Age-dependent baseline variations in electron spin resonance signals of fingernails

Human nails have been studied for many years for potential use for dosimetry, based on the EPR signals induced by ionizing radiation, but a fully validated protocol to measure doses retrospectively has not yet been developed. The major problem is that the EPR spectrum of irradiated nails is complex and its radiation-induced signals (RIS) overlap with an endogenous signal called the background signal (BKS). RIS and BKS have similar spectral parameters. Therefore, detailed characterization of the BKS is required to develop a method for measuring the amount of RIS by removing the signal due to BKS from the total spectrum of irradiated nails. Effects of reducing and oxidizing treatments of fingernail samples on the BKS were studied. Numerical simulations of the observed BKSs were performed. Common features of the EPR spectra in fingernails are discussed. We also found that BKS can be generated in the fingernail clippings by oxidation in ambient air with dioxygen. Results support the hypothesis that BKS is an o-semiquinone radical anion. Comparison of the chemical and spectral properties of the BKS and with the RIS 5 (the stable signal suitable for dose assessment) suggests that both sets of radicals underlying these signals are o-semiquinone radicals. Given the common chemical properties of the BKS and RIS 5, it is unlikely that chemical treatment methods will provide a way to differentiate these two signals in irradiated nail spectra. Instead, other methods (i.e., dose-additive methods, population-derived BKS means) may be necessary to selectively estimate the content of BKS and RIS 5 in irradiated nail spectra.

There is an imperative need to develop methods that can rapidly and accurately determine individual exposure to radiation for screening (triage) populations and guiding medical treatment in an emergency response to a large-scale radiological/nuclear event. To this end, a number of methods that rely on dose-dependent chemical and/or physical alterations in biomaterials or biological responses are in various stages of development. One such method, ex vivo electron paramagnetic resonance (EPR) nail dosimetry using human nail clippings, is a physical biodosimetry technique that takes advantage of a stable radiation-induced signal (RIS) in the keratin matrix of fingernails and toenails. This dosimetry method has the advantages of ubiquitous availability of the dosimetric material, easy and non-invasive sampling, and the potential for immediate and rapid dose assessment. The major challenge for ex vivo EPR nail dosimetry is the overlap of mechanically induced signals and the RIS. The difficulties of analysing the mixed EPR spectra of a clipped irradiated nail were addressed in the work described here. The following key factors lead to successful spectral analysis and dose assessment in ex vivo EPR nail dosimetry: (1) obtaining a thorough understanding of the chemical nature, the decay behaviour, and the microwave power dependence of the EPR signals, as well as the influence of variation in temperature, humidity, water content, and O₂ level; (2) control of the variability among individual samples to achieve consistent shape and kinetics of the EPR spectra; (3) use of correlations between the multiple spectral components; and (4) use of optimised modelling and fitting of the EPR spectra to improve the accuracy and precision of the dose estimates derived from the nail spectra. In the work described here, two large clipped nail datasets were used to test the procedures and the spectral fitting model of the results obtained with it. A 15-donor nail set with 90 nail samples from 15 donors was used to validate the sample handling and spectral analysis methods that have been developed but without the interference of a native background signal. Good consistency has been obtained between the actual RIS and the estimated RIS computed from spectral analysis. In addition to the success in RIS estimation, a linear dose response has also been achieved for all individuals in this study, where the radiation dose ranges from 0 to 6 Gy. A second 16-donor nail set with 96 nail samples was used to test the spectral fitting model where the background signal was included during the fitting of the clipped nail spectra data. Although the dose response for the estimated and actual RIS calculated in both donor nail sets was similar, there was an increased variability in the RIS values that was likely due to the variability in the background signal between donors. Although the current methods of sample handling and spectral analysis show good potential for estimating the RIS in the EPR spectra of nail clippings, there is a remaining degree of variability in the RIS estimate that needs to be addressed; this should be achieved by identifying and accounting for demographic sources of variability in the background nail signal and the composition of the nail matrix.

Comparative study on the impact of storage conditions on ESR signals in fingernail dosimetry

While it is recognized that some medical workers could receive significantly higher radiation doses to their hands than the routinely monitored personal doses, accurate retrospective dosimetry of their hand exposure is still challenging. To solve this issue, a combination of electron spin resonance (ESR) measurement and fingernails is worth to be investigated. However, the application of fingernail ESR dosimetry requires establishing an effective protocol to eliminate the background signal (BKG) which changes due to mechanical stress and other unclear factors, so that the radiation doses would be precisely evaluated from the radiation-induced signals (RIS) only. Thus, the authors investigated possible applications of antioxidants to remove or reduce the BKG in fingernails. In the present study, the effectiveness of chemical treatment using the dithiothreitol (DTT) reducing reagent was examined in irradiated and unirradiated fingernails. Chemically and non-chemically treated fingernails were subsequently exposed to 20 Gy of 137Cs γ-rays and the time changes of the BKG and RIS were confirmed in two different storage conditions: vacuum chamber and freezer. The results show that the non-chemically treated fingernails displayed significant intra-individual variations in the peak-to-peak intensities of both BKG and RIS. RIS from chemically and non-chemically treated samples showed correlations after freezer storage; signals were more stable than the samples stored in the vacuum chamber. Moreover, while the BKG of non-chemically treated samples demonstrated higher levels than those chemically treated, the intra-individual variations were further reduced by the DTT treatment. Our results imply that the use of an antioxidant for hand washing of medical workers prior to starting their work could be effective in reducing the pre-existing free radicals in their fingernails. This also suggests a practical application of hand exposure monitoring using fingernails as a part of radiological emergency preparedness in occupations where radiation or radionuclides are used. Research for finding safer and easier-to-handle antioxidants is to be focused on in future studies.

Thermoluminescence and phototransferred thermoluminescence measurements of protective glass from smartphones are described. Samples of Gorilla Glass were examined from nine different manufacturers and 40 different phone models. Additionally, 12 glasses believed to be original equipment manufacturer replacements, as well as three glass samples from U.S. finishers, were also studied. Altogether, 99 different Gorilla Glass samples were examined. The radiation-induced thermoluminescence signal produced glow curve shapes specific to the Gorilla Glass generations and could be used to distinguish between them. A background thermoluminescence (and phototransferred thermoluminescence) signal was found in all unirradiated samples. Its intensity and shape were found to be dependent on the Gorilla Glass generation, phone manufacturer, and phone model. The background signal was demonstrated to be produced by ultraviolet light exposure; the shape of the background signal was able to be reproduced by the combined exposure to a broad-spectrum solar simulator and a 302 nm ultraviolet light source. The background signal intensity was found to vary with the location from which it was taken on the glass. It was also found to be dependent on the depth within the Gorilla Glass due to absorption of the ultraviolet light as it traversed the medium. Removal of the glasses’ surface layers was found to be an inadequate method for removing the background signal. In some samples, the background signal intensity was large enough to significantly contribute to the total thermoluminescence (and phototransferred thermoluminescence) signal; therefore, a matrix deconvolution method was introduced to separate the background signal and radiation-induced signal. This method was found to enable dose reconstruction using the radiation-induced signal alone.

IntroductionIndustrial and medical applications of ionizing radiation, as well as unstable political situation worldwide, which may result in military releases of radioactivity, increase a risk of uncontrolled exposures of people to ionizing radiation. Retrospective dosimetry allowing for fast triage of victims is crucial for rescue actions. Previous studies showed that smartphones’ screens are promising for dosimetry based on electron paramagnetic resonance (EPR). A variety of EPR line-shapes in different screens, regarding background signals (BG) and radiation-induced signals (RIS), various sensitivities to interfering factors like UV light and temperature, impose serious limitations on this method. This study focuses on classification of screen glasses, taking into account their elemental compositions, EPR properties (sensitivity to UV and temperature), in order to formulate practical recommendations for dosimetry.MethodsEPR spectra of 45 screens, unirradiated and irradiated with X-rays, were measured. Elemental composition of the glasses was determined using Energy Dispersive Spectroscopy. Effects of UV on samples’ EPR spectra were checked. Annealing at 200 °C enabled to evaluate effects of heating on BG and RIS. A self-written program based on c-means algorithm was used to find intercorrelations between elemental compositions and EPR features (types) of the glasses.Results and discussionOur spectra-differentiating algorithm resulted in identification of five types of glasses correlated with their elemental composition, sensitivity to X-rays, to UV and high temperature. Glasses labelled as type III and V were recommended for dosimetry due to their resistance to UV and undergoing temperature-caused bleaching of RIS without affecting their BG signals; a feature which enables reconstruction of the original BG from an irradiated sample – a key step in retrospective dosimetry. The introduced categorization of screen glasses, based on chosen features of their EPR spectra, is a simple and practical method for evaluation of their applicability in retrospective dosimetry following radiation accidents, e.g. for triage of exposed people.

Biodosimetry is crucial for assessing ionizing radiation exposure to guide medical responses. Electron spin resonance (ESR) spectroscopy using fingernails can be effectively used for both occupational and public dose assessments in radiological accidents because of their accessibility and ability to retain stable radiation-induced free radicals. However, despite two decades of research, challenges remain in achieving accurate fingernail dosimetry, mainly owing to the variation in ESR signals among individuals. The purpose of this study was to explore inter-individual differences in ESR signals in fingernails to improve the accuracy and reliability of extremity dosimetry. Fingernail samples were collected from 15 participants (age: 11-64 years), irradiated with X-rays (160 kV, 6.3 mA) at 0, 5, 10, and 20 Gy, and measured using ESR spectroscopy. The effects of individual factors, such as age, sex, health condition, and lifestyle, on radiation-induced ESR signals (RIS) were investigated. Younger participants exhibited stronger RIS intensities and a more linear dose-response relationship. The RIS intensity in female samples tended to be higher than that in male samples. Interestingly, the fingernals of middle-aged donors who regularly took vitamin supplements showed significantly higher ESR signal intensities than those of similar-age donors who did not take supplements. Notable reductions in RIS intensity during storage in a freezer were observed only in older donor samples irradiated at higher doses. These findings underscores the importance of considering age and other individual factors in the calibration for fingernail dosimetry.

Effect of spectrum processing procedure on the linearity of EPR dose reconstruction in tooth enamel

This study is about the accuracy of EPR dosimetry in bones based on deconvolution of the experimental spectra into the background (BG) and the radiation-induced signal (RIS) components. The model RIS's were represented by EPR spectra from irradiated enamel or bone powder; the model BG signals by EPR spectra of unirradiated bone samples or by simulated spectra. Samples of compact and trabecular bones were irradiated in the 30-270 Gy range and the intensities of their RIS's were calculated using various combinations of those benchmark spectra. The relationships between the dose and the RIS were linear (R2>0.995), with practically no difference between results obtained when using signals from irradiated enamel or bone as the model RIS. Use of different experimental spectra for the model BG resulted in variations in intercepts of the dose-RIS calibration lines, leading to systematic errors in reconstructed doses, in particular for high- BG samples of trabecular bone. These errors were reduced when simulated spectra instead of the experimental ones were used as the benchmark BG signal in the applied deconvolution procedures.

This study investigates the use of electron spin resonance (ESR) signals from human fingernails for retrospective dosimetry as part of radiation disaster response, focusing on the variabilities of individual responses to radiation. Samples of fingernails were collected from 7 adult donors (Asian type) and irradiated to 35 Gy and 70 Gy of gamma-rays from a Cs-137 source at a dose rate of 0.857 Gy/min. All irradiated fingernails were measured for 39 days with an X-band ESR spectrometer and stored in darkness inside the vacuum desiccator (30% humidity, 20°C) in between measurements at all times. All samples were harvested using one specific nail cutter and given no other special treatments. It was observed that the measured radiation-induced signals faded on about 10-12% after 1 day of exposure. Though the signal intensities showed a significant difference among the donors, stronger linearities in the dose responses were observed in the samples of younger donors. From the results obtained in this study, it is expected that fingernails would be a useful tool for retrospective dosimetry in case of an unexpected radiological accident or medical treatment error associated with exposure in therapeutic dose range, as far as the individual-based calibration curves were available. Further investigations will be made to clarify the reason for the different responses by using the fingernail samples taken from a greater number of donors of different ages and lifestyles.

The article describes effects of sample conditions during its irradiation and electron paramagnetic resonance (EPR) measurements on the background (BG) and dosimetric EPR signals in bone. Intensity of the BG signal increased up to two to three times after crushing of bone to sub-millimetre grains. Immersion of samples in water caused about 50 % drop in intensity of the BG component followed by its regrowth in 1-2 months. Irradiation of bone samples produced an axial dosimetric EPR signal (radiation-induced signal) attributed to hydroxyapatite component of bone. This signal was stable and was not affected by water. In samples irradiated in dry conditions, EPR signal similar to the native BG was also generated by radiation. In samples irradiated in wet conditions, this BG-like component was initially much smaller than in bone irradiated as dry, but increased in time, reaching similar levels as in dry-irradiated samples. It is concluded that accuracy of EPR dosimetry in bones can be improved, if calibration of the samples is done by their irradiations in wet conditions.

The results of the investigation of the effect of mobile phone radiation on the formation of electron paramagnetic resonance (EPR) spectra and electromagnetic noise on the example of measurements of dental enamel samples for the low dose range are presented. To this end, spectra of irradiated dental samples were obtained. The spectra of ten samples irradiated in nominal doses of 0, 100, 200, 300 and 500 mGy in pairs were registered at different times with and without a mobile phone. The mobile phone was located near the resonator of the EPR spectrometer. Specially software was used to extract the radiation-induced signal (RIS) from the full EPR spectrum and determine its intensity. As mentioned above to study the effect of the mobile phone signal on the EPR signal in this study, the radiation signal (RIS) (standard deviation (SD)) will be estimated by the background signal and the residual amount. These parameters were obtained for single measurements and, on average, for four repeated measurements.

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.

In this paper, we report results of radiation dose measurements in fingernails of a worker who sustained a radiation injury to his right thumb while using 130 kVp X-ray for nondestructive testing. Clinically estimated absorbed dose was about 20-25 Gy. Electron paramagnetic resonance (EPR) dose assessment was independently carried out by two laboratories, the Naval Dosimetry Center (NDC) and French Institut de Radioprotection et de Sûreté Nucléaire (IRSN). The laboratories used different equipments and protocols to estimate doses in the same fingernail samples. NDC used an X-band transportable EPR spectrometer, e-scan produced by Bruker BioSpin, and a universal dose calibration curve. In contrast, IRSN used a more sensitive Q-band stationary spectrometer (EMXplus) with a new approach for the dose assessment (dose saturation method), derived by additional dose irradiation to known doses. The protocol used by NDC is significantly faster than that used by IRSN, nondestructive, and could be done in field conditions, but it is probably less accurate and requires more sample for the measurements. The IRSN protocol, on the other hand, potentially is more accurate and requires very small amount of sample but requires more time and labor. In both EPR laboratories, the intense radiation-induced signal was measured in the accidentally irradiated fingernails and the resulting dose assessments were different. The dose on the fingernails from the right thumb was estimated as 14 ± 3 Gy at NDC and as 19 ± 6 Gy at IRSN. Both EPR dose assessments are given in terms of tissue kerma. This paper discusses the experience gained by using EPR for dose assessment in fingernails with a stationary spectrometer versus a portable one, the reasons for the observed discrepancies in dose, and potential advantages and disadvantages of each approach for EPR measurements in fingernails.

In this study, samples of smart phone touch screen glass sheets and tempered glass screen protectors were examined with respect to their potential application in the dosimetry of ionizing radiation. The glass samples were obtained from various phones with different types of glass. Electron paramagnetic resonance (EPR) spectra of the radiation-induced signals (RIS) are presented and their dose dependence within a dose range of 0–20 Gy. Despite the observed fading with time of the dosimetric components of the signal, the remaining RIS turned out to be strong enough for a reliable dosimetry even 18 month after irradiation. The study also shows that crushing of the glass sheets and water treatment of the samples have no effect on the background and dosimetric EPR signals.