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Experimental microdosimetry along with the microdosimetric kinetic (MK) model can be utilized to predict the biological effects of ions. To predict the relative biological effectiveness (RBE) of ions and the survival fraction (SF) of human salivary gland tumour (HSGc-C5) cells, microdosimetric quantities measured by a silicon-on-insulator (SOI) MicroPlus-mushroom microdosimeter along the spread-out Bragg peak (SOBP) delivered by pencil beam scanning of 4He, 12C, 16O, and 20Ne ions were used. The MK model parameters of HSGc-C5 cells were obtained from the best fit of the calculated SF for the different linear energy transfer (LET) of these ions and the formerly reported in vitro SF for the same LET and ions used for calculations. For a cube-shaped target of 10 × 10 × 6 cm3, treatment plans for 4He, 12C, 16O, and 20Ne ions were produced with proprietary treatment planning software (TPS) aiming for 10% SF of HSGc-C5 cells over the target volume and were delivered to a polymethyl methacrylate (PMMA) phantom. Afterwards, the saturation-corrected dose-mean lineal energy derived based on the measured microdosimetry spectra, along with the physical dose at various depths in PMMA phantoms, was used for the estimation of the SF, RBE, and RBE-weighted dose using the MK model. The predicted SF, RBE, and the RBE-weighted dose agreed with what was planned by the TPS within 3% at most depths for these ions. [ABSTRACT FROM AUTHOR]

The Centre for Medical Radiation Physics introduced the concept of Silicon On Insulator (SOI) microdosimeters with 3-Dimensional (3D) cylindrical sensitive volumes (SVs) mimicking the dimensions of cells in an array. Several designs of high-definition 3D SVs fabricated using 3D MEMS technology were implemented. 3D SVs were fabricated in different sizes and configurations with diameters between 18 and 30 µm, thicknesses of 2–50 µm and at a pitch of 50 µm in matrices with volumes of 20 × 20 and 50 × 50. SVs were segmented into sub-arrays to reduce capacitance and avoid pile up in high-dose rate pencil beam scanning applications. Detailed TCAD simulations and charge collection studies in individual SVs have been performed. The microdosimetry probe (MicroPlus) is composed of the silicon microdosimeter and low-noise front–end readout electronics housed in a PMMA waterproof sheath that allows measurements of lineal energies as low as 0.4 keV/µm in water or PMMA. Microdosimetric quantities measured with SOI microdosimeters and the MicroPlus probe were used to evaluate the relative biological effectiveness (RBE) of heavy ions and protons delivered by pencil-beam scanning and passive scattering systems in different particle therapy centres. The 3D detectors and MicroPlus probe developed for microdosimetry have the potential to provide confidence in the delivery of RBE optimized particle therapy when introduced into routine clinical practice. [ABSTRACT FROM AUTHOR]

Purpose: A 5 and 10 μm thin silicon on insulator (SOI) 3D mushroom microdosimeter was used to characterize both the in‐field and out‐of‐field of a 62 MeV proton beam. Methods: The SOI mushroom microdosimeter consisted of an array of cylindrical sensitive volumes (SVs), developed by the Centre for Medical Radiation Physics, University of Wollongong, was irradiated with 62 MeV protons at the CATANA (Centro di AdroTerapia Applicazioni Nucleari Avanzate) facility in Catania, Italy, a facility dedicated to the radiation treatment of ocular melanomas. Dose mean lineal energy, (yD¯), values were obtained at various depths in PMMA along a pristine and spread out Bragg peak (SOBP). The measured microdosimetric spectra at each position were then used as inputs into the modified Microdosimetric Kinetic Model (MKM) to derive the RBE for absorbed dose in a middle of the SOBP 2Gy (RBED). Microdosimetric spectra were obtained with both the 5 and 10 μm 3D SOI microdosimeters, with a focus on the distal part of the BP. The in‐field and out‐of‐field measurement configurations along the Bragg curve were modeled in Geant4 for comparison with experimental results. Lateral out‐of‐field measurements were performed to study secondary particles' contribution to normal tissue's dose, up to 12 mm from the edge of the beam field, and quality factor and dose equivalent results were obtained. Results: Comparison between experimental and simulation results showed good agreement between one another for both the pristine and SOBP beams in terms of yD¯ and RBED. Though a small discrepancy between experiment and simulation was seen at the entrance of the Bragg curve, where experimental results were slightly lower than Geant4. The dose equivalent value measured 12 mm from the edge of the target volume was 1.27 ± 0.15 mSv/Gy with a Q¯ value of 2.52 ± 0.30, both of which agree within uncertainty with Geant4 simulation. Conclusions: These results demonstrate that SOI microdosimeters are an effective tool to predict RBED in‐field as well as dose equivalent monitoring out‐of‐field to provide insight to probability of second cancer generation. [ABSTRACT FROM AUTHOR]

Despite the low contribution of heavy ions to the total fluence in the space radiation environment, their radiobiological effect on the human body is extremely high. In this article, we investigated the radiation field which resulted from the interaction of galactic cosmic rays (GCRs), specifically some heavy ions and energies, typically encountered in space with a realistic multilayer sample of the International Space Station (ISS) Columbus module’s shielding wall. The quality factor, Q, and the normalized dose equivalent, H, derived from microdosimetric measurements for C, Ne, and Si ions behind different spacecraft wall configurations and materials are presented in this article. Particularly, carbon fiber, polyoxymethylene, and perspex with same areal density compared to currently used aluminum were investigated. [ABSTRACT FROM AUTHOR]

The response of a 5-μm-thin silicon on insulator (SOI) 3-D microdosimeter was investigated for single-event upset applications by measuring the linear energy transfer (LET) of different high LET ions. The charge collection characteristics of the device were performed using the ion beam-induced charge collection (IBIC) technique with 3- and 5.5-MeV He2+ ions incident on the microdosimeter. The microdosimeter was irradiated with 16O, 56Fe, and 124Xe ions and was able to determine the LET within 5% for most configurations apart from 124Xe. It was observed that on average, measured LET was 12% lower for 30-MeV/u 124Xe ion traversing through different thickness Kapton absorbers in comparison to Geant4 simulations. This discrepancy can be partly attributed to uncertainties in the thickness of the energy degraders and the thickness of the SOI layer of the devices. The effects of overlayer thickness variation are not easily observed for ions with much lower LET as O and Fe. Based on that, it is difficult to make conclusion that the plasma effect is observed for 30-MeV/u124Xe ions and further research to be carried out for ion with LET higher than 12 MeV/μm. [ABSTRACT FROM AUTHOR]

An experimental and simulation-based study was performed on a 12C ion minibeam radiation therapy (MBRT) field produced with a clinical broad beam and a brass multi-slit collimator (MSC). Silicon-on-insulator (SOI) microdosimeters developed at the Centre for Medical Radiation Physics (CMRP) with micron sized sensitive volumes were used to measure the microdosimetric spectra at varying positions throughout the MBRT field and the corresponding dose-mean lineal energies and RBE for 10% cell survival (RBE10) were calculated using the modified Microdosimetric Kinetic Model (MKM). An increase in the average RBE10 of ∼30% and 10% was observed in the plateau region compared to broad beam for experimental and simulation values, respectively. The experimental collimator misalignment was determined to be 0.7° by comparison between measured and simulated microdosimetric spectra at varying collimator angles. The simulated dose-mean lineal energies in the valley region between minibeams were found to be higher on average than in the minibeams due to higher LET particles being produced in these regions from the MSC. This work presents the first experimental microdosimetry measurements and characterisation of the local biological effectiveness in a MBRT field. [ABSTRACT FROM AUTHOR]

The responses of two silicon on insulator (SOI) 3-D microdosimeters developed by the Centre for Medical Radiation Physics were investigated with a range of different low energy ions, with high linear energy transfer (LET). The two microdosimeters n-SOI and p-SOI were able to measure the LET of different ions including 7Li, 12C, 16O, and 48Ti with ranges below $350~\mu \text{m}$ in silicon. No plasma effects were seen in the SOI microdosimeters when irradiated with the high LET ions. A Monte Carlo simulation using Geant4 was compared to the experimental measurements, whereby some discrepancies were observed for heavier ions at lower energies. This discrepancy can be partly attributed to uncertainties in the thickness of the energy degraders and overlayers of the devices. The microdosimetric measurements of low energy 16O ions were obtained and compared to a therapeutic 16O ion beam. The radiation hardness of the two devices was studied using the ion beam induced charge collection technique. Both types of the microdosimeters when biased had no essential changes in charge collection efficiency in the sensitive volume after irradiation with low energy ions. [ABSTRACT FROM AUTHOR]

Background: The aim of this study was to measure the microdosimetric distributions of a carbon pencil beam scanning (PBS) and passive scattering system as well as to evaluate the relative biological effectiveness (RBE) of different ions, namely 12C, 14N, and 16O, using a silicon‐on‐insulator (SOI) microdosimeter with well‐defined 3D‐sensitive volumes (SV). Geant4 simulations were performed with the same experimental setup and results were compared to the experimental results for benchmarking. Method: Two different silicon microdosimeters with rectangular parallelepiped and cylindrical shaped SVs, both 10 μm in thickness were used in this study. The microdosimeters were connected to low noise electronics which allowed for the detection of lineal energies as low as 0.15 keV/μm in tissue. The silicon microdosimeters provide extremely high spatial resolution and can be used for in‐field and out‐of‐field measurements in both passive scattering and PBS deliveries. The response of the microdosimeters was studied in 290 MeV/u 12C, 180 MeV/u 14N, 400 MeV/u 16O passive ion beams, and 290 MeV/u 12C scanning carbon therapy beam at heavy ion medical accelerator in Chiba (HIMAC) and Gunma University Heavy Ion Medical Center (GHMC), Japan, respectively. The microdosimeters were placed at various depths in a water phantom along the central axis of the ion beam, and at the distal part of the Spread Out Bragg Peak (SOBP) in 0.5 mm increments. The RBE values of the pristine Bragg peak (BP) and SOBP were derived using the microdosimetric lineal energy spectra and the modified microdosimetric kinetic model (MKM), using MKM input parameters corresponding to human salivary gland (HSG) tumor cells. Geant4 simulations were performed in order to verify the calculated depth‐dose distribution from the treatment planning system (TPS) and to compare the simulated dose‐mean lineal energy to the experimental results. Results: For a 180 MeV/u 14N pristine BP, the dose‐mean lineal energy y D ¯ obtained with two types of silicon microdosimeters started from approximately 29 keV/μm at the entrance to 92 keV/μm at the BP, with a maximum value in the range of 412 to 438 keV/μm at the distal edge. For 400 MeV/u 16O ions, the dose‐mean lineal energy y D ¯ started from about 24 keV/μm at the entrance to 106 keV/μm at the BP, with a maximum value of approximately 381 keV/μm at the distal edge. The maximum derived RBE10 values for 14N and 16O ions were found to be 3.10 ± 0.47 and 2.93 ± 0.45, respectively. Silicon microdosimetry measurements using pencilbeam scanning 12C ions were also compared to the passive scattering beam. Conclusions: These SOI microdosimeters with well‐defined three‐dimensional (3D) SVs have applicability in characterizing heavy ion radiation fields and measuring lineal energy deposition with sub‐millimeter spatial resolution. It has been shown that the dose‐mean lineal energy increased significantly at the distal part of the BP and SOBP due to very high LET particles. Good agreement was observed for the experimental and simulation results obtained with silicon microdosimeters in 14N and 16O ion beams, confirming the potential application of SOI microdosimeter with 3D SV for quality assurance in charged particle therapy. [ABSTRACT FROM AUTHOR]

New 10- \mu \textm -thick silicon microdosimeters utilizing 3-D technology have been developed and investigated in this paper. The TCAD simulations were carried out to understand the electrical properties of the microdosimeters’ design. A charge collection study of the devices was performed using 5.5-MeV He2+ ions which were raster scanned over the surface of the detectors and the charge collection median energy maps were obtained and the detection yield was also evaluated. The devices were tested in a 290 MeV/u carbon ion beam at the Heavy Ion Medical Accelerator in Chiba (HIMAC) in Japan. Based on the microdosimetric measurements, the quality factor and dose equivalent out of field were obtained in a mixed radiation field mimicking the radiation environment for spacecraft in deep space. [ABSTRACT FROM PUBLISHER]

Purpose This work aims to characterize a proton pencil beam scanning ( PBS) and passive double scattering ( DS) systems as well as to measure parameters relevant to the relative biological effectiveness ( RBE) of the beam using a silicon on insulator ( SOI) microdosimeter with well-defined 3D sensitive volumes ( SV). The dose equivalent downstream and laterally outside of a clinical PBS treatment field was assessed and compared to that of a DS beam. Methods A novel silicon microdosimeter with well-defined 3D SVs was used in this study. It was connected to low noise electronics, allowing for detection of lineal energies as low as 0.15 keV/μm. The microdosimeter was placed at various depths in a water phantom along the central axis of the proton beam, and at the distal part of the spread-out Bragg peak ( SOBP) in 0.5 mm increments. The RBE values of the pristine Bragg peak ( BP) and SOBP were derived using the measured microdosimetric lineal energy spectra as inputs to the modified microdosimetric kinetic model ( MKM). Geant4 simulations were performed in order to verify the calculated depth-dose distribution from the treatment planning system ( TPS) and to compare the simulated dose-mean lineal energy to the experimental results. Results For a 131 MeV PBS spot (124.6 mm R90 range in water), the measured dose-mean lineal energy [ABSTRACT FROM AUTHOR]

Purpose Microdosimetry is a vital tool for assessing the microscopic patterns of energy deposition by radiation, which ultimately govern biological effect. Solid-state, silicon-on-insulator microdosimeters offer an approach for making microdosimetric measurements with high spatial resolution (on the order of tens of micrometers). These high-resolution, solid-state microdosimeters may therefore play a useful role in characterizing proton radiotherapy fields, particularly for making highly resolved measurements within the Bragg peak region. In this work, we obtain microdosimetric measurements with a solid-state microdosimeter (MicroPlus probe) in a clinical, spot-scanning proton beam of small spot size. Methods The MicroPlus probe had a 3D single sensitive volume on top of silicon oxide. The sensitive volume had an active cross-sectional area of 250 μm × 10 μm and thickness of 10 μm. The proton facility was a synchrotron-based, spot-scanning system with small spot size ( σ ≈ 2 mm). We performed measurements with the clinical beam current (≈1 nA) and had no detected pulse pile-up. Measurements were made in a water-equivalent phantom in water-equivalent depth (WED) increments of 0.25 mm or 1.0 mm along pristine Bragg peaks of energies 71.3 MeV and 159.9 MeV, respectively. For each depth, we measured lineal energy distributions and then calculated the dose-weighted mean lineal energy [ABSTRACT FROM AUTHOR]

This paper presents an overview of the development of semiconductor microdosimetry and the most current (state-of-the-art) Silicon on Insulator (SOI) detectors for microdosimetry based mainly on research and development carried out at the Centre for Medical Radiation Physics (CMRP) at the University of Wollongong with collaborators over the last 18 years. In this paper every generation of CMRP SOI microdosimeters, including their fabrication, design, and electrical and charge collection characterisation are presented. A study of SOI microdosimeters in various radiation fields has demonstrated that under appropriate geometrical scaling, the response of SOI detectors with the well-known geometry of microscopically sensitive volumes will record the energy deposition spectra representative of tissue cells of an equivalent shape. This development of SOI detectors for microdosimetry with increased complexity has improved the definition of microscopic sensitive volume (SV), which is modelling the deposition of ionising energy in a biological cell, that are led from planar to 3D SOI detectors with an array of segmented microscopic 3D SVs. The monolithic Δ E − E silicon telescope, which is an alternative to the SOI silicon microdosimeter, is presented, and as an example, applications of SOI detectors and Δ E − E monolithic telescope for microdosimetery in proton therapy field and equivalent neutron dose measurements out of field are also presented. An SOI microdosimeter “bridge” with 3D SVs can derive the relative biological effectiveness (RBE) in 12 C ion radiation therapy that matches the tissue equivalent proportional counter (TEPC) quite well, but with outstanding spatial resolution. The use of SOI technology in experimental microdosimetry offers simplicity (no gas system or HV supply), high spatial resolution, low cost, high count rates, and the possibility of integrating the system onto a single device with other types of detectors. [ABSTRACT FROM AUTHOR]

This paper presents a new version of the 3D mesa Bridge microdosimeter comprised of an array of 4248 silicon cells fabricated on \10~\mu\m thick n-type silicon-on-insulator substrate. This microdosimeter has been designed to overcome limitations existing in previous generation silicon microdosimeters and it provides well-defined sensitive volumes and high spatial resolution. The charge collection characteristics of the new 3D mesa microdosimeter were investigated using the ANSTO heavy ion microprobe, utilizing \5.5~MeV\ He^2 + ions. Measurement of microdosimetric quantities allowed for the determination of the relative biological effectiveness of 290 MeV/u and 350~\MeV/u\ ^12C heavy ion therapy beams at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. The microdosimetric RBE obtained showed good agreement with the tissue-equivalent proportional counter. Utilizing the high spatial resolution of the SOI microdosimeter, the LET spectra for \70~MeV\ ^12C^ + 6 ions, like those present at the distal edge of 290 and 350 MeV/u beams, were obtained as the ions passed through thin layers of polyethylene film. This microdosimeter can provide useful information about the lineal energy transfer (LET) spectra downstream of the protective layers used for shielding of electronic devices for single event upset prediction. [ABSTRACT FROM PUBLISHER]

The tissue-equivalent proportional counter is the gold standard detector in microdosimetry. The energy deposited in its volume is equal to that of a single cell through the use of low pressure tissue-equivalent gas. To overcome its bulky gas-flow ensemble, high operating voltage and poor spatial resolution, a 20 \mum-thick silicon microdosimeter with 9600 micron-sized sensitive volumes has been developed. Presented are the results from its initial characterization including electrical properties and charge collection characteristics obtained using induced charge collection techniques at ANSTO, Australia, and the ESRF, France. In addition, the results from a 290 MeV/u C-12 irradiation at HIMAC, NIRS, Japan, are presented. [ABSTRACT FROM PUBLISHER]

Microdosimetry is an extremely useful technique, used for dosimetry in unknown mixed radiation fields typical of space and aviation, as well as in hadron therapy. A new silicon microdosimeter with 3D sensitive volumes has been proposed to overcome the shortcomings of the conventional Tissue Equivalent Proportional Counter. In this article, the charge collection characteristics of a new 3D mesa microdosimeter were investigated using the ANSTO heavy ion microprobe utilizing 5.5 MeV He^2 + and 2 MeV H^ + ions. Measurement of the microdosimetric characteristics allowed for the determination of the Relative Biological Effectiveness of the ^12C heavy ion therapy beam at the Heavy Ion Medical Accelerator in Chiba (HIMAC), Japan. Well-defined sensitive volumes of the 3D mesa microdosimeter have been observed and the microdosimetric RBE obtained showed good agreement with the TEPC. The new 3D mesa “bridge” microdosimeter is a step forward towards a microdosimeter with fully free-standing 3D sensitive volumes. [ABSTRACT FROM PUBLISHER]

An ultra-thin 3-D detector (U3DTHIN) with a 10-\mum-thick active region has been proposed to apply for microdosimetry in heavy ion therapy where the ion beam incidence is normal to the detector. The advantage of the detector is that the detector substrate below the silicon-on-insulator layer has been etched away. Extremely small columnar 3-D electrodes allow the detector to be fully depleted at very low biases with a minimum dead region due to their size. In this paper, a charge collection study of the U3DTHIN detector carried out using an ion beam-induced charge collection (IBICC) technique is presented. The IBICC study utilized a microbeam of 5.5 MeV He^2 + and 20 MeV^12C ions focused to approximately 1-\mum diameter. Full charge collection was observed from a bias as low as -10 V. A comparison of the detector response when irradiated from the front and rear side is also presented. [ABSTRACT FROM PUBLISHER]

A diamond microdosimeter prototype with sensitive volumes separated through laser milled trenches is characterized. It is proposed that this design will offer a new and alternative means of creating a diamond based microdosimeter. The device has been characterized by means of ion beam induced charge collection (IBIC) measurements. In this work, it is shown that laser milled trenches have a significant effect upon the lateral confinement of charge collection essentially creating a pixelated diamond detector. Specifics of the results and an update on the current status of the project are presented. [ABSTRACT FROM PUBLISHER]

A study of charge collection in SINTEF 3D active edge silicon detectors was carried out at ANSTO using Ion Beam Induced Charge (IBIC) technique. An IBIC study has shown that several different geometries of 3D detectors have full depletion under low applied bias. The effect of fast neutron and gamma radiation on their charge collection efficiency was also investigated. A 3D active edge silicon detector technology has demonstrated extremely promising performance for application of the 3D Sensitive Volumes (SVs) fabrication methods to SOI microdosimetry. [ABSTRACT FROM PUBLISHER]

Radiation detectors based on diamond are attractive for radiation protection applications in space and aviation due to their radiation hardness, large breakdown voltage, fast signal collection, and low noise, thus representing a valid alternative to silicon-based detector devices. In this paper, we study the tissue equivalence of diamond in proton and \alpha particle radiation fields typical of galactic cosmic rays and solar particle events. We determine a method to convert microdosimetric response from diamond to water by means of Geant4 simulations. Results are presented showing that a simple geometrical scaling factor (\sim 0.32) of linear dimensions is adequate to convert experimentally obtained microdosimetric energy deposition spectra in diamond to equivalent microdosimetric energy deposition spectra in water. [ABSTRACT FROM PUBLISHER]

A 4th generation silicon microdosimeter has been designed by the Centre for Medical Radiation Physics (CMRP) at the University of Wollongong using three dimensional (3D) Sensitive Volumes (SVs). This new microdosimeter design has the advantage of well-defined 3D SVs as well as the elimination of lateral charge diffusion by removal of silicon laterally adjacent to the 3D SVs. The gaps between the sensitive volumes are to be backfilled with PolyMethyl MethAcrylate (PMMA) to produce a surrounding tissue equivalent medium. The advantage of this design avoids the generation of secondary particles from inactive silicon lateral to SVs. The response of the microdosimeter to the neutron field from ^252Cf, Pu-Be sources and an avionic radiation environment were simulated using the Geant4 Monte Carlo toolkit for design optimisation. The simulated energy deposition in the SVs from the neutron fields and microdosimetric spectra is presented. The simulation study shows a significant reduction in silicon nuclear recoil contribution to the energy deposition for the novel microdosimeter design. The reduction of silicon recoil events from outside of the SV’s will consequently reduce the uncertainty in the calculated dose equivalent. The simulations have demonstrated that a 3D silicon microdosimeter surrounded by PMMA can produce microdosimetric spectra similar to those of a tissue equivalent microdosimeter. [ABSTRACT FROM PUBLISHER]

An n-SOI microdosimeter which has been proposed as a device for predicting the occurrence of single event effects in semiconductor electronics in the high-energy, mixed heavy ion space radiation environment has been investigated to better understand the charge collection geometry and charge collection mechanisms. Ion beam induced charge collection studies using 20 MeV ^12C ions, 5.5 MeV ^4He ions, and 2 MeV H ions were carried out, and the effects of different bias conditions, angles of ion incidence, and coincidence analysis were observed to understand the sensitive volume geometry. The energy response of the n-SOI microdosimeter has been observed to exhibit an over-response of 56%, 113%, and 23% for the above ions compared to expected energy depositions calculated using SRIM 2008. No relationship between particle LET AU: Please provide spelling for “LET” and the enhance energy response was apparent. A comparison of experimentally measured and simulated spectra suggest a cylindrical charge collection geometry despite the physical rectangular parallelepiped geometry of the p-i-n diode. This was supported by observing the response of the microdosimeter to ions at oblique ion incidence. A simplified model of diffusion charge collection found that diffusion charge collection contributes to the low-energy tail observed in experimental spectra, but does not account for the observed enhanced energy response. This supports the current theory that the enhanced energy response is a result of a displacement current produced when charge carriers in the substrate induce charge in the SOI layer due to the parasitic capacitance of the buried SiO_2 insulating layer. [ABSTRACT FROM PUBLISHER]

This paper is dedicated to the characterization of a novel diamond microdosimeter prototype with 3D sensitive volumes produced by high energy boron implantation. Diamond has been chosen in order to further improve solid state based microdosimeter in terms of radiation hardness and tissue equivalency. IBIC measurements were undertaken to determine the charge collection efficiency map of the device. It was demonstrated that the proposed ion implantation technology allows for the formation of an array of well defined 3D SVs. A Geant4 application was developed to explain the effect of Al electrode thickness on observed anomaly in deposited energy. Specifics of the results and an update on the current status of the project is presented. [ABSTRACT FROM AUTHOR]

Silicon microdosimeters for the characterisation of mixed radiation fields relevant to the space radiation environment have been under continual development at the Centre for Medical Radiation Physics for over a decade. These devices are useful for the prediction of single event upsets in microelectronics and for radiation protection of spacecraft crew. The latest development in silicon microdosimetry is a family of large-area n-SOI microdosimeters for real-time dosimetry in space radiation environments. The response of n-SOI microdosimeters to 2 MeV H and 5.5 MeV He ions has been studied to investigate their charge collection characteristics. The studies have confirmed 100% yield of functioning cells, but have also revealed a charge sharing effect due to diffusion of charge from events occurring outside the sensitive volume and an enhanced energy response due to the collection of charge created beneath the insulating layer. The use of a veto electrode aims to reduce collection of diffused charge. The effectiveness of the veto electrode has been studied via a coincidence analysis using IBIC. It has been shown that suppression of the shared events allows results in a better defined sensitive volume corresponding to the region under the core electrode where the electric field is strongest. [ABSTRACT FROM AUTHOR]

The CERN-EU High Energy Reference Field (CERF) facility is used in the calibration of neutron dosimeters for radiation protection applications in aviation and high energy physics. A comparison of the facility's microdosimetric spectra obtained with a new Silicon on Insulator (SOI) Microdosimeter and a HAWK Tissue Equivalent Proportional Counter (TEPC) is presented. Experimental data obtained with both devices indicates the presence of a small charged particle flux within the neutron dominated field which makes a non negligible contribution to the dose equivalent. [ABSTRACT FROM PUBLISHER]

A novel silicon-on-insulator (SOI) microdosimeter has been designed and fabricated using planar processing techniques to realise a device with a micron-scale well-defined sensitive volume. Cylindrical structures were employed to allow for an improved definition of the average chord length of the sensitive volume over that of previous elongated parallelepiped solid-state detector designs. The structures were manufactured on individual silicon mesas situated on top of a buried oxide insulating layer. The mesa design eliminated lateral charge diffusion. Two kinds of test structures were designed with sensitive region widths of 2 μm and 10 μm. In addition, an array of 900 cylindrical diodes was fabricated to increase the charge collection statistics. TCAD (Technology Computer Aided Design) modeling of the electrostatic potential and electric field profile of the cylindrical microdosimeter was carried out to obtain 3D potential and electric field profiles. The modeling revealed a radial electric field within the cylindrical-shaped sensitive volume with a 1/r dependence. While the electric field at the core of the cylindrical microdosimeter was not sufficiently high to induce avalanche signal multiplication, the higher electric field at the core should still assist in the measurement of low linear-energy transfer (LET) events. [ABSTRACT FROM AUTHOR]

Silicon microdosimetry measurements in Fast Neutron Therapy were simulated using the GEANT4 Monte Carlo toolkit. The possibility of using silicon microdosimeters for verification of Monte Carlo based treatment planning systems in hadron therapy is suggested. [ABSTRACT FROM AUTHOR]

A heavy ion microprobe was used to conduct ion beam induced charge (IBIC) collection imaging of silicon microdosimeters. The GEANT4 Monte Carlo toolkit was used to simulate these measurements to calculate ion energy loss in the device overlayer and energy deposition in the device sensitive volume. A comparison between experimental and theoretical results facilitated the calculation of charge collection efficiency profiles for several ions. [ABSTRACT FROM AUTHOR]

An ion beam induced charge (IBIC) facility has been added to the existing capabilities of the ANSTO heavy ion microprobe and the results of the first measurements are presented. Silicon on insulator (SOI) diode arrays with microscopic junction sizes have recently been proposed as microdosimeters for hadron therapy. A 20 MeV carbon beam was used to perform IBIC imaging of a 10 μm thick SOI device. [Copyright &y& Elsevier]

Abstract A dedicated Geant4 study was developed to determine a correction factor (C) to convert the energy deposition response in diamond to water for heavy charged ions, with atomic number (Z) greater than 2 with energies typical of Galactic Cosmic Rays. The energy deposition response within an ideal diamond based microdosimeter was modelled and converted into a microdosimetric spectrum. The simulation was then repeated, substituting diamond with water. It was shown that by applying the correction factor, the energy deposition and microdosimetric response in diamond could be matched to that of water. The correction factor was determined to be C = 0.32 to 0.33. This study has shown a weak dependence of the correction factor C with respect to the Z of the projectile. The correction factor remains applicable for converting microdosimetric spectra in diamond to water for Galactic Cosmic Rays. This result is extremely encouraging and indicative of the applicability of diamond for use in radioprotection applications in space environments. [ABSTRACT FROM AUTHOR]

This paper presents recent development of Silicon on Insulator (SOI) detectors for microdosimetry at the Centre for Medical Radiation Physics (CMRP) at the University of Wollongong. A new CMRP SOI microdosimeter design, the 3D mushroom microdosimeter is presented. Modification of SOI design and changes to the fabrication processes have led to improved definition of the microscopic sensitive volumes (SV), and thus to better modelling of the deposition of ionizing energy in a biological cell. The electrical and charge collection properties of the devices have been presented in previous works. In this study, the response of the microdosimeters in monoenergetic and spread out Bragg peak therapeutic 12 C ion beam at Heavy Ion Medical Accelerator in Chiba (HIMAC, Japan) are presented. Derived relative biological effectiveness (RBE) in 12 C ion radiation therapy matches the tissue equivalent proportional counter (TEPC) well, along with outstanding spatial resolution. The use of SOI technology in experimental microdosimetry offers simplicity (no gas system or HV supply), high spatial resolution, low cost, high count rates capabilities for beam characterisation and quality assurance (QA) in charged particle therapy. [ABSTRACT FROM AUTHOR]

Nuclear fragmentation produced in 12 C ion therapeutic beams contributes significantly to the Relative Biological Effectiveness (RBE)—weighted dose in the distal edge of the Spread out Bragg Peak (SOBP) and surrounding tissues in out-of-field. Complex mixed radiation field originated by the therapeutic 12 C ion beam in a phantom is difficult to measure. This study presents a new method to characterise the radiation field produced in a 12 C ion beam using a monolithic Δ E-E telescope which provides the capability to identify the particle components of the mixed radiation field as well as the microdosimetric spectra that allows derivation of the RBE based on a radiobiological model. The response of the monolithic Δ E-E telescope to a 290 MeV/u 12 C ion beam at defined positions along the pristine Bragg Peak was studied using the Geant4 Monte Carlo toolkit. The microdosimetric spectra derived from the Δ E stage and the two-dimensional scatter plots of energy deposition in Δ E and E stages of the device in coincidence are presented, as calculated in-field and out-of-field. Partial dose weighted contribution to the microdosimetric spectra from nuclear fragments and recoils, such as 1 H, 4 He, 3 He, 7 Li, 9 Be and 11 B, have been analysed for each position. Comparison of simulation and experimental results are presented and demonstrates that the microdosimetric spectra changes dramatically within 0.5 mm depth increments close to and at the distal edge of the Bragg Peak which is impossible to identify using conventional Tissue Equivalent Proportional Counter (TEPC). [ABSTRACT FROM AUTHOR]

Abstract: Semiconductor planar processing technology has spurned the development of novel radiation detectors with applications in space, high energy physics, medical diagnostics, radiation protection and cancer therapy. The ANSTO heavy ion microprobe, which allows a wide range of ions to be focused into spot sizes of a few micrometers in diameter, has proven to be an essential tool for characterising these detectors using the Ion Beam Induced Charge (IBIC) imaging technique. The use of different ions and the wide range of available energies on the heavy ion microprobe, allows the testing of these devices with ionising particles associated with different values of linear energy transfer (LET). Quadruple coincidence measurements have been used to map the charge collection characteristics of a monolithic ΔE–E telescope. This was done through simultaneous measurement of the spatial coordinates of the microbeam relative to the sample and the response of both detector elements. The resulting charge collection maps were used to better understand the functionality of the device as well as to ascertain ways in which future device designs could be modified to improve performance. [Copyright &y& Elsevier]

The timing properties of a silicon-on-insulator microdosimeter for medical and space applications have been studied using an ion microprobe. These measurements were used with a pulse shape discrimination technique to render the microdosimeter insensitive to ion strikes outside the ideal sensitive volume. [Copyright &y& Elsevier]