Electron paramagnetic resonance dose measurements in teeth of tissue donors to the United States Transuranium and Uranium Registries

The United States Transuranium and Uranium Registries (USTUR) is a research program that studies actinide biokinetics in occupationally exposed individuals with known intakes of these elements. Electron paramagnetic resonance (EPR) in tooth enamel was applied to reconstruct external doses of nine USTUR registrants. Only in two cases there is a reasonable agreement between the EPR-measured dose and the worksite external dose record. For two registrants, high EPR doses can be explained by possible cancer radiotherapy. For the remaining five cases, EPR doses significantly exceed official occupational doses with no plausible explanation for the observed discrepancy. More EPR dose measurements need to be done to explain this anomaly.

RENEB Inter-Laboratory Comparison 2021: Inter-Assay Comparison of Eight Dosimetry Assays

Tools for radiation exposure reconstruction are required to support the medical management of radiation victims in radiological or nuclear incidents. Different biological and physical dosimetry assays can be used for various exposure scenarios to estimate the dose of ionizing radiation a person has absorbed. Regular validation of the techniques through inter-laboratory comparisons (ILC) is essential to guarantee high quality results. In the current RENEB inter-laboratory comparison, the performance quality of established cytogenetic assays [dicentric chromosome assay (DCA), cytokinesis-block micronucleus assay (CBMN), stable chromosomal translocation assay (FISH) and premature chromosome condensation assay (PCC)] was tested in comparison to molecular biological assays [gamma-H2AX foci (gH2AX), gene expression (GE)] and physical dosimetry-based assays [electron paramagnetic resonance (EPR), optically or thermally stimulated luminescence (LUM)]. Three blinded coded samples (e.g., blood, enamel or mobiles) were exposed to 0, 1.2 or 3.5 Gy X-ray reference doses (240 kVp, 1 Gy/min). These doses roughly correspond to clinically relevant groups of unexposed to low exposed (0-1 Gy), moderately exposed (1-2 Gy, no severe acute health effects expected) and highly exposed individuals (>2 Gy, requiring early intensive medical care). In the frame of the current RENEB inter-laboratory comparison, samples were sent to 86 specialized teams in 46 organizations from 27 nations for dose estimation and identification of three clinically relevant groups. The time for sending early crude reports and more precise reports was documented for each laboratory and assay where possible. The quality of dose estimates was analyzed with three different levels of granularity, 1. by calculating the frequency of correctly reported clinically relevant dose categories, 2. by determining the number of dose estimates within the uncertainty intervals recommended for triage dosimetry (±0.5 Gy or ±1.0 Gy for doses <2.5 Gy or >2.5 Gy), and 3. by calculating the absolute difference (AD) of estimated doses relative to the reference doses. In total, 554 dose estimates were submitted within the 6-week period given before the exercise was closed. For samples processed with the highest priority, earliest dose estimates/categories were reported within 5-10 h of receipt for GE, gH2AX, LUM, EPR, 2-3 days for DCA, CBMN and within 6-7 days for the FISH assay. For the unirradiated control sample, the categorization in the correct clinically relevant group (0-1 Gy) as well as the allocation to the triage uncertainty interval was, with the exception of a few outliers, successfully performed for all assays. For the 3.5 Gy sample the percentage of correct classifications to the clinically relevant group (≥2 Gy) was between 89-100% for all assays, with the exception of gH2AX. For the 1.2 Gy sample, an exact allocation to the clinically relevant group was more difficult and 0-50% or 0-48% of the estimates were wrongly classified into the lowest or highest dose categories, respectively. For the irradiated samples, the correct allocation to the triage uncertainty intervals varied considerably between assays for the 1.2 Gy (29-76%) and 3.5 Gy (17-100%) samples. While a systematic shift towards higher doses was observed for the cytogenetic-based assays, extreme outliers exceeding the reference doses 2-6 fold were observed for EPR, FISH and GE assays. These outliers were related to a particular material examined (tooth enamel for EPR assay, reported as kerma in enamel, but when converted into the proper quantity, i.e. to kerma in air, expected dose estimates could be recalculated in most cases), the level of experience of the teams (FISH) and methodological uncertainties (GE). This was the first RENEB ILC where everything, from blood sampling to irradiation and shipment of the samples, was organized and realized at the same institution, for several biological and physical retrospective dosimetry assays. Almost all assays appeared comparably applicable for the identification of unexposed and highly exposed individuals and the allocation of medical relevant groups, with the latter requiring medical support for the acute radiation scenario simulated in this exercise. However, extreme outliers or a systematic shift of dose estimates have been observed for some assays. Possible reasons will be discussed in the assay specific papers of this special issue. In summary, this ILC clearly demonstrates the need to conduct regular exercises to identify research needs, but also to identify technical problems and to optimize the design of future ILCs.

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.

Retrospective Assessment of Exposures to Ionising Radiation: Abstract

Basic dose quantities used in dose reconstruction are defined. The following dose reconstruction methods based on measurements performed for individual persons are reviewed: electron paramagnetic resonance (EPR) measurements with tooth enamel, analyses of dicentric chromosomes and chromosome translocations, counting of micronuclei in lymphocytes, somatic-mutation assays, and measurements of radionuclide activities in the human body. Methods based on measurements in environmental media include luminescence methods applied to minerals to determine absorbed doses in ceramics such as bricks or porcelain, accelerator mass spectrometry (AMS) to determine small quantities of man-made long-lived radionuclides, methods based on existing measurements of absorbed dose rates in air, and modelling based on radionuclide activities in the environment. The application of different methods of dose reconstruction to the same individuals is reviewed for the atomic-bomb survivors of Hiroshima and Nagasaki (dosimetry system DS86, EPR with teeth, chromosomal aberrations in lymphocytes, and somatic-mutation assays) and the workers of the Mayak Production Association (occupational film badge dosimetry, EPR with teeth, and fluorescence in situ hybridisation (FISH) with lymphocytes). Examples of reconstruction of absorbed doses in environmental media are Hiroshima and Nagaski (luminescence measurements, AMS and the DS86 system), the Nevada test site (measurements of 137Cs activity in the soil, thermoluminescence of bricks and gamma dose rate in air), and settlements contaminated by the Chernobyl accident (luminescence methods and modelling based on measured 137Cs activity in the ground). The report concludes with an overview the conditions under which the various methods of the dose reconstruction are best applied.

State of the art in nail dosimetry: free radicals identification and reaction mechanisms

Until very recently, analysis of bone biopsies by means of the method of electron paramagnetic resonance (EPR) collected after surgery or amputation has been considered as the sole reliable method for radiation dose assessment in hands and feet. EPR measurements in finger- and toenail have been considered for accident dosimetry for a long time. Human nails are very attractive biophysical materials because they are easy to collect and pertinent to whole body irradiation. Information on the existence of a radiation-induced signal in human nails has been reported almost 25 years ago. However, no practical application of EPR dosimetry on nails is known to date because, from an EPR perspective, nails represent a very complex material. In addition to the radiation-induced signal (RIS), parasitic and intense signals are induced by the mechanical stress caused when collecting nail samples (mechanically induced signals-MIS). Moreover, it has been demonstrated that the RIS stability is strongly influenced not only by temperature but also by humidity. Most studies of human nails were carried out using conventional X-band microwave band (9 GHz). Higher frequency Q-band (37 GHz) provides higher spectral resolution which allows obtaining more detailed information on the nature of different radicals in human nails. Here, we present for the first time a complete description of the different EPR signals identified in nails including parasitic, intrinsic and RIS. EPR in both X- and Q-bands was used. Four different MIS signals and five different signals specific to irradiation with ionizing radiation have been identified. The most important outcome of this work is the identification of a stable RIS component. In contrast with other identified (unstable) RIS components, this component is thermally and time stable and not affected by the physical contact of fingernails with water. A detailed description of this signal is provided here. The discovery of stable radiation-induced radical(s) associated with the RIS component mentioned opens a way for broad application of EPR dosimetry in human nails. Consequently, several recent dosimetry assessments of real accident cases have been performed based on the described measurements and analyses of this component.

Intercomparison exercise within a distributed-dosimetry network

The results of an intercomparison exercise within the US Navy dosimetric network (USN-DN) are presented and discussed. The USN-DN uses a commercially available LiF:Mg,Cu,P thermoluminescent dosemeter (TLD) model Harshaw 8840/8841 and TLD reader model Harshaw 8800 manufactured by Thermo Fisher Scientific. The USN-DN consists of a single calibration facility and 16 satellite dosimetry reading facilities throughout the world with ∼ 40 model 8800 TLD readers and in excess of 350 000 TLD cards in circulation. The Naval Dosimetry Center (NDC) is the primary calibration site responsible for the distribution and calibration of all TLD cards and their associated holders. In turn, each satellite facility is assigned a subpopulation of cards, which are utilised for servicing their local customers. Consistency of the NDC calibration of 150 dosemeters (calibrated at NDC) and 27 locally calibrated remote readers was evaluated in the framework of this intercomparison. Accuracy of TLDs' calibration, performed at the NDC, was found to be <3 % throughout the entire network. Accuracy of the readers' calibration, performed with the NDC issued calibration dosemeters at remote sites, was found to be better than 4 % for most readers. The worst performance was found for reader Channel 3, which is calibrated using the thinnest chip of the Harshaw 8840/8841 dosemeter. The loss of sensitivity of this chip may be caused by time-temperature profile that has been designed for all four chips without consideration of chip thickness.

The applicability of the PTTL dose re-analysis method to the Harshaw LiF:Mg,Cu,P material

The phototransferred thermoluminescence (PTTL) technique is applied to the Harshaw LiF:Mg,Cu,P material. It is demonstrated that using 254-nm UV light, dose levels as low as 0.2 mGy can be re-estimated. The PTTL efficiency was found to be ∼ 6 % in the dose range of 0.2 mGy-1 Gy, and it appears to be dose-independent. This implies that a simple calibration factor could be applied to the PTTL data for the re-estimation of dose levels. It was demonstrated that with a proper choice of the TL readout parameters, and the UV-light irradiation conditions, dose levels that are relevant to personal or environmental dosimetry can be re-estimated.

Uncertainties associated with the use of optically stimulated luminescence in personal dosimetry

This study investigates several sources of uncertainty associated with the application of optically stimulated luminescence (OSL) to personal dosimetry. A commercial OSL system based on Al(2)O(3):C was used for this study. First, it is demonstrated that the concept of repeated evaluation (readout) of the same dosemeter, often referred to as 're-analysis', can introduce uncertainty in the re-estimated dose. This uncertainty is associated with the fact that the re-analysis process depletes some of the populated traps, resulting in a continuous decrease of the OSL signal with each repeated reading. Furthermore, the rate of depletion may be dose-dependent. Second, it is shown that the previously reported light-induced fading in this system is the result of light leaks through miniature openings in the dosemeter badge.

Overview of physical and biophysical techniques for accident dosimetry

From feedback experience from recent radiation accident cases, in addition to biological dosimetry and physical dosimetry based on Monte Carlo calculations or experimental means, there is a need for complementary methods of dosimetry for radiation accident. Electron paramagnetic resonance (EPR) spectrometry on bones or teeth is considered as efficient but is limited by the invasive character of the sampling. Since 2005, Institute for Radiological Protection and Nuclear Safety (IRSN) develops some new approaches and methodologies based on the EPR and luminescence techniques. This article presents the overview of the different studies currently in progress in IRSN.

Electron paramagnetic resonance in human fingernails: the sponge model implication

The most significant problem of electron paramagnetic resonance (EPR) fingernail dosimetry is the presence of two signals of non-radiation origin that overlap the radiation-induced signal (RIS), making it almost impossible to perform dose measurements below 5 Gy. Historically, these two non-radiation components were named mechanically induced signal (MIS) and background signal (BKS). In order to investigate them in detail, three different methods of MIS and BKS mutual isolation have been developed and implemented. After applying these methods, it is shown here that fingernail tissue, after cut, can be modeled as a deformed sponge, where the MIS and BKS are associated with the stress from elastic and plastic deformations, respectively. A sponge has a unique mechanism of mechanical stress absorption, which is necessary for fingernails in order to perform its everyday function of protecting the fingertips from hits and trauma. Like a sponge, fingernails are also known to be an effective water absorber. When a sponge is saturated with water, it tends to restore to its original shape, and when it loses water, it becomes deformed again. The same happens to fingernail tissue. It is proposed that the MIS and BKS signals of mechanical origin be named MIS1 and MIS2 for MISs 1 and 2, respectively. Our suggested interpretation of the mechanical deformation in fingernails gives also a way to distinguish between the MIS and RIS. The results obtained show that the MIS in irradiated fingernails can be almost completely eliminated without a significant change to the RIS by soaking the sample for 10 min in water. The proposed method to measure porosity (the fraction of void space in spongy material) of the fingernails gave values of 0.46-0.48 for three of the studied samples. Existing results of fingernail dosimetry have been obtained on mechanically stressed samples and are not related to the "real" in vivo dosimetric properties of fingernails. A preliminary study of these properties of pre-soaked (unstressed) fingernails has demonstrated their significant difference from fingernails stressed by cut. They show a higher stability signal, a less intensive non-radiation component, and a nonlinear dose dependence. The findings in this study set the stage for understanding fingernail EPR dosimetry and doing in vivo measurements in the future.

Long-term fade study of the DT-702 LiF: Mg,Cu,P TLD

LiF thermoluminescent dosemeters (TLDs) are used by the US Navy to record radiation exposure of personnel. The Model DT-648 LiF:Mg,Ti TLD has been replaced by a new Model DT-702 LiF:Mg,Cu,P TLD. The DT-648 was used for many years and has undergone extensive testing to identify its pre- and post-irradiation fade operating characteristics. Studies have shown that the addition of copper increases the thermoluminesence sensitivity of the TLD for improved low-level radiation monitoring. This study evaluates various fading characteristics of the new copper-doped dosemeter using current equipment for processing of TLDs and calibrating to a National Institute of Standards and Technology standard source. The 57-week study took place at the Naval Dosimetry Center, Bethesda, MD, USA. TLDs were stored for various lengths of time before and after being exposed to a National Institute of Standards and Technology calibrated radiation sources. TLDs were then processed using current US Navy instructions and the resulting dose compared with the calibrated exposure. Both loss of signal and loss of sensitivity were evaluated. The results of this study have shown that the DT-702 TLD has no statistically significant change in sensitivity or change in signal with up to 57 weeks of pre- or post-irradiation time. The results of this study will increase the accuracy of exposure record keeping for the Navy and will allow longer issue periods. This will increase flexibility with international and domestic shipping procedures, as well as reduce workload requirements for dosimetry processing.

Q-band EPR biodosimetry in tooth enamel microsamples: feasibility test and comparison with x-band

A comparative study of electron paramagnetic resonance dosimetry in Q- and X-bands has shown that Q-band is able to provide accurate measurements of radiation doses even below 0.5 Gy with tooth enamel samples as small as 2 mg. The optimal amount of tooth enamel for dose measurements in Q-band was found to be 4 mg. This is less than 1% of the total amount of tooth enamel in one molar tooth. Such a small amount of tooth enamel can be harmlessly obtained in an emergency requiring after-the-fact radiation dose measurement. The other important advantage of Q-band is full resolution of the radiation-induced EPR signal from the native, background signal. This separation makes dose response measurements much easier in comparison to conventional X-band measurements in which these overlapping signals necessitate special methods for doses below 0.5 Gy. The main disadvantages of Q-band measurements are a higher level of noise and lower spectral reproducibility than in X-band. The effect of these negative factors on the precision of dose measurements in Q-band could probably be reduced by improvement of sample fixation in the resonance cavity and better optimization of signal filtration to reduce high-frequency noise.

Protocol for emergency EPR dosimetry in fingernails

There is an increased need for after-the-fact dosimetry because of the high risk of radiation exposures due to terrorism or accidents. In case of such an event, a method is needed to make measurements of dose in a large number of individuals rapidly and with sufficient accuracy to facilitate effective medical triage. Dosimetry based on EPR measurements of fingernails potentially could be an effective tool for this purpose. This paper presents the first operational protocols for EPR fingernail dosimetry, including guidelines for collection and storage of samples, parameters for EPR measurements, and the method of dose assessment. In a blinded test of this protocol application was carried out on nails freshly sampled and irradiated to 4 and 20 Gy; this protocol gave dose estimates with an error of less than 30%.

EPR dosimetry in chemically treated fingernails

By using EPR measurements of radiation-induced radicals it is possible to utilize human fingernails to estimate radiation dose after-the-fact. One of the potentially limiting factors in this approach is the presence of artifacts due to mechanically induced EPR signals (MIS) caused by mechanical stress during the collection and preparation of the samples and the so-called background (non-radiation) signal (BKS). The MIS and BKS have spectral parameters (shape, g-factor and linewidth) that overlap with the radiation-induced signal (RIS) and therefore, if not taken into account properly, could result in a considerable overestimation of the dose. We have investigated the use of different treatments of fingernails with chemical reagents to reduce the MIS and BKS. The most promising chemical treatment (20 min with 0.1 M dithiothreitol aqueous solution) reduced the contribution of MIS and BKS to the total intensity of EPR signal of irradiated fingernails by a factor of 10. This makes it potentially feasible to measure doses as low as 1 Gy almost immediately after irradiation. However, the chemical treatment reduces the intensity of the RIS and modifies dose dependence. This can be compensated by use of an appropriate calibration curve for assessment of dose. On the basis of obtained results it appears feasible to develop a field-deployable protocol that could use EPR measurements of samples of fingernails to assist in the triage of individuals with potential exposure to clinically significant doses of radiation.

Comparison of EPR occupational lifetime external dose assessments for Mayak nuclear workers and film badge dose data

The Mayak worker cohort is one of the major sources of information on health risks due to protracted exposures to plutonium and external ionizing radiation. Electron paramagnetic resonance (EPR) measurements in tooth enamel in combination with personal dose monitoring can help to improve external dose assessment for this cohort. Here, the occupational lifetime external exposure was evaluated individually for 44 nuclear workers of three plants of the Mayak Production Association by EPR measurements of absorbed doses in collected tooth enamel samples. Analysis included consideration of individual background doses in enamel and dose conversion coefficients specific for photon spectra at selected work areas. As a control, background doses were assessed for various age groups by EPR measurements on teeth from non-occupationally exposed Ozyorsk residents. Differences in occupational lifetime doses estimated from the film badges and from enamel for the Mayak workers were found to depend on the type of film badge and the selected plant. For those who worked at the radiochemical processing plant and who were monitored with IFK film badges, the dose was on average 570 mGy larger than estimated from the EPR measurements. However, the average difference was found to be only -4 and 6 mGy for those who were monitored with IFKU film badges and worked at the reactor and the isotope production plant respectively. The discrepancies observed in the dose estimates are attributed to a bias in film badge evaluation.

Optimization of reading conditions for flat panel displays

Task Group 18 (TG 18) of the American Association of Physicists in Medicine has developed guidelines for Assessment of Display Performance for Medical Imaging Systems. In this document, a method for determination of the maximum room lighting for displays is suggested. It is based on luminance measurements of a black target displayed on each display device at different room illuminance levels. Linear extrapolation of the above luminance measurements vs. room illuminance allows one to determine diffuse and specular reflection coefficients. TG 18 guidelines have established recommended maximum room lighting. It is based on the characterization of the display by its minimum and maximum luminance and the description of room by diffuse and specular coefficients. We carried out these luminance measurements for three selected displays to determine their optimum viewing conditions: one cathode ray tube and two flat panels. We found some problems with the application of the TG 18 guidelines to optimize viewing conditions for IBM T221 flat panels. Introduction of the requirement for minimum room illuminance allows a more accurate determination of the optimal viewing conditions (maximum and minimum room illuminance) for IBM flat panels. It also addresses the possible loss of contrast in medical images on flat panel displays because of the effect of nonlinearity in the dependence of luminance on room illuminance at low room lighting.

The Third International Intercomparison on EPR Tooth Dosimetry: part 2, final analysis

The objective of the Third International Intercomparison on EPR Tooth Dosimetry was to evaluate laboratories performing tooth enamel dosimetry <300 mGy. Final analysis of results included a correlation analysis between features of laboratory dose reconstruction protocols and dosimetry performance. Applicability of electron paramagnetic resonance (EPR) tooth dosimetry at low dose was shown at two applied dose levels of 79 and 176 mGy. Most (9 of 12) laboratories reported the dose to be within 50 mGy of the delivered dose of 79 mGy, and 10 of 12 laboratories reported the dose to be within 100 mGy of the delivered dose of 176 mGy. At the high-dose tested (704 mGy) agreement within 25% of the delivered dose was found in 10 laboratories. Features of EPR dose reconstruction protocols that affect dosimetry performance were found to be magnetic field modulation amplitude in EPR spectrum recording, EPR signal model in spectrum deconvolution and duration of latency period for tooth enamel samples after preparation.

The 3rd international intercomparison on EPR tooth dosimetry: Part 1, general analysis

The objective of the 3rd International Intercomparison on Electron Paramagnetic Resonance (EPR) Tooth Dosimetry was the evaluation of laboratories performing tooth enamel dosimetry below 300 mGy. Participants had to reconstruct the absorbed dose in tooth enamel from 11 molars, which were cut into two halves. One half of each tooth was irradiated in a 60Co beam to doses in the ranges of 30-100 mGy (5 samples), 100-300 mGy (5 samples), and 300-900 mGy (1 sample). Fourteen international laboratories participated in this intercomparison programme. A first analysis of the results and an overview of the essential features of methods applied in different laboratories are presented. The relative standard deviation of results of all methods was better than 27% for applied doses in the range of 79-704 mGy. In the analysis of the unirradiated tooth halves 8% of the samples were identified as outliers with additional absorbed dose above background dose.

Comparison of three methods of numerical procedures for ESR dosimetry of human tooth enamel

Three numerical methods were employed to examine how gamma ray doses ranging from 100 mGy to 1Gy could be reconstructed using five human molar teeth. For samples above 28 0mGy, the obtained doses are consistent with each other within the errors but slightly larger than actually given doses. Background doses range from 20 to 170 mGy depending on the methods and samples. Further precise studies would be needed to characterize each method, but it would be recommended to apply several methods to check the reliability of the obtained doses.

Effect of room illuminance on monitor black level luminance and monitor calibration

In this article we demonstrate the effect of room illuminance and surrounding monitor black level luminance on image quality for soft copy interpretation. Luminance values of a 10% central target and image quality evaluations and observer performance using a contrast-detail mammography (CDMAM) phantom demonstrate these effects. Our results indicate that high room illuminance has a more damaging effect on image quality when the surrounding monitor luminance is 0% to 5% of the maximum monitor luminance. The effect of room illuminance is less obvious when the surrounding monitor luminance is 20% of the maximum.

Comparison of sample preparation and signal evaluation methods for EPR analysis of tooth enamel

In dose reconstruction by EPR dosimetry with teeth various methods are applied to prepare tooth enamel samples and to evaluate the dosimetric signal. A comparison of seven frequently used methods in EPR dosimetry with tooth enamel was performed. The participating Institutes have applied their own procedure to prepare tooth enamel samples and to evaluate the dosimetric signal. The precision of the EPR measurement and the dependence of the estimated dosimetric signal with irradiation up to 1000 mGy were compared. The obtained results are consistent among the different methods. The reproducibility of the dosimetric signal and its estimated relation with the absorbed dose was found to be very close for the applied methods with one possible exception.