williams, AG; Povoli, M; Lok, A; Jackson, M; Rosefeld, AB
    Radon gas can be found naturally from the materials in which it is formed that contain traces of uranium, actinium, thorium, or neptunium. Uranium and radium are commonly found in soil, rocks and water, especially in enclosed spaces such as mines, caves, cellars or poorly ventilated houses. Radon levels found in uranium, coal and metal mines, especially underground mines, can be up to orders of magnitude above ambient outdoor levels. Radon progeny attach easily to dust particles that can deposit in the lungs when inhaled. Once deposited in the lungs, the radon progeny emits alpha particles, mostly from short lived isotopes 218Po (T1/2 = 3.1 min, E = 6 MeV) and 214Po (T1/2=164.3 µs, E = 7.7 MeV), irradiating and damaging the DNA of lungs or proximal organ tissue, which may increase the risk of developing lung cancer - the second most common cause after smoking. Therefore monitoring radon levels in mines and caves is strictly required in order to protect workers from the health effects of radon exposure. Current radon detectors are bulky, expensive and only measure radon concentration, requiring conversion from concentration to dose which can result in large uncertainties [1]. This work presents a newly developed portable silicon on insulator (SOI) microdosimeter system for use in radon rich environments to measure the dose equivalent caused by 222Rn and its decay progeny. The microdosimeter used in this work is the Mushroom microdosimeters invented and developed by the CMRP, University of Wollongong and fabricated in collaboration with SINTEF MiNaLab, Oslo, Norway. The detector system directly measures in real time dose equivalent H(µSv/h) in a 222Rn gas environment rather than its calculation based on radon activity and dose conversion factor (DCF) as currently. The experiment was carried out at ANSTO environment lab where 245 kBq 226Ra source provides a radon concentration of approximately 150kBq/m3. A dose rate equivalent of 15.4 mSv/h and average quality factor ( ) of 19.96 was measured by the microdosimeter system for the given radon concentration. This result demonstrated that the microdosimeter system can be used in caves, mines for radon dose equivalent monitoring. Miniaturization of electronic personal microdosimeter is in progress and the preliminary results will be presented at the conference.