Automatic measurements with the Pille-ISS thermoluminescent dosimeter system on board the International Space Station (2003-2021).

The health risk of staying in space is a well-known fact, and the radiation doses to the astronauts must be monitored. The Pille-ISS thermoluminescent dosimeter system is present on the International Space Station (ISS) since 2003. We present an analysis of 60000 data points over 19 years from the 90 min automatic measurements and show a 4-day-long segment of 15 min measurements. In the case of the 15 min we show that the mapping of the radiation environment for the orbit of the ISS is possible with the Pille system. From our results the dose rates inside the South Atlantic Anomaly (SAA) are at least 1 magnitude higher than outside. From the 90 min data, we select orbits passing through the SAA. A statistical correlation in the SAA between the ISS altitude and monthly mean dose rate is presented with the Spearman correlation value of ρSAA=0.56. The dose rate and the sunspot number show strong inverse Pearson correlation (R2=-0.90) at a given altitude.

Off-the-shelf thermoluminescent silica glass media for use in medical diagnostic dosimetry applications.

In respect of radiation exposure assessments, thermoluminescent dosimeters (TLD) represent a notable and important subset of passive detector technology, gaining widespread use over a period of many decades, not least for medical applications. TLDs are available in a range of physical and chemical forms, in particular the popularity of phosphor-based commercial products arising from features that include availability down to low mm dimensions, soft-tissue equivalence in some cases, and relatively low TL fading. Novel doped silica glass TL material fabricated as fibres also offer favourable responses, recent developments in co-doping leading to their ability to also provide for diagnostic radiology applications, adding to the attractive features of being impervious to water, of good sensitivity, and generally offering wide dynamic range. Thus said, doping and fibre fabrication involve relatively high costs. Accordingly, herein exploratory investigations are made of the cost-effective colourless silica-based glass medium from which marbles are made, reduced into chip form for ease of application, examining sensitivity to dose. In particular, the study focuses on the computerised tomography clinical application regime, 80- to 140 kVp, with excellent response being shown for doses within the range 2- to 50 mGy.

Photonic crystal fibre as a potential medium for radiotherapy dosimetry.

Present study concerns the key thermoluminescence (TL) properties of photonic crystal fibres (PCFs), seeking development of alternatively structured TL materials that are able to offer a advantages over existing passive dosimeters. In terms of their internal structure and light guiding properties the PCFs, collapsed and structured, differ significantly from that of conventional optical fibres. To investigate the dosimetric parameters of the PCFs use was made of a linear accelerator producing a 6 MV photon beam, delivering doses ranging from 0.5 Gy to 8 Gy. The parameters studied included TL response, linearity index, glow curves, relative sensitivity and TL signal fading, the results being compared against those obtained using TLD-100 chips. At 4 Gy photon dose the Ge-doped collapsed PCFs were found to provide a response 27 × that of structured PCF, also giving a TL yield similar to that of standard TLD-100 chips. Over post-irradiation periods of 15 and 30 days collapsed PCF TL signal fading were 8% and 17% respectively, with corresponding values of 37% and 64% for the structured PCF. Trapping parameters including the order of kinetics (b), activation energy (E) and frequency factor (s-1) were assessed with Chen's peak shape method. Lifetime of trapping centre was found to be (2.36 E+03) s and (9.03 E +01) s regarding the collapsed and structured PCF respectively with 6 Gy of photon beam. For the Ge-doped collapsed PCF, the high TL yield, sensitivity and low fading provide the basis of a highly promising system of TLD for radiotherapy applications.

Ambient and personnel occupational dose assessment in a Hospital's PET/CT center.

This study used thermoluminescent dosimeters (TLDs) to measure cumulative radiation doses in a PET/CT center. It covered 18 areas and four personnel groups. Because the isolated lead shielding separated the patients from the nurses, wearing protective clothing when injecting radiopharmaceuticals was unnecessary. Fingertip doses of the dispensing and nurse groups were below the occupational limit. Current radiopharmaceutical transportation and injection operations in this PET/CT center provide considerable radiation protection to medical personnel.

Low-cost commercial borosilicate glass slides for passive radiation dosimetry.

For x- and gamma- irradiations delivering entrance doses from 2- up to 1000 Gy to commercial 1.0 mm thick borosilicate glass microscope slides, study has been made of their thermoluminescence yield. With an effective atomic number of 10.6 (approximating bone equivalence), photon energy dependency is apparent in the low x-ray energy range, with interplay between the photoelectric effect and attenuation. As an example, over the examined dose range, at 120 kVp the photon sensitivity has been found to be some 5× that of 60Co gamma irradiations, also with repeatability to within ~1%. The glow-curves, taking the form of a single prominent broad peak, have been deconvolved yielding at best fit a total of five peaks, the associated activation energies and frequency factors also being obtained. The results indicate borosilicate glass slides to offer promising performance as a low-cost passive radiation dosimeter, with utility for both radiotherapy and industrial applications.

A Comparison of Readings from Thermoluminescent Dosimeter Ring Badges Worn in Different Positions.

Our purpose was to evaluate whether the position of a thermoluminescent dosimeter (TLD) crystal results in different exposure readings. Methods: Nine subjects wore 2 TLD badges (one facing inward, toward the palm, and one facing outward) for 2 mo. Both TLDs were worn on the middle finger of the dominant hand, with the inward-facing TLD placed at the bottom and the outward-facing TLD at the top. At the end of the first month, these TLDs were replaced with new ones for another month. Combined results from the badges for the 2 mo were recorded in millisieverts. A paired t test with 2-sample means was performed to compare the 2 positions in general nuclear medicine and PET/CT subjects, with an α of 0.05. Results: For all subjects and for the general nuclear medicine and PET/CT groups, mean exposure was greater for the inward-facing TLD. Conclusion: For a TLD worn on the dominant hand, extremity-exposure readings are maximized when the TLD faces inward.

Microscope cover-slip glass for TLD applications.

As a result of the various evolving needs, thermoluminescence dosimetry is constantly under development, with applications intended in environmental and personal radiation monitoring through to the sensing of radiotherapy and radiation processing doses. In radiotherapy dosimetry challenges include small-field profile evaluation, encompassing the fine beams of radiosurgery, evaluations confronting the steep dose gradients of electronic brachytherapy and the high dose rates of FLASH radiotherapy. Current work concerns the thermoluminescent dosimetric properties of commercial low-cost borosilicate glass in the form of thin (sub-mm to a few mm) plates, use being made of microscope cover-slips irradiated using clinical external-beam radiotherapy facilities as well as through use of 60Co gamma irradiators. In using megavoltage photons and MeV electrons, characterization of the dosimetric response has been made for cover-slips of thicknesses up to 4 mm. Reproducibility to within +/5% has been obtained. In particular, for doses up to 10 Gy, the borosilicate cover-slips have been demonstrated to have considerable potential for use in high spatial resolution radiotherapy dosimetry, down to 0.13 mm in present work, with a coefficient of determination in respect of linearity of >0.99 for the thinner cover-slips. Results are also presented for 0.13- and 1.00-mm thick cover slips irradiated to 60Co gamma-ray doses, initially in the range 5- to 25 Gy, subsequently extended to 5 kGy-25 kGy, again providing linear response.

A practical method for the reuse of nanoDot OSLDs and predicting sensitivities up to at least 7000 cGy.

PURPOSE: Optically stimulated luminescence dosimeter (OSLDs) are often used to make in vivo dose measurements. Most users calibrate the OSLDs using the software provided by the vendor which typically is intended for doses up to about 300 cGy with an uncertainty of ±5.5%. OSLDs that reach that dose are then discarded, and new ones are purchased and calibrated. A method has been developed for reusing OSLDs and predicting dose sensitivity up to at least 7000 cGy. MATERIALS AND METHODS: The nanoDot OSLDs used in this study were routinely used to do in vivo measurements for TBI patients. Instead of using the calibration program provided by the vendor, each nanoDot was bleached to about 100 counts (~0.1 cGy), then calibrated with 50 cGy to produce a sensitivity specific to each nanoDot prior to the patient measurement. NanoDots were read in the hardware mode and the sensitivity factor was applied manually to subsequent patient in-vivo TBI measurements. This was followed by bleaching prior to the next use. The changes of nanoDot sensitivity relative to accumulated dose were analyzed among nine nanoDots. In addition, a method to predict a nanoDot's sensitivity was investigated which aims to reduce the number of sensitivity calibrations while retaining dosimetric accuracy. RESULTS: Individual per-use nanodot calibrations were performed up to 7000 cGy for 37 clinical TBI patients. Among the nine nanoDots analyzed in this paper, the sensitivity vs accumulated dose decreased linearly up to about 3000 cGy, with linear fitting curve R2 values above 0.93. After 3000 cGy of accumulated dose, the sensitivity started to plateau and tended to increase by 6000 cGy, with 2nd order polynomial curve R2 values above 0.94. With this finding, an efficient and accurate method to predict nanoDots' sensitivities was developed. With the method applied to the nine OSLDs, a total of 127 sensitivities were predicted and retrospectively compared with measured sensitivities. The predicted sensitivities agreed with measured sensitivities within ±4.0% with an average of -0.8%. CONCLUSIONS: This study is the first to demonstrate the reuse of nanoDot OSLDs on numerous patients with accumulated dose up to 7000 cGy. Our nanoDot re-usage methodology is accurate, cost-saving and feasible. A time-saving method is also provided that allows a user to reuse a nanoDot with sensitivities predicted with better accuracy than the 5.5% value provided by the conventional batch calibration method.

Absorbed dose measurements from a 90Y radionuclide liquid solution using LiF:Mg,Cu,P thermoluminescent dosimeters.

In the last few years there has been an increasing interest in the measurement of the absorbed dose from radionuclides, with special attention devoted to molecular radiotherapy treatments. In particular, the determination of the absorbed dose from beta emitting radionuclides in liquid solution poses a number of issues when dose measurements are performed using thermoluminescent dosimeters (TLD). Finite volume effect, i.e. the exclusion of radioactivity from the volume occupied by the TLD is one of these. Furthermore, TLDs need to be encapsulated into some kind of waterproof envelope that unavoidably contributes to beta particle attenuation during the measurement. The purpose of this study is twofold: I) to measure the absorbed dose to water, Dw, using LiF:Mg,Cu,P chips inside a PMMA cylindrical phantom filled with a homogenous 90YCl3 aqueous solution II) to assess the uncertainty budget related to Dw measurements. To this purpose, six cylindrical PMMA phantoms were manufactured at ENEA. Each phantom can host a waterproof PMMA stick containing 3 TLD chips encapsulated by a polystyrene envelope. The cylindrical phantoms were manufactured so that the radioactive liquid environment surrounds the whole stick. Finally, Dw measurements were compared with Monte Carlo (MC) calculations. The measurement of absorbed dose to water from 90YCl3 radionuclide solution using LiF:Mg,Cu,P TLDs turned out to be a viable technique, provided that all necessary correction factors are applied. Using this method, a relative combined standard uncertainty in the range 3.1-3.7% was obtained on each Dw measurement. The major source of uncertainty was shown to be TLDs calibration, with associated uncertainties in the range 0.7-2.2%. Comparison of measured and MC-calculated absorbed dose per emitted beta particle provided good results, with the two quantities being in the ratio 1.08.

Modeling the radiation-induced cell death in a therapeutic proton beam using thermoluminescent detectors and radiation transport simulations.

Changes in the relative biological effectiveness (RBE) of the radiation-induced cell killing of human salivary glands (HSG) were assessed along the Bragg peak of a 60 MeV clinical proton beam by means of coupling biophysical models with the results of Monte Carlo radiation transport simulations and experimental measurements with luminescent detectors. The fluence- and dose-mean unrestricted proton LET were determined along the Bragg peak using a recently developed methodology based on the combination of the response of 7LiF:Mg,Ti (MTS-7) and 7LiF:Mg,Cu,P (MCP-7) thermoluminescent detectors. The experimentally assessed LET values were compared with the results of radiation transport simulations using the Monte Carlo code PHITS, showing a good agreement. The cell survival probabilities and RBE were then calculated using the linear-quadratic model with the linear term derived using a phenomenological LET-based model (Carabe A et al 2012 Phys. Med. Biol. 57 1159) in combination with the experimentally-assessed or PHITS-simulated dose mean proton LET values. To the same aim, PHITS simulated microdosimetric spectra were used as input to the modified microdosimetric kinetic model (modified MKM, (Kase et al 2006 Radiat. Res. 166 629-38)). The RBE values calculated with the three aforementioned approaches were compared and found to be in very good agreement between each other, proving that by using dedicated pairs of thermoluminescent detectors it is possible to determine ionization density quantities of therapeutic proton beams which can be applied to predict the local value of the RBE.

Technical Note: Robust individual thermoluminescence dosimeter tracking using optical fingerprinting.

PURPOSE: The thermoluminescence dosimeter (TLD) has desirable features including low cost, reusability, small size, and relatively low energy dependence. However, the commonly available poly-crystal TLDs (e.g., TLD-100) exhibit high interdetector variability that requires individual calibration for high detection accuracy. To improve individual TLD tracking robustness, we developed an optical fingerprinting method to identify the TLD-100 chips. METHODS: Seven hundred and fifty-two images were initially captured using a digital microscope camera to build a feature library for both facets of 376 TLD-100 chips. A median intensity thresholding method was used to segment images into foreground and background. The affine transformation was used to register the segmented images to the same position. The fingerprint of each image was calculated from its registered image. All fingerprints were then recorded in an Elasticsearch® search database. The TLD fingerprint match was tested three times when the library was established and repeated once 20 months later. All chips were irradiated at 0, 1, 4, and 8 Gy on a calibrated clinical MV linac to establish the individual calibration curve. RESULTS: The true positive rate of identifying TLDs based on their optical fingerprints was 100% at initialization of the inventory. After 20 months and multiple deployments for characterization, calibration, and dose measurement, the true positive match rate dropped to 99% with zero false-positive matches. The TLDs exhibited high self-consistency in the dose-response test with R2 between 0.988 and 1 with linear regression. CONCLUSIONS: The TLD-100 chips surface textures are unique and sufficient to support accurate identification based on the optical fingerprinting. This method provides inexpensive and robust management of the TLDs for individual calibration and dosimetry.

Effect of Teflon Transmittance on Sensitivity of Thermoluminescence Dosimeter Cards.

Thermoluminescence dosimeter cards purchased by the US Navy in recent years have different radiation sensitivities, e.g., they exhibit a different amount of light per dose unit. Presented tests indicate that the optical transparency of the Teflon encapsulation is partially responsible for the significant variation of the DT-702/PD radiation sensitivity. It was confirmed also that the Teflon transparency is in fact a primary cause of the radiation sensitivity increase in the most recently produced dosimetric cards. This conclusion is based on the correlation found between the calibrated radiation sensitivity of the dosimeter card element and the optical transparency of its Teflon encapsulation. The transparency measurements were performed at the wavelength of 400 nm within a 10 nm spectral interval effectively covering the spectral range of the thermoluminescence. It is anticipated that the experimentally determined correlation will help to approve the acceptance of new thermoluminescence dosimeter cards in the Naval Dosimetry Center inventory as well as improve the production process.

Dosimetry of ruthenium-106 ophthalmic applicators with thin layer thermoluminescence dosimeters - Clinical quality control.

Ruthenium-106 ophthalmic applicators have proven to be effective when using beta emitters in brachytherapy. For dose calculations , typically, the dosimetric reference data given by the manufacturer are used. An additional check of the applicators is usually not provided. However, the medical physicist is responsible for correct dosimetry in the clinic; therefore dosimetric verification is desirable. Despite the fact that the use of beta-ray emitting sealed brachytherapy sources is a safe treatment method, errors can occur (Kaulich et al., 2004). Hence, a method for absolute dose measurements based on the use of thin layer MCP-N-thermoluminescence detectors (TLD Poland, Krakow, Poland) is described in this study. A custom-made polymethyl methacrylate (PMMA)- based phantom was developed for this study. The surface of the phantom was designed to fit with spherical shells of ruthenium-106 ophthalmic applicators (e.g. applicator type CCA, CCB and CIA by Eckert & Ziegler BEBIG GmbH, Berlin, Germany) studied in this work. To verify the reference data from the source certificates, absolute point dose values were measured at different phantom depths with the thermoluminescence detectors and compared to the certificate values. Calibrations of the thermoluminescence detectors were performed in a water phantom with a 6 MV CLINAC (Artiste, Siemens Medical, Erlangen, Germany) before. A comparison with scintillator measurement results given by the manufacturer in the applicator certificate shows the measurement series of absolute dose using MCP-N thin layer detectors being in good accordance with the values of the applicator certificate. The dose values calculated with the source certificate can be confirmed with a maximum deviation of 6.5%. Further, it can be shown that compared to TLD-100, the use of MCP-N thermoluminescence detectors is an advantage, when calibrating with 6 MV photons. The phantom measuring procedure presented in this study provides a practice-oriented realization for quality control of ruthenium-106 ophthalmic applicators in clinical routine The phantom seems capable of performing periodic system tests, as well as controlling the introduction of new applicators delivered by the manufacturer.

A NEW TL-DOS NEUTRON DOSEMETER FOR MEASUREMENTS OF THE PERSONAL DOSE EQUIVALENT HP(10).

A new thermoluminescence albedo dosemeter with improved properties is developed as part of the TL-DOS project. The dosemeter measures the neutron and photon whole-body dose of radiation workers. The TL-DOS neutron dosemeter is presented and its results of well-known field measurements as well as field calibrations are shown. Its advantages, such as its potential to measure the high-linear energy transfer peaks, its improved detector sensitivity and long detector lifetime, are explained. The new dosemeter is compared to a thermoluminescence albedo dosemeter already used in routine dosimetry in Germany.

DETERMINATION OF THE PATIENTS' EFFECTIVE DOSES FOR MOST COMMON X-RAY EXAMINATIONS BY PHANTOM SIMULATION. / VYZNAChENNIa EFEKTYVNYKh DOZ PATsIIeNTIV PRY NAY̆BIL'Sh POShYRENYKh RENTGENOGRAFIChNYKh DOSLIDZhENNIaKh METODOM FANTOMNOGO MODELIuVANNIa.

OBJECTIVE: The objective of investigation is the determination of conversion factors from measured dosimetric values to equivalent organ / tissue doses by phantom modeling of the exposure conditions and assessment the effective doses of the «standard¼ patient for the most common types of radiographic examinations in Ukraine. MATERIALS AND METHODS: The simulation of patients' exposure for 7 most common types of radiographic exams and fluorography in Ukraine was carried out on a heterogeneous anthropomorphic phantom of a «standard¼ person. For phantom modeling two groups of X-ray units (modern digital and analogue units which have been in use for more than 15 years) were used. The measurements of entrance surface and absorbed doses in organs and tissues were per- formed using thermoluminescent dosimetry method. RESULTS: The conversional factors from the entrance surface doses (ESDs) to the equivalent doses for most radiosen- sitive organs / tissues of the «standard¼ patient were determined for the selected types of radiographic exams from the results of phantom simulations. The estimation of conversional factors from the ESDs to the effective doses was carried out in the working range of voltage values of two groups of X-ray units for the same radiographic examina- tions. A total of 116 phantom simulations were performed with 2-3 measurement repetitions for each irradiation model on each X-ray unit. CONCLUSIONS: The obtained values of conversion factors from ESD to the patients' effective doses for selected types of X-ray diagnostic exams can be used for assessing the effective doses of «standard¼ patients in the various X-ray rooms and for assessing the collective doses and radiation risks of the population of Ukraine due to the most com- mon radiographic examinations.

ANGULAR DEPENDENCE OF TRACK-ETCH DETECTOR HARZLAS TD-1.

Track-etched detectors are commonly used also for radiation monitoring onboard International Space Station. To be registered in track-etched detectors, the particle needs to meet several criteria-it must have linear energy transfer above the detection threshold and strike the detector's surface under an angle higher than the so-called critical angle. Linear energy transfer is then estimated from calibration curve from the etch rate ratio V that is calculated from parameters of individual tracks appearing on the detector's surface after chemical etching. It has been observed that V can depend on the incident angle and this dependence can vary for different detector materials, etching and evaluating conditions. To investigate angular dependence, detectors (Harzlas TD-1) were irradiated at HIMAC by several ions under angles from 0° to 90°. The correction accounting not only for critical angle but also for dependence of V on the incident angle is introduced and applied to spectra measured onboard International Space Station.

STUDY OF EFFECT OF CONSECUTIVE HEATING ON THERMOLUMINESCENCE GLOW CURVES OF MULTI-ELEMENT TL DOSEMETER IN HOT GAS-BASED READER SYSTEM.

The objective of this paper is to study the effect of consecutive heating of TL elements of a thermoluminescence dosemeter (TLD) card in hot N2 gas-based TLD badge reader. The effect is studied by theoretical simulations of clamped heating profiles of the discs and resulting TL glow curves. The simulated temperature profile accounts for heat transfer to disc from hot gas as well as radiative and convective heat exchanges between the disc and the surrounding. The glow curves are simulated using 10 component glow peak model for CaSO4:Dy using the simulated temperature profile. The shape of the simulated glow curves and trend in total TL signal of the three discs were observed to match closely with the experimental observations when elevated surrounding temperature was considered for simulation. It is concluded that the readout (heating) of adjacent TLD disc affects the surrounding temperature leading to the changes in temperature profile of the next disc.

Efficacy of the Monte Carlo method and dose reduction strategies in paediatric panoramic radiography.

Monte Carlo (MC) simulation is a simpler radiation dose assessment method than the conventional method, thermoluminescent dosimetry (TLD). MC simulation and TLD were compared as tools to evaluate the effective dose from paediatric panoramic radiography. Various exposure conditions and machine geometries were simulated using the MC method to investigate factors resulting in effective dose reduction. The effective dose of paediatric panoramic radiography was obtained using an MC simulation and its reliability was verified by a comparison with the value obtained using TLD. Next, 7 factors determining the effective dose in the MC simulation were input with 6 equally-spaced values, and a total of 36 simulations were performed to obtain effective dose values. The correlations between each dose-determining factor and the resulting effective dose were evaluated using linear regression analysis. The TLD-measured dose was 3.850 µSv, while the MC simulation yielded a dose of 3.474 µSv. Beam height was the factor that most strongly influenced the effective dose, while rotation angle and focus-to-patient distance were the least influential factors. MC simulation is comparable to TLD for obtaining effective dose values in paediatric panoramic radiography. Obtaining panoramic radiography with a short beam height can effectively reduce the dose in paediatric patients.

LOSS OF TLD SIGNAL DUE TO HIGH TEMPERATURE ENVIRONMENTAL CONDITIONS.

While it is known that temperatures above 100°C have an effect on the reported dose of a TLD, it is less widely known what the susceptibility is to temperatures below 100°C, temperatures humans could reasonably expect to be exposed to. With the expanding nuclear industry in climates with more extreme temperatures, (e.g. United Arab Emirates and Saudi Arabia) the effect on a TLD if left on a dashboard of a car need to be evaluated. This research experimentally determined the extent of this thermal susceptibility by testing a range of high temperatures, 40°C - 90°C. The experimental results found that there is a statistically significant reduction in TLD-100H (natLiF:Mg,Cu,P) light output for TLDs there were exposed to temperatures as low as 40°C for 8 hour durations and 50°C for 2 hour durations. There is statistical difference in TLD-100H light output for elevated temperature durations of 8 hours compared to 24 hours.

Response of TL and OSL passive personal dosimetry systems in poly-energetic and multi-directional photon radiation fields.

The aim of this paper is to examine the energy and angular responses of thermoluminescent dosimeters containing either MTS-N (LiF:Mg,Ti) or MCP-N (LiF:Mg,Cu,P) detector materials, and of the InLight optically stimulated luminescent dosimeters containing Al2O3:C detectors. Ten radiation qualities, with mean energies ranging from 24 keV to 1.25 MeV, and five angles of incidence, between 0° and 80°, were used for this purpose. The dosimeter response measure of quality were the IEC 62387 requirements. The experimental results show that the MTS-N-based and the InLight dosimeters performed in line with the standard's criteria. On the other hand, the MCP-N-based dosimeters exhibited a pronounced under-response around the energy of 120 keV, which resulted in deviations from the standard's conditions for both the energy and angular responses.