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Objective. Microdosimetry offers a fast tool for radiation quality (RQ) verification to be implemented in treatment planning systems in proton therapy based on variable LET or RBE to move forward from the use of a fixed RBE of 1.1. It is known that the RBE of protons can increase up to 50% higher than that value in the last few millimetres of their range. Microdosimetry can be performed both experimentally and by means of Monte Carlo (MC) simulations. This paper has the aim of comparing the two approaches. Approach. Experimental measurements have been performed using a miniaturized Tissue equivalent proportional counter developed at the Legnaro National Laboratories of the Italian National Institute for Nuclear Physics with the aim of being used as RQ monitors for high intensity beams. MC simulations have been performed using the microdosimetric extension of TOPAS which provides optimized parameters and scorers for this application. Main results. Simulations were compared with experimental microdosimetric spectra in terms of shape of the spectra and their average values. Moreover, the latter have been investigated as possible estimators of LET obtained with the same MC code. The shape of the spectra is in general consistent with the experimental distributions and the average values of the distributions in both cases can predict the RQ increase with depth. Significance. This study aims at the comparison of microdosimetric spectra obtained from both experimental measurements and the microdosimetric extension of TOPAS in the same radiation field. [ABSTRACT FROM AUTHOR]

The interest in hadron therapy is growing fast thanks to the latest technological advances in accelerators and delivery technologies, to the development of more and more efficient and comprehensive treatment planning tools, and due to its increasing clinical adoption proving its efficacy. A precise and reliable beam quality assessment and an accurate and effective inclusion of the biological effectiveness of different radiation qualities are fundamental to exploit at best its advantages with respect to conventional radiotherapy. Currently, in clinical practice, the quality assurance (QA) is carried out by means of conventional dosimetry, while the biological effectiveness of the radiation is taken into account considering the Relative Biological Effectiveness (RBE). The RBE is considered a constant value for protons and it is estimated as a function of the absorbed dose in case of carbon ions. In this framework, microdosimetry could bring a significant improvement to both QA and RBE estimation. By measuring the energy deposited by the radiation into cellular or sub-cellular volumes, microdosimetry could provide a unique characterisation of the beam quality on one hand, and a direct link to radiobiology on the other. Different detectors have been developed for microdosimetry, from the more conventional tissue equivalent proportional counter (TEPC), silicon-based and diamond-based solid-state detectors, to ΔE-E telescope detectors, gas electrons multiplier (GEM), hybrid microdosimeters and a micro-bolometer based on Superconducting QUantum Interference Device (SQUID) technology. However, because of their different advantages and drawbacks, a standard device and an accredited experimental methodology have not been unequivocally identified yet. The establishment of accepted microdosimetry standard protocols and code of practice is needed before the technique could be employed in clinical practice. Hoping to help creating a solid ground on which future research, development and collaborations could be planned and inspired, a comprehensive state of the art of the detector technologies developed for microdosimetry is presented in this review, discussing their use in clinical hadron therapy conditions and considering their advantages and drawbacks.

Measurements in the stray radiation field from a proton therapy pencil beam at energies 70 and 146 MeV were performed using microdosimetric tissueequivalent proportional counters (TEPCs). The detector volumes were filled with a propane-based tissue-equivalent gas at low pressure simulating a mean chord length of 2 mmin tissue. Investigations were performed with and without a beam range shifter, and with different air gaps between the range shifter and a solid water phantom. The absorbed dose, the dose-mean lineal energy, and the dose equivalent were determined for different detector positions using the variance-covariance method. The influence from beam energy, detector- and range-shifter positions on absorbed dose, LET, and dose equivalent were investigated. Monte Carlo simulations of the fluence, detector response, and absorbed dose contribution from different particles were performed with MCNP 6.2. The simulated dose response for protons, neutrons, and photons were compared with, and showed good agreement with, previously published experimental data. The simulations also showed that the TEPC absorbed dose agrees well with the ambient absorbed dose for neutron energies above 20 MeV. The results illustrate that changes in both dose and LET variations in the stray radiation field can be identified from TEPC measurements using the variance-covariance method. The results are in line with the changes seen in the simulated relative dose contributions from different particles associated with different proton energies and range-shifter settings. It is shown that the proton contribution scattered directly from the range shifter dominates in some situations, and although the LET of the radiation is decreased, the ambient dose equivalent is increased up to a factor of 3. [ABSTRACT FROM AUTHOR]

Measurements in the stray radiation field from a proton therapy pencil beam at energies 70 and 146 MeV were performed using microdosimetric tissue-equivalent proportional counters (TEPCs). The detector volumes were filled with a propane-based tissue-equivalent gas at low pressure simulating a mean chord length of 2 μm in tissue. Investigations were performed with and without a beam range shifter, and with different air gaps between the range shifter and a solid water phantom. The absorbed dose, the dose-mean lineal energy, and the dose equivalent were determined for different detector positions using the variance–covariance method. The influence from beam energy, detector- and range-shifter positions on absorbed dose, LET, and dose equivalent were investigated. Monte Carlo simulations of the fluence, detector response, and absorbed dose contribution from different particles were performed with MCNP 6.2. The simulated dose response for protons, neutrons, and photons were compared with, and showed good agreement with, previously published experimental data. The simulations also showed that the TEPC absorbed dose agrees well with the ambient absorbed dose for neutron energies above 20 MeV. The results illustrate that changes in both dose and LET variations in the stray radiation field can be identified from TEPC measurements using the variance–covariance method. The results are in line with the changes seen in the simulated relative dose contributions from different particles associated with different proton energies and range-shifter settings. It is shown that the proton contribution scattered directly from the range shifter dominates in some situations, and although the LET of the radiation is decreased, the ambient dose equivalent is increased up to a factor of 3.

Abstract Ionizing radiation at aircraft and commercial suborbital spaceflight altitudes is driven by space weather and is a health concern for crew and passengers. We compare the response functions of two radiation detectors that were exposed to four different ground‐based laboratory radiation fields as well as flown alongside each other on aircraft. The detectors were a tissue equivalent proportional counter (TEPC) and a Teledyne silicon micro dosimeter chip that was integrated into an Automated Radiation Measurements for Aerospace Safety Flight Module (ARMAS FM). Both detectors were flown onboard commercial and research aircraft. In addition, both detectors were exposed neutrons at the Los Alamos Neutron Science Center, protons at Loma Linda University Medical Center, 56Fe particles at the NASA Space Radiation Laboratory, and also a gamma radiation source at Lawrence Livermore National Laboratory. The response of each of these instruments as well as derived dosimetric quantities are compared for each radiation exposure and the ratio for converting ARMAS absorbed dose in silicon to an estimated absorbed dose in tissue is obtained. This process resulted in the first definitive calibration of the silicon‐based detector like ARMAS to TEPC. In particular, with seven flights of both instruments together, the ARMAS‐derived dose in tissue was then validated with the TEPC‐measured dose in tissue and these results are reported. This work provides a method for significantly improving the accuracy of radiation measurements relevant to human tissue safety using a silicon detector that is easy to deploy and can report data in real time.

Clinical guidelines recommend a phase-based approach to treatment for complex post-traumatic stress disorder (CPTSD), yet little is known about what interventions are being offered and which may be effective in the final 'reintegration' phase. To systematically review literature on reintegration interventions for CPTSD, describing the nature and effectiveness of interventions. We searched four electronic databases (Medline, PsycINFO, Embase, and PTSDpubs) for interventions aiming to facilitate reintegration for participants with probable CPTSD. We had two aims: firstly, to describe the interventions and secondly, to describe their effectiveness as measured through measures of reintegration, PTSD and/or disturbances in self-organization (DSO), or qualitative data describing changes experienced. Results are presented using narrative synthesis. Fifteen studies met our inclusion criteria. Interventions included yoga, exercise, use of service dogs, residential treatment, education, self-defence and patient research involvement. Overall study quality was low, as assessed by critical appraisal tools. Of the six studies including a control group, two reported a statistically significant improvement in the measure of reintegration between the intervention and control group, four studies reported a statistically significant difference in the measure of PTSD symptoms, but none reported any significant differences between intervention and control groups in DSO. Of all eight quantitative studies, three reported a statistically significant difference in the reintegration measure pre- to post-intervention for the intervention group, five a statistically significant improvement in the measure of PTSD symptoms, and three a significant difference in the DSO measure. From eight studies reporting qualitative date we synthesized themes into eight categories, within which facilitation of connection with others was the most commonly reported benefit. The interventions outlined may facilitate reintegration, however, research in this area is still in its infancy and quality research is lacking. Further research is needed to establish whether reintegration interventions enhance treatment for CPTSD. A phased-based approach to treating CPTSD has been recommended by experts; however Phase 3 'Reintegration' interventions have been subject to little research. This review showed such interventions may reduce CPTSD symptoms and enhance integration, but research evidence is currently weak. [ABSTRACT FROM AUTHOR]

Ionizing radiation at aircraft and commercial suborbital spaceflight altitudes is driven by space weather and is a health concern for crew and passengers. We compare the response functions of two radiation detectors that were exposed to four different ground‐based laboratory radiation fields as well as flown alongside each other on aircraft. The detectors were a tissue equivalent proportional counter (TEPC) and a Teledyne silicon micro dosimeter chip that was integrated into an Automated Radiation Measurements for Aerospace Safety Flight Module (ARMAS FM). Both detectors were flown onboard commercial and research aircraft. In addition, both detectors were exposed neutrons at the Los Alamos Neutron Science Center, protons at Loma Linda University Medical Center, 56Fe particles at the NASA Space Radiation Laboratory, and also a gamma radiation source at Lawrence Livermore National Laboratory. The response of each of these instruments as well as derived dosimetric quantities are compared for each radiation exposure and the ratio for converting ARMAS absorbed dose in silicon to an estimated absorbed dose in tissue is obtained. This process resulted in the first definitive calibration of the silicon‐based detector like ARMAS to TEPC. In particular, with seven flights of both instruments together, the ARMAS‐derived dose in tissue was then validated with the TEPC‐measured dose in tissue and these results are reported. This work provides a method for significantly improving the accuracy of radiation measurements relevant to human tissue safety using a silicon detector that is easy to deploy and can report data in real time. Key Points: Measurements from a radiation detector based on the Teledyne uDOS001 were cross‐calibrated to measurements from a TEPC microdosimerResults from parallel exposure of these instruments in 4 different radiation fields were utilized to create a new cross‐calibration methodExcellent agreement on seven airline flight measurements was found between the TEPC and the Teledyne uDOS001 using the new method [ABSTRACT FROM AUTHOR]

Tissue equivalent proportional counter (TEPC) is used to measure the micro-dose spectrum of ionizing radiation. Through changing tissue-equivalent gas pressure, TEPC can simulate the case of radiation energy deposition in different sizes of human cells. Various dosimetric quantities can be obtained such as absorbed dose, radiation quality factor and micro-dose equivalent. Because TEPC simulated cell size is less than the range of ionizing radiation particles, TEPC can be used as linear energy transfer spectroscopy, which can identify different linear energy transfer particles in a mixed radiation field and play an important role in mixed neutron–photon radiation field monitoring and protection. A tissue equivalent proportional counter is designed and manufactured in this paper. Through the built of micro-dose detector signal testing platform, and the realization of measurement of micro-dose detector signal debugging and important parameters (stability, energy resolution, etc.) by α source method, micro-dose energy spectrum analysis and experimental measurements of Cf-252 source were ultimately achieved. Results show that the detector has good sealing performance and stability, with 12 h stability better than 2.7%. Based on all the above spectra, micro-dosing spectrum of Cf-252 source was experimentally obtained. [ABSTRACT FROM AUTHOR]

Single ventricle heart defects (SVDs) are congenital disorders that result in a variety of complications, including increased ventricular mechanical strain and mixing of oxygenated and deoxygenated blood, leading to heart failure without surgical intervention. Corrective surgery for SVDs are traditionally handled by the Fontan procedure, requiring a vascular conduit for completion. Although effective, current conduits are limited by their inability to aid in pumping blood into the pulmonary circulation. In this report, we propose an innovative and versatile design strategy for a tissue engineered pulsatile conduit (TEPC) to aid circulation through the pulmonary system by producing contractile force. Several design strategies were tested for production of a functional TEPC. Ultimately, we found that porcine extracellular matrix (ECM)-based engineered heart tissue (EHT) composed of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and primary cardiac fibroblasts (HCF) wrapped around decellularized human umbilical artery (HUA) made an efficacious basal TEPC. Importantly, the TEPCs showed effective electrical and mechanical function. Initial pressure readings from our TEPC in vitro (0.68 mmHg) displayed efficient electrical conductivity enabling them to follow electrical pacing up to a 2 Hz frequency. This work represents a proof of principle study for our current TEPC design strategy. Refinement and optimization of this promising TEPC design will lay the groundwork for testing the construct's therapeutic potential in the future. Together this work represents a progressive step toward developing an improved treatment for SVD patients. Single Ventricle Cardiac defects (SVD) are a form of congenital disorder with a morbid prognosis without surgical intervention. These patients are treated through the Fontan procedure which requires vascular conduits to complete. Fontan conduits have been traditionally made from stable or biodegradable materials with no pumping activity. Here, we propose a tissue engineered pulsatile conduit (TEPC) for use in Fontan circulation to alleviate excess strain in SVD patients. In contrast to previous strategies for making a pulsatile Fontan conduit, we employ a modular design strategy that allows for the optimization of each component individually to make a standalone tissue. This work sets the foundation for an in vitro , trainable human induced pluripotent stem cell based TEPC. Image, graphical abstract [ABSTRACT FROM AUTHOR]

During high altitude long haul flights pilots, cabin crew and passengers are exposed to enhanced level of radiation originating from cosmic ray showers (CRS), produced via the interaction of very high-energy (~GeV) primary protons with the air molecules in Earth's atmosphere. The CRS are composed of energetic particles of diverse species, i.e. neutrons, protons, electrons, muons, pions and photons. Furthermore, the magnitude of aircrew radiation exposure depends on flight altitude and duration, geographical location (latitude), geomagnetic conditions and solar activity (modulation) status. In 1990 the International Commission on Radiological Protection (ICRP) classified airline crewmembers as "radiation workers". A miniature passive microdosimeter (LiBe-14) based on LiF (TLD700) and Beryllium Oxide (BeO) thermoluminescence dosimeter chips emulating a large volume gas-filled Tissue Equivalent Proportional Counter (TEPC) was developed by one of the authors (BM). The LiBe-14 was deployed to assess the integrated ambient dose equivalent of two commercial pilots on long haul intercontinental flights during March–May 2017. The accumulated dose equivalents of 1st (38 y, Female, 148 total block hours) and 2nd (29 y, Male, 149 total block hours) pilots were evaluated to be 565 μSv ± 105 μSv and 738 μSv ± 137 μSv, respectively. The results agreed well within ±20% of simulated data evaluated using the well-known EPCARD (E uropean P rogram Package for the C alculation of A viation R oute D oses) aviation dosimetry code. The implementation of LiBe-14 Microdosimeter in routine long haul, high-altitude commercial flights for the estimation of dose equivalent, average LET and quality factor relevant to impinging cosmic radiation is recommended. • Microdosimeter (LiBe) based on LiF and BeO TLD. • Polystyrene phantom bombarded with 81- 231 MeV protons. • TLD cross calibration using a gas-filled TEPC. • Dose Equivalent, Average LET, Quality Factor. • LiBe-Microdosimeter used in aircrew dosimetry. [ABSTRACT FROM AUTHOR]

• Miniature Tissue Equivalent Proportional Counters can work without gas-flow. • The new sealed mini-TEPC gives reproducible results over a period of 4 months. • The new mini-TEPC can be used as a precise LET-monitor in proton therapy. • The new mini-TEPC measurements result in a reasonable RBE-assessment. • The mini-TEPC can be used for a comparative study of different radiotherapy centres. A new mini-TEPC with cylindrical sensitive volume of 0.9 mm in diameter and height, and with external diameter of 2.7 mm, has been developed to work without gas flow. With such a mini counter we have measured the physical quality of the 62 MeV therapeutic proton beam of CATANA (Catania, Italy). Measurements were performed at six precise positions along the Spread-Out Bragg Peak (SOBP): 1.4, 19.4, 24.6, 29.0, 29.7 and 30.8 mm, corresponding to positions of clinical relevance (entrance, proximal, central, and distal-edge of the SOBP) or of high lineal energy transfer (LET) increment (distal-dose drop off). Without refilling the microdosimeter with new gas, the measurements were repeated at the same positions 4 months later, in order to study the stability of the response in sealed-mode operation. From the microdosimetric spectra the frequency-mean lineal energy y - F and the dose-mean lineal energy y - D were derived and compared with average LET values calculated by means of Geant4 simulations. The comparison points out, in particular, a good agreement between microdosimetric y - D and the total dose-average L E T ¯ d , which is the average LET of the mixed radiation field, including the contribution by nuclear reactions. [ABSTRACT FROM AUTHOR]

Abstract In order to monitor the intense neutron and gamma radiation, multi-element tissue equivalent proportional counters (TEPC) based on the standard gas electron multiplier (GEM) and ceramic thick GEM (THGEM) foils were designed and respectively tested by implanted 55Fe and 241Am sources which would also be used as calibration sources. The performance testing of GEM-TEPC/THGEM-TEPC detectors at various parameters showed that the detectors could work well. The THGEM-TEPC was also used to measure the linear energy spectra in 241Am–Be and intense (108 ncm−2s−1) neutron radiation fields. The results displayed that THGEM-TEPC was available to do microdosimetric research or be a dosimeter in intense neutron/gamma field. [ABSTRACT FROM AUTHOR]

Abstract This paper discusses an instrument intercomparison performed in the high-energy field at the CERF facility at CERN between 2015 and 2017 (October 2015, May 2016, November 2016 and June 2017). Measurements were performed in several reference exposure locations with the CERN extended-range Bonner Sphere Spectrometer (BSS), a Berthold LB4611, the LINUS rem counter from CERN, the LUPIN rem counter from ELSE Nuclear, the FHT 762 Wide Energy Neutron Detection Instrument (WENDI-II) from Thermo Scientific, the LUDLUM MODEL 42–41 PRESCILA NEUTRON PROBE and two models of Tissue-equivalent proportional counters (TEPCs) from Far West Technologies. All results are compared with the latest FLUKA reference values from simulations performed in 2017. Highlights • The BSS , WENDI II, LINUS and LUPIN agree amongst them and with the FLUKA simulations within one sigma of uncertainty. • The LB6411 underestimates up to 35% as compared to FLUKA and the extended rem counters. • The PRESCILA overestimates the high-energy component and underestimate the evaporation part. Therefore, the PRESCILA overestimates the H*(10) on the CT and underestimates it on the IT. • Concerning the two TEPC , they agree within their range of uncertainty for all positions. The agreement with FLUKA is satisfactory on the CT/CS but the TEPCs show underestimation on the IT. [ABSTRACT FROM AUTHOR]

Radiation-induced bone diseases were frequently reported in radiotherapy patients. To study the diseases, microdosimeters were constructed with walls of A150-A150, A150-B100, B100-A150 and B100-B100 interfaces. Monte Carlo simulations of these microdosimeters were performed to determine the lineal energy spectra of an interface site at different depths in water for 230 MeV protons. Comparing these spectra with data of ICRU tissue and bone walls, better agreements were found at shallow depths for protons and delta-rays than deep depths for nuclear interactions. [ABSTRACT FROM AUTHOR]

The increase in the number of therapeutic proton and ion beam centres worldwide has prompted renewed interest in measuring and simulating microdosimetric spectra in order to help understand the complexity underlying the Relative Biological Effectiveness (RBE) of these treatment modalities. In this context we have studied the capability of the Geant4 toolkit to simulate microdosimetric spectra measured with a Tissue Equivalent Proportional Counter (TEPC) in a clinical carbon ion beam. The simulated spectra were compared with published experimental data obtained along the depth dose curve of a 194 MeV/u carbon beam at the GSI, Darmstadt (Gerlach et al., 2002). The initial beam energy and energy spread employed in the simulation were tuned to match the calculated and measured depth dose distributions. A good agreement was found at all depths after a shift of 4.025 mm was taken into account with agreement for the microdosimetric derived RBE values to within 0.4% and 11.9% for depths 40 and 66 mm in PMMA (Perspex). This work demonstrates that the Geant4 toolkit can accurately reproduce experimental microdosimetric data and can thus be used for independent calculation of lineal energy spectra from which RBE estimates can be derived using the equation of Pihet et al. (1990). The work highlights the difficulty in using experimental work to benchmark Monte Carlo simulations and the need for detailed descriptions of experimental setups used. [ABSTRACT FROM AUTHOR]

Knowledge about the single-event energy deposition in a subcellular biological target, e.g. cell nucleus, is required in order to understand the radiation action and the biological effectiveness of ionizing radiation. This energy deposition can be measured using a tissue equivalent proportional counter (TEPC). Such measurements are particularly useful to find the microdosimetric spectra for mixed radiation fields comprising different radiation types and energies. In the present work, several mixed radiation fields were generated by irradiating a mini TEPC, containing a small plug inserted into the hole on the counter wall, with reactor neutrons. The plug, made of A150, boron, nitrogen, lithium or cadmium mixture, was designed to generate different ionizing particles under the neutron irradiation. The measured spectra separated the contributions to the absorbed dose from electrons (photons), protons (neutrons) and heavy ions. The lineal energy spectra demonstrated that three distinct regions of lineal energy y , were identified, i.e. the region from heavy ions at y >100 keV/µm, the region for recoil protons at 10< y <100 keV/µm, and the region due to electrons at y <10 keV/µm. In all measurements, the proton edge and the electron edge were used as marking points to calibrate the lineal energies. The relative magnitudes of the measured spectra in each y region depended on the yields and stopping powers of nuclear reaction products. For instance, lineal energy peaks were identified at y >100 keV/µm due to the 10 B (n, α) 7 Li reaction. If one substitutes the plug material by a radionuclide, microdosimetry spectra could be measured for internal dosimetry applications. [ABSTRACT FROM AUTHOR]

Neutron spectrometry measurements with an extended-range Bonner Sphere Spectrometer (BSS), as well as neutron H*(10) measurements using an extended-range rem meter WENDI-2, a conventional rem meter LB 6411 and a tissue-equivalent proportional counter, were performed inside and around the Fixed-Beam Treatment Room at the proton therapy facility of Essen, in Germany. The WENDI-2 stood out as the easiest detector for making accurate neutron H*(10) measurements, since its direct measurements were equivalent to the H*(10) rates obtained with the BSS. The measurements were also compared to simulation results obtained with MCNPX 2.7.0 using two different selections of physics models for the hadron interactions above 150 MeV: the Bertini & Dresner models and the CEM03 model. For neutron H*(10) rates outside the treatment room, factors of 1.6–1.8 were obtained between the results of the two simulations, the Bertini & Dresner models yielding the largest values in all positions. The comparison of the simulation results with the WENDI-2 and BSS measurements for positions inside the treatment room showed that the Bertini & Dresner models reproduce the global neutron production in the water phantom relatively well, whereas the CEM03 model underestimates it by a factor of ∼1.3. At the most-forward angle, however, the Bertini model (unlike the CEM03 model) seemed to overestimate the production of neutrons with energies above 100 MeV. Outside the shielding, the simulated H*(10) overestimated the WENDI-2 measurements by factors of 2–3 with the Bertini & Dresner models, and 1.1–1.7 with the CEM03 model. Both simulations were thus conservative with respect to the neutron fluxes transmitted through the concrete walls. This conservative behaviour is probably caused by a combination of several uncertainties, including for instance uncertainties on the proton and neutron interaction cross-sections and uncertainties on the concrete composition and density. [ABSTRACT FROM AUTHOR]

Purpose To measure the environmental doses from stray neutrons in the vicinity of a solid slab phantom as a function of beam energy, field size and modulation width, using the proton pencil beam scanning (PBS) technique. Method Measurements were carried out using two extended range WENDI-II rem-counters and three tissue equivalent proportional counters. Detectors were suitably placed at different distances around the RW3 slab phantom. Beam irradiation parameters were varied to cover the clinical ranges of proton beam energies (100–220 MeV), field sizes ((2 × 2)–(20 × 20) cm 2 ) and modulation widths (0–15 cm). Results For pristine proton peak irradiations, large variations of neutron H ∗ (10)/ D were observed with changes in beam energy and field size, while these were less dependent on modulation widths. H ∗ (10)/ D for pristine proton pencil beams varied between 0.04 μSv Gy −1 at beam energy 100 MeV and a (2 × 2) cm 2 field at 2.25 m distance and 90° angle with respect to the beam axis, and 72.3 μSv Gy −1 at beam energy 200 MeV and a (20 × 20) cm 2 field at 1 m distance along the beam axis. Conclusions The obtained results will be useful in benchmarking Monte Carlo calculations of proton radiotherapy in PBS mode and in estimating the exposure to stray radiation of the patient. Such estimates may be facilitated by the obtained best-fitted simple analytical formulae relating the stray neutron doses at points of interest with beam irradiation parameters. [ABSTRACT FROM AUTHOR]

Traditionally experimental microdosimetry has employed low pressure single cavity spherical Tissue Equivalent Proportional Counters (TEPCs). Multi-Element Tissue Equivalent Proportional Counters (METEPCs) with numerous cylindrical cavities have been constructed in order to increase sensitivity per unit volume; however existing METEPC designs are prohibitively complex and sensitive to motion and audible noise. This work proposes a novel hemispherical element with a wire-less anode ball as a solution to these issues. The gas gain characteristics of this hemispherical METEPC element were analyzed first for a single hemispherical TEPC to evaluate performance relative to current cylindrical and spherical counter designs that have been demonstrated experimentally to perform very well. This gain analysis evaluated relative avalanche size and the uniformity in maximum gain for electrons originating throughout the gas cavities of each of the three counters. Radial gas gain distributions for each counter were determined using both theoretical potential distributions as well as analytical equipotential distributions generated with ANSYS Maxwell (V. 14.0) to solve the Townsend equation. It was found that the hemispherical counter exhibits completely uniform gas gain for electrons approaching the anode from all directions and its avalanche region occupies only 3.5×10 −3 % of the entire gas cavity volume, whereas in the cylindrical and spherical counters the avalanche occupies 0.6% and 0.12% of the total respective gas cavity volumes. These analytical gas gain results are promising, suggesting that the hemisphere should exhibit uniform signal amplification throughout the gas cavity and if the recommended follow-up experimental work demonstrates the hemispherical counter works as anticipated it will be ready to be incorporated into an METEPC design. [ABSTRACT FROM AUTHOR]

A new miniaturized Tissue Equivalent Proportional Counter (mini‒TEPC) with cylindrical sensitive volume of 1.0 mm in diameter and height, and with external diameter of 1.53 cm, has been developed to work without gas flow. With this mini counter we have measured the radiation quality of the 148 MeV energy-modulated proton beam at the radiobiological research line of the Trento Proton Therapy Centre. The irradiation field had a diameter of about 6 cm, a modulation width of 2.5 cm and a range of about 13.5 cm. At four specific depths, the response function of the new microdosimeter has also been compared to that of a commercial spherical microdosimeter, the LET-1/2" Spherical TEPC produced by Far West Technology. Afterwards, measurements were performed with the mini‒TEPC at nine precise positions across the Spread-Out Bragg Peak (SOBP). From the microdosimetric spectra the frequency and the dose‒mean lineal energy values, y ‾ F and y ‾ D , were derived for both detectors. Afterwards, microdosimetric assessment of Relative Biological Effectiveness ( R B E μ) has been performed by weighting the dose distribution of the lineal energy, d(y), with the Loncol's biological weighting function r(y). R B E μ has been used to calculate the R B E μ D at different dose levels D. In the distal fall-off region the R B E μ D (d) increases significantly, up to a factor 3. Finally, the R B E μ D -weighted dose was calculated and compared to that obtained with a fixed RBE = 1.1. The use of a variable RBE to weight the physical dose leads to a biological range extension evaluated at R80 of about 2.0 mm, with respect to the R80 obtained with a fixed RBE = 1.1. The use of a mini‒TEPC in proton therapy has been so far limited to 60 MeV proton beams, used for the treatment of ocular melanoma. This is the first time that a mini-TEPC was used with an higher energy proton beam of 148 MeV, and the spectra measured with the mini-TEPC were compared to those measured with the commercial FWT LET1/2 counter for the first time. These new results corroborate the usability of mini-TEPCs in proton therapy. • Mini-TEPC for radiation quality characterization. • Microdosimetry of a 148 MeV proton beam. • RBE assessment in proton therapy through microdosimetry. • RBE increases at the distal edge of proton beams. [ABSTRACT FROM AUTHOR]

Tissue equivalent proportional counters (TEPCs) can be used as radiation monitors in different radiation environments, including on board of a spacecraft or aircraft. Usually, the gas density of the counter is set to simulate site sizes of 1 μm or 2 μm. However, especially for sealed counters which should be operative for long time without being refilled, the gas density inside the counter could change significantly. The immediate consequence of density variations is a gas gain shift. This in turn is not a serious problem, because the gas gain can be measured and corrected by increasing the bias voltage. A more critical consequence of an increase of the density is that the shape of the microdosimetric spectrum changes, affecting the response of the detector. Consequently, this limits the reliability of sealed TEPC over time, especially because the gas pressure is not directly monitored. Therefore, the aim of this study is to propose an experimental procedure to estimate the TEPC sensitive-site size by performing two independent measurements, one in a gamma radiation field and the other one in a neutron field. The results show that it is possible to assess the site size of sealed TEPCs with an accuracy of 5%. [ABSTRACT FROM AUTHOR]

Personnel working in the environment of nuclear reactors, fuel reprocessing facilities, high energy accelerators get exposed to a mixed radiation field of electrons, photons, and neutrons with a wide range of energy and fluence. Performance evaluations of the passive personnel dosimeters in these mixed radiation environments require knowledge of the external dose contributed by different types of radiations having variation in their energy, etc. Tissue Equivalent Proportional Counters (TEPC), sensitive to a wide range of particles and energy (Linear Energy Transfer (LET) ∼ 0–1500 keV μm−1), is one of the standard reference detectors which can be used for the characterization of mixed radiation fields. In the present work, HAWK TEPC was used to evaluate different microdosimetric parameters such as dose mean lineal energy (ӯ D), average quality factor (Ǭ), the contribution of gamma and neutron dose equivalents for the characterizations of the radiation fields inside in a nuclear research reactor hall, fuel reprocessing facility, D-D neutron beam facility, radionuclide source based neutron calibration facilities, etc. Measured results were compared with Monte Carlo simulated values using radiation transport code PHITS. TEPC measurement shows that the radiation work field around nuclear reactor facility is dominated by gamma rays with approximate ӯ D and Ǭ of ∼42 keV μm−1 and ∼2.3, respectively. Whereas ӯ D and Ǭ values for neutron dominated locations in fuel reprocessing facility are 82 keV μm−1 and 8.2, respectively. Ǭ values near thermal neutron beam line in research reactor are close to 1 due to (n, γ) reaction. For 2.54 MeV mono-energetic D-D neutron beam, measured and calculated dose mean lineal energies (ӯ D) are 52.5 keV μm−1 and 59.6 keV μm−1, respectively, whereas corresponding Ǭ values are 11.23 and 13.01. Obtained values can be utilized to correlate the neutron and gamma dose equivalents measured by passive detectors used for personnel monitoring program to enhance confidence in the dosimetry. • TEPC based measurement of dose mean lineal energy and radiation quality factor at mixed radiation environments. • Lineal energy spectra analysis at nuclear reactor, fuel reprocessing facility and D-D neutron generator environment. • PHITS based Monte Carlo simulations for different microdosimetric parameters. • Comparison of TEPC and Monte Carlo based results for radionuclide based neutron sources. [ABSTRACT FROM AUTHOR]

The Active Tissue Equivalent Dosimeter (ATED) is a low-cost, easy-to-use and compact tissue equivalent proportional counter designed for use aboard spacecraft, satellites, aircraft, unmanned aerial vehicles and high-altitude balloons. ATED was rigorously tested at particle accelerator facilities utilizing heavy ions of charge and energy similar to Galactic Cosmic Rays (GCRs). Upon completion of the ground-based testing and calibration, the ATED was operated aboard the International Space Station (ISS) during July–August of 2018. ATED measurements from the ISS were then analyzed in terms of time, latitude, longitude, and altitude in order to correlate with the radiation fields in the ISS orbit. When ATED measurements were correlated with orbital position, elevated absorbed dose rates due to the South Atlantic Anomaly (SAA) were clearly evident. ATED measurements were also separated based on their orbital location into three different regions. The results from the July–August 2018 flight show that ATED functioned as designed while onboard the ISS. The hypothesis that lineal energy and linear energy transfer can be used interchangeably with measurements by a TEPC in Low Earth Orbit (LEO) was tested by ATED measurements. Lastly, a direct comparison was made between linear energy transfer (LET) converted from lineal energy spectra from a spherical TEPC in LEO and model-calculated LET values. Such a comparison is highly challenging with the TEPCs with cylindrical geometry previously used in space. [ABSTRACT FROM AUTHOR]

A Geant4 model of a tissue-equivalent proportional counter (TEPC) has been developed in which the calculated output spectrum exhibits unparalleled agreement with experiment for monoenergetic neutron fields at several energies below 20 MeV. The model uses the standard release of the Geant4 9.6 p2 code, but with a non-standard neutron cross section file as provided by Mendoza et al., and with the environment variable options recommended by the same authors. This configuration was found to produce significant improvements in the alpha-dominated region of the calculated response. In this paper, these improvements are presented, and the post-processing required to convert deposited energy into the number of ion pairs (which is the quantity actually measured experimentally) is discussed. [ABSTRACT FROM AUTHOR]

Cosmic ray neutrons are produced by the interaction of primary cosmic rays with the air molecules present in the atmosphere. At the ground level, these secondary neutrons are one of the important contributors of natural cosmic ray radiation background dose. With two major peaks around 1 MeV and 100 MeV, the neutron energies can extend up to 10 GeV. At the ground level, considerable presence of thermal neutrons can also be observed due to collisions and moderation of fast neutrons with the soil and other surrounding materials. A study on the evaluation of cosmic ray neutron spectra, and the resulting ambient dose equivalents was carried out at High Altitude Research Laboratory, Gulmarg, India (altitude 2650 m, N34.0484°, E74.3805°) considering the enhanced contribution of cosmic ray background in the region. Extended energy Bonner Sphere Spectrometer (BSS) was used for the continuous measurement of cosmic ray neutrons during the period of October 2018 to June 2019. Neutron spectra and ambient dose equivalents were unfolded from the BSS counts with the Monte Carlo generated response matrix and the FRUIT unfolding code. Along with Bonner sphere spectrometer, Tissue Equivalent Proportional Counter (TEPC) was also used for a limited period for independent measurement of cosmic ray dose equivalents and Linear Energy Transfer (LET) distribution. For comparison, neutron spectra and dose equivalent rates were also calculated using Monte Carlo code FLUKA and EXPACS software program. The ambient dose equivalent rates were found to vary in the range of 24–34 nSv. h−1 during the entire observation period of 9 months. No considerable seasonal variations were observed during the course of the study. Dose equivalent rates, estimated by the TEPC were slightly higher than the neutron dose equivalent rates measured by BSS. Experimentally measured values match reasonably well with theoretically simulated results. • Neutron spectra of cosmic rays. • Ambient dose equivalent H*(10). • Microdosimetric spectra. • Response matrix calculation using Monte Carlo code. • Unfolding of neutron spectra. [ABSTRACT FROM AUTHOR]

To study the agreement between proton microdosimetric distributions measured with a silicon-based cylindrical microdosimeter and a previously published analytical microdosimetric model based on Geant4-DNA in-water Monte Carlo simulations for low energy proton beams. Distributions for lineal energy (y) are measured for four proton monoenergetic beams with nominal energies from 2.0 MeV to 4.5 MeV, with a tissue equivalent proportional counter (TEPC) and a silicon-based microdosimeter. The actual energy for protons traversing the silicon-based microdosimeter is simulated with SRIM. Monoenergetic beams with these energies are simulated with Geant4-DNA code by simulating a water cylinder site of dimensions equal to those of the microdosimeter. The microdosimeter response is calibrated by using the distribution peaks obtained from the TEPC. Analytical calculations for y ‾ F and y ‾ D using our methodology based on spherical sites are also performed choosing the equivalent sphere to be checked against experimental results. Distributions for y at silicon are converted into tissue equivalent and compared to the Geant4-DNA simulated, yielding maximum deviations of 1.03% for y ‾ F and 1.17% for y ‾ D. Our analytical method generates maximum deviations of 1.29% and 3.33%, respectively, with respect to experimental results. Simulations in Geant4-DNA with ideal cylindrical sites in liquid water produce similar results to the measurements in an actual silicon-based cylindrical microdosimeter properly calibrated. The found agreement suggests the possibility to experimentally verify the calculated clinical y ‾ D with our analytical method. • Validation of analytical microdosimetric models for protons of low energy. • Silicon-based microdosimeter is calibrated and employed for experimental data. • Distributions and averages of lineal energy are compared. • We found agreement among experiments, Geant4-DNA and analytical results. [ABSTRACT FROM AUTHOR]

Microdosimetry is an important tool for assessing energy deposition distributions from ionizing radiation at cellular and cellular nucleus scales. It has served as an input parameter for multiple common mathematical models, including evaluation of relative biological effectiveness (RBE) of carbon ion therapy. The most common detector used for microdosimetry is the tissue-equivalent proportional counter (TEPC). Although it is widely applied, TEPC has various inherent uncertainties. Therefore, this work quantified the magnitude of TEPC measurement uncertainties and their impact on RBE estimates for therapeutic carbon beams. Microdosimetric spectra and frequency-, dose-, and saturation-corrected dose-mean lineal energy (****) were calculated using the Monte Carlo toolkit Geant4 for five monoenergetic and three spread-out Bragg peak carbon beams in water at every millimeter along the central beam axis. We simulated the following influences on these spectra from eight sources of uncertainty: wall effects, pulse pile-up, electronics, gas pressure, W-value, gain instability, low energy cut-off, and counting statistics. Statistic uncertainty was quantified as the standard deviation of perturbed values for each source. Bias was quantified as the difference between default lineal energy values and the mean of perturbed values for each systematic source. Uncertainties were propagated to RBE using the modified microdosimetric kinetic model (MKM). Variance introduced by statistic sources iny¯Fandy¯Daveraged 3.8% and 3.4%, respectively, and 1.5% iny*across beam depths and energies. Bias averaged 6.2% and 7.3% iny¯Fandy¯D,and 4.8% iny*.These uncertainties corresponded to 1.2 ± 0.9% on average in RBE MKM . The largest contributors to variance and bias were pulse pile-up and wall effects. This study established an error budget for microdosimetric carbon measurements by quantifying uncertainty inherent to TEPC measurements. It is necessary to understand how robust the measurement of RBE model input parameters are against this uncertainty in order to verify clinical model implementation., (© 2021 Institute of Physics and Engineering in Medicine.)

Microdosimetric parameters measured by a TEPC have been studied in the mixed radiation fields generated by the two D-T neutron generators developed at BARC and IGCAR facilities of DAE, India. These two generators differ in their sizes and designs. The present study reveals that the radiation fields by these two generators are significantly different. In the case of compact design (IGCAR generator) due to the significant contribution of bremsstrahlung photons in the total radiation field, the frequency and dose mean lineal energy, average quality factors are considerably less (factors of 3 to 6) than the BARC D-T generator. The study also reveals that the photon contribution to the total dose equivalent can be as high as 30% for compact D-T generator. • Measurement of microdosimetric parameters of neutrons produced by D-T generator using TEPC. • Average quality factor of the mixed radiation field of the D-T generator. • Microdosimetric spectra of high energy neutrons. [ABSTRACT FROM AUTHOR]

Tissue equivalent proportional counter (TEPC) model HAWK FWAD-3 was used for the evaluation of absorbed dose, dose equivalent rate (Ḣ TEPC) and microdosimetric spectra measured (i) in the mixed radiation fields formed mainly by cosmic rays onboard aircraft during the flights between Mumbai and the Indian station Bharati (Progress air base), two polar flights at Antarctica, and (ii)ground level environmental radiation field at locations situated in three continents, namely Antarctica, Africa and Asia with different latitudes. The study also includes evaluation of absorbed dose rate, dose equivalent rate of cosmic rays and terrestrial radiation using active detectors namely RADEYE-G and BERTHOLD Rem counter. An effort was made to compare the measured dose equivalent rate by TEPC for the commercial flight routes to Antarctica with the values calculated by the software code EPCARD and a good agreement was observed. The 35th expedition to Bharati, Antarctica showed higher values of dose equivalent at the pole (Larsemann Hills region, 69°24′37.60″S, 76°11′01.70″E) than the world average for an evaluation period of six months during summer. • TEPC used for the measurement of absorbed dose, Ḣ TEPC and microdosimetric spectra for the flight routes. • Measurement of absorbed dose, Ḣ TEPC and microdosimetric spectra at locations of three continents including Antarctica. • Analysis of low and high LET components of cosmic ray to absorbed dose at different altitudes. • Comparison of the measured flight route doses were made with the calculated values by the software code EPCARD. [ABSTRACT FROM AUTHOR]