Electron paramagnetic resonance radiation dose assessment in fingernails of the victim exposed to high dose as result of an accident.

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.

EPR dosimetry intercomparison using smart phone touch screen glass.

This paper presents the results of an interlaboratory comparison of retrospective dosimetry using the electron paramagnetic resonance method. The test material used in this exercise was glass coming from the touch screens of smart phones that might be used as fortuitous dosimeters in a large-scale radiological incident. There were 13 participants to whom samples were dispatched, and 11 laboratories reported results. The participants received five calibration samples (0, 0.8, 2, 4, and 10 Gy) and four blindly irradiated samples (0, 0.9, 1.3, and 3.3 Gy). Participants were divided into two groups: for group A (formed by three participants), samples came from a homogeneous batch of glass and were stored in similar setting; for group B (formed by eight participants), samples came from different smart phones and stored in different settings of light and temperature. The calibration curves determined by the participants of group A had a small error and a critical level in the 0.37-0.40-Gy dose range, whereas the curves determined by the participants of group B were more scattered and led to a critical level in the 1.3-3.2-Gy dose range for six participants out of eight. Group A were able to assess the dose within 20 % for the lowest doses (<1.5 Gy) and within 5 % for the highest doses. For group B, only the highest blind dose could be evaluated in a reliable way because of the high critical values involved. The results from group A are encouraging, whereas the results from group B suggest that the influence of environmental conditions and the intervariability of samples coming from different smart phones need to be further investigated. An alongside conclusion is that the protocol was easily transferred to participants making a network of laboratories in case of a mass casualty event potentially feasible.

Electron paramagnetic resonance in irradiated fingernails: variability of dose dependence and possibilities of initial dose assessment.

The results of electron paramagnetic resonance (EPR) measurements in irradiated fingernails are presented. In total, 83 samples of different fingernails were studied. Five different groups of samples were selected based on the collection time of fingernail samples, their level of mechanical stress, and the number and size of clippings: (1) recently (<24 h) cut, irradiated and measured with EPR without any treatment of samples, and with rigorous control of size and number of clippings (stressed-fresh, controlled); (2) recently (<24 h) cut, irradiated and measured with EPR after application of a special treatment (10 min of water soaking, 5 min of drying time) to reduce the mechanical stress caused by cutting the samples, and with rigorous control of size and number of clippings (unstressed-fresh, controlled); (3) previously (>24 h) cut, stored at room temperature, additionally cut into small pieces immediately prior to study, irradiated and measured with EPR without any treatment of samples, and with rigorous control of size and number of clippings (stressed-old, controlled); (4) previously (>24 h) cut, stored at room temperature, additionally cut into small pieces immediately prior to the study, irradiated and measured with EPR after application of a special treatment to reduce mechanical stress caused by cut, and with rigorous control of size and number of clippings (unstressed-old, controlled); and (5) recently (<24 h) cut, irradiated and measured with EPR after application of a special treatment to reduce the mechanical stress caused by cut, and without rigorous control of size and number of clippings (unstressed-fresh, uncontrolled). Except for the fifth selected group, variability of the dose dependence inside all groups was found to be not statistically significant, although the variability among the different groups was significant. Comparison of the mean dose dependences obtained for each group allowed selection of key factors responsible for radiation sensitivity (dose response per unit of mass and dose) and the shape of dose dependence in fingernails. The major factor responsible for radiation sensitivity of fingernails was identified as their water content, which can affect radiation sensitivity up to 35%. The major factor responsible for the shape of the radiation sensitivity was identified as the mechanical stress. At a significant level of mechanical stress, the shape of the dose dependence is linear in the studied dose range (<20 Gy), and in lesser-stressed samples it is of an exponential growth including saturation, which depends on the degree of mechanical stress. In view of the findings, recommendations are discussed and presented for the appropriate protocol for EPR dose measurements in fingernails.

CONCEPTS OF OPERATIONS FOR A US DOSIMETRY AND BIODOSIMETRY NETWORK.

The USA must be prepared to provide a prompt, coordinated and integrated response for radiation dose and injury assessment for suspected radiation exposure, whether it involves isolated cases or mass casualties. Dose estimation for radiation accidents typically necessitates a multiple parameter diagnostics approach that includes clinical, biological and physical dosimetry to provide an early-phase radiation dose. A US Individual Dosimetry and Biodosimetry Network (US-IDBN) will increase surge capacity for civilian and military populations in a large-scale incident. The network's goal is to leverage available resources and provide an integrated biodosimetry capability, using multiple parameter diagnostics. Initial operations will be to expand an existing functional integration of two cytogenetic biodosimetry laboratories by developing Standard Operating Procedures, cross-training laboratorians, developing common calibration curves, supporting inter-comparison exercises and obtaining certification to process clinical samples. Integration with certified commercial laboratories will increase surge capacity to meet the needs of a mass-casualty incident.

Acceptance Testing of Thermoluminescent Dosimeter Holders.

The U.S. Navy uses the Harshaw 8840/8841 dosimetric (DT-702/PD) system, which employs LiF:Mg,Cu,P thermoluminescent dosimeters (TLDs), developed and produced by Thermo Fisher Scientific (TFS). The dosimeter consists of four LiF:Mg,Cu,P elements, mounted in Teflon® on an aluminum card and placed in a plastic holder. The holder contains a unique filter for each chip made of copper, acrylonitrile butadiene styrene (ABS), Mylar®, and tin. For accredited dosimetry labs, the ISO/IEC 17025:2005(E) requires an acceptance procedure for all new equipment. The Naval Dosimetry Center (NDC) has developed and tested a new non-destructive procedure, which enables the verification and the evaluation of embedded filters in the holders. Testing is based on attenuation measurements of low-energy radiation transmitted through each filter in a representative sample group of holders to verify that the correct filter type and thickness are present. The measured response ratios are then compared with the expected response ratios. In addition, each element's measured response is compared to the mean response of the group. The test was designed and tested to identify significant nonconformities, such as missing copper or tin filters, double copper or double tin filters, or other nonconformities that may impact TLD response ratios. During the implementation of the developed procedure, testing revealed a holder with a double copper filter. To complete the evaluation, the impact of the nonconformities on proficiency testing was examined. The evaluation revealed failures in proficiency testing categories III and IV when these dosimeters were irradiated to high-energy betas.

Toward high sensitivity ESR dosimetry of mammal teeth: the effect of chemical treatment.

Investigations were conducted into chemical treatments suitable for concentrating enamel from cow teeth. Cow teeth could be used as alternative to human teeth for retrospective dosimetry when human teeth are not available. It is essential to remove dentin from tooth enamel for low dose radiation dosimetry in order to avoid interference to the ESR signal from organic radicals. Increasing the period of chemical treatment with KOH and NaOH reduced the signal intensity of the organic radicals. The sensitivity of the dosimetric signal from inorganic radicals increased slightly with length of treatment with NaOH, which is consistent with removal of dentin, and rose to a maximum of 20% after 5 h with KOH (40 degrees C).

90Sr concentration in cow teeth from South Ural region, Russia, using Monte Carlo simulation.

The Imaging Plate (IP) technique which uses the Monte Carlo code, MCNP, to convert IP response to 90Sr concentration with varied thickness of the standard source has been proposed in this study. In order to verify the validity of simulation calculation in the proposed method, the radial distribution of IP signal has been compared between calculation and experiment. The result is, they are in good agreement. The proposed method has been applied to a cow tooth from the territory contaminated by radioactivity after the accident in the Mayak facility in the South Ural, Russia. Two samples have been prepared from the tooth, i.e., a thin sample of 1.2+/-0.2 mm in thickness and a thick sample which is a half of the tooth. The IP response has been evaluated for the thick sample using experimentally made standard sources, and multiplied by a modification factor to decide that for the thin sample. The modification factor has been determined with MCNP to be 0.83+/-0.08 for a thickness of 1.2+/-0.2 mm. Using these values, 90Sr concentration has been estimated to be 0.11 Bq/g for the thin sample and 0.12 Bq/g for the thick sample, hence they are in good agreement.

Kevlar® as a Potential Accident Radiation Dosimeter for First Responders, Law Enforcement and Military Personnel.

Today the armed forces and law enforcement personnel wear body armor, helmets, and flak jackets composed substantially of Kevlar® fiber to prevent bodily injury or death resulting from physical, ballistic, stab, and slash attacks. Therefore, there is a high probability that during a radiation accident or its aftermath, the Kevlar®-composed body armor will be irradiated. Preliminary study with samples of Kevlar® foundation fabric obtained from body armor used by the U.S. Marine Corps has shown that all samples evaluated demonstrated an EPR signal, and this signal increased with radiation dose. Based on these results, the authors predict that, with individual calibration, exposure at dose above 1 Gy can be reliably detected in Kevlar® samples obtained from body armor. As a result of these measurements, a post-event reconstruction of exposure dose can be obtained by taking various samples throughout the armor body and helmet worn by the same irradiated individual. The doses can be used to create a whole-body dose map that would be of vital importance in a case of a partial body or heterogeneous exposure.

Effect of short-term sensitivity loss in LiF:Mg,Cu,P thermoluminescent dosemeter and its implications on personnel dosimetry operations.

A short-term sensitivity loss in LiF:Mg,Cu,P thermoluminescent dosemeters (TLDs) was observed and is described. Its observation occurred during a pre-irradiation anneal with a slightly elevated maximum temperature (5-15°C), which causes notable under-response (5-10 %) of the subsequent read at the recommended time-temperature profile (TTP), which has a peak temperature of 260°C. A subsequent irradiation and reading using the recommended TTP showed partial or complete recovery of the TLD's sensitivity. To the best of our knowledge, there were no publications on possible implications of a one-time 5-15°C overheat of LiF:Mg,Cu,P TLDs during anneal. This is not unusual when several readers with some variations in their heating cycles are used to calibrate and process the same population of dosemeters. A special test to identify if a small uncontrolled overheating of a dosemeter element has occurred was developed and tested. Two practical implications of the effect of a short-term sensitivity loss in LiF:Mg,Cu,P, e.g. inconsistency in results of metrological traceability verification and reporting of false neutron doses, are described in detail. Simple indicators of a small uncontrolled overheating are provided.

Comparison of Continuous Wave and Rapid Scan X-band Electron Paramagnetic Resonance of Irradiated Clipped Fingernails.

X-band rapid scan electron paramagnetic resonance (EPR) measures the free radicals in irradiated clipped fingernails with higher signal-to-noise (S/N) and lower standard deviation of the signal amplitude for replicate measurements than does conventional continuous wave (CW) EPR in the same measurement time. For a clipped fingernail sample irradiated to 10 Gy and data acquisition time of 30 s with B1 = 8.5 µT, the S/N for rapid scan is >2000 for the absorption spectrum and 1200 for the corresponding first derivative. The standard deviation for replicate measurements of signal amplitude is ~1%. For CW spectra, the S/N depends on the modulation amplitude. The CW signal has a first derivative peak-to-peak linewidth of 0.95 mT. For 30 s of CW acquisition time, the S/N was 30 for a conservative modulation amplitude of 0.2 mT and B1 of 2.3 µT or 90 for a modulation amplitude of 0.4 mT and B1 of 3.2 µT, which resulted in standard deviations of replicate measurements of 5% or 2%, respectively.

U.S. Department of Defense Multiple-Parameter Biodosimetry Network.

The U.S. Department of Defense (USDOD) service members are at risk of exposure to ionizing radiation due to radiation accidents, terrorist attacks and national defense activities. The use of biodosimetry is a standard of care for the triage and treatment of radiation injuries. Resources and procedures need to be established to implement a multiple-parameter biodosimetry system coupled with expert medial guidance to provide an integrated radiation diagnostic system to meet USDOD requirements. Current USDOD biodosimetry capabilities were identified and recommendations to fill the identified gaps are provided. A USDOD Multi-parametric Biodosimetry Network, based on the expertise that resides at the Armed Forces Radiobiology Research Institute and the Naval Dosimetry Center, was designed. This network based on the use of multiple biodosimetry modalities would provide diagnostic and triage capabilities needed to meet USDOD requirements. These are not available with sufficient capacity elsewhere but could be needed urgently after a major radiological/nuclear event.

Contrast-detail phantom scoring methodology.

Published results of medical imaging studies which make use of contrast detail mammography (CDMAM) phantom images for analysis are difficult to compare since data are often not analyzed in the same way. In order to address this situation, the concept of ideal contrast detail curves is suggested. The ideal contrast detail curves are constructed based on the requirement of having the same product of the diameter and contrast (disk thickness) of the minimal correctly determined object for every row of the CDMAM phantom image. A correlation and comparison of five different quality parameters of the CDMAM phantom image determined for obtained ideal contrast detail curves is performed. The image quality parameters compared include: (1) contrast detail curve--a graph correlation between "minimal correct reading" diameter and disk thickness; (2) correct observation ratio--the ratio of the number of correctly identified objects to the actual total number of objects multiplied by 100; (3) image quality figure--the sum of the product of the diameter of the smallest scored object and its relative contrast; (4) figure-of-merit--the zero disk diameter value obtained from extrapolation of the contrast detail curve to the origin (e.g., zero disk diameter); and (5) k-factor--the product of the thickness and the diameter of the smallest correctly identified disks. The analysis carried out showed the existence of a nonlinear relationship between the above parameters, which means that use of different parameters of CDMAM image quality potentially can cause different conclusions about changes in image quality. Construction of the ideal contrast detail curves for CDMAM phantom is an attempt to determine the quantitative limits of the CDMAM phantom as employed for image quality evaluation. These limits are determined by the relationship between certain parameters of a digital mammography system and the set of the gold disks sizes in the CDMAM phantom. Recommendations are made on selections of CDMAM phantom regions which should be used for scoring at different image quality and which scoring methodology may be most appropriate. Special attention is also paid to the use of the CDMAM phantom for image quality assessment of digital mammography systems particularly in the vicinity of the Nyquist frequency.

X-Band Rapid-Scan Electron Paramagnetic Resonance of Radiation-Induced Defects in Tooth Enamel.

X-band rapid-scan electron paramagnetic resonance (EPR) spectra from tooth enamel samples irradiated with doses of 0.5, 1 and 10 Gy had substantially improved signal-to-noise relative to conventional continuous wave EPR. The radiation-induced signal in a 60 mg of a tooth enamel sample irradiated with a 0.5 Gy dose was readily characterized in spectra recorded with 34 min data acquisition times. The coefficient of variance of the calculated dose for a 1 Gy irradiated sample, based on simulation of the first-derivative spectra for three replicates as the sum of native and radiation-induced signals, was 3.9% for continuous wave and 0.4% for rapid scan.

The high dose response and functional capability of the DT-702/Pd lithium fluoride thermoluminescent dosimeter.

The United States Navy monitors the dose its radiation workers receive using the DT-702/PD thermoluminescent dosimeter, which consists of the Harshaw 8840 holder and the four-element Harshaw 8841 card. There were two main objectives of this research. In the first objective, the dosimeters were exposed to 100 Gy using electron and x-ray beams and found to respond approximately 30-40% lower than the delivered dose. No significant effect on the under-response was found when dose rate, radiation type, dosimeter position on the phantom, and dosimeter material were varied or when the card was irradiated while enclosed in its holder. Since the current naval policy is to remove from occupational use any thermoluminescent dosimeter with an accumulated deep dose equivalent of 0.05 Sv or greater, the functionality of the dosimeter was also investigated at deep dose equivalents of 0.05, 0.15, and 0.25 Sv using 60Co and 137Cs sources as the second main objective. All dosimeters were annealed following exposure and then exposed to 5.0 mSv from a 90Sr source. In all cases, the dosimeters responded within 3% of the delivered dose, indicating that the dosimeters remained functional as defined by naval dosimetry requirements. However, the anneal time required to clear the thermoluminescent dosimeter's reading was found to increase approximately as the cube root with the delivered dose.

Mapping the distribution of (90)Sr in teeth with a photostimulable phosphor imaging detector.

The present communication describes the technical aspects of the first application of an imaging plate for visualization of (90)Sr deposited in human teeth. The teeth were obtained from Techa River area residents who were exposed as a result of releases of radioactivity into the Techa River by the first Soviet nuclear plant Mayak in the early 1950s. The investigations form the basis for an experimental procedure for accurate mapping of the distribution of (90)Sr in teeth with an imaging plate. This new method can be used as an individual indicator of radionuclide intake. Its advantages are its high sensitivity (0.02 Bq/g mm(-2) of (90)Sr), it ability to examine small detectable cross-sectional areas of dental tissue (dentin) contaminated with (90)Sr (from 0.01 mm(2)), the nondestructive method of analysis, and the simplicity of use. The combined application of this method with EPR tooth biodosimetry can provide more accurate dose reconstruction and may lead to more effective radiation risk assessment.

Study of the stability of EPR signals after irradiation of fingernail samples.

Previous studies have suggested that the electron paramagnetic resonance in fingernails can be used for radiation dosimetry purposes. Use of fingernails as an emergency dosimeter has benefits of easy, noninvasive sampling and fast dose measurements (∼10 min) potentially in field conditions and almost immediately after an exposure event. This study represents the next step in the development of EPR fingernail dosimetry; e.g., evaluation of the stability of the radiation-induced signal (RIS) at different storage and irradiation conditions. RIS fading during storage in both stressed (untreated) and unstressed (soaked in water) samples (n = 20) was studied at two temperature conditions: freezing (temp ≈ -20°C) and room temperature (20-24°C). Fingernail samples with the same clipping size and number and irradiated to 15 and 20 Gy were measured for over 200 d. Those irradiated to 100 and 200 Gy were measured for 114 d. The other group of samples irradiated to 1, 3, 8, and 20 Gy was followed for 25 mo of storage time. This study demonstrated that all samples that were kept at low freezing temperatures showed a stable RIS with no significant fading. All samples that were kept at room temperatures showed an initial fading of the signal with a slow rise of the EPR signal after irradiation with time to a saturation level. Obtained results allow making recommendations on the appropriate storage conditions of fingernails for EPR dosimetry use.

Impact of the Fukushima nuclear accident on background radiation doses measured by control dosimeters in Japan.

After the 9.0 magnitude earthquake and subsequent massive tsunami on 11 March 2011 in Japan, several reactors at the Fukushima Daiichi Nuclear Power Plant suffered severe damage. There was immediate participation of U.S. Navy vessels and other United States Department of Defense (DoD) teams that were already in the area at the time of the disaster or arrived shortly thereafter. The correct determination of occupational dose equivalent requires estimation of the background dose component measured by control dosimeters, which is subsequently subtracted from the total dose equivalent measured by personal dosimeters. The purpose of the control dosimeters is to determine the amount of radiation dose equivalent that has accumulated on the dosimeter from background or other non-occupational sources while they are in transit or being stored. Given the release of radioactive material and potential exposure to radiation from the Fukushima Daiichi Nuclear Power Plant and the process by which the U.S. Navy calculates occupational exposure to ionizing radiation, analysis of pre- and post-event control dosimeters is warranted. Several hundred historical dose records from the Naval Dosimetry Center (NDC) database were analyzed and compared with the post-accident dose equivalent data of control dosimeters. As result, it was shown that the dose contribution of the radiation and released radiological materials from the Fukushima nuclear accident to background radiation doses is less than 0.375 µSv d for shallow and deep photon dose equivalent. There is no measurable effect on neutron background exposure. The latter has at least two important conclusions. First, the NDC can use doses measured by control dosimeters at issuing sites in Japan for determination of personnel dose equivalents; second, the dose data from control dosimeters prior to and after the Fukushima accident may be used to assist in dose reconstruction of non-radiological (non-badged) personnel at these locations.

90Sr in mammal teeth from contaminated areas in the former Soviet Union measured by imaging plates.

Imaging plates sensitive to beta rays were used to obtain the images of 90Sr in tooth samples taken from mammals collected in contaminated areas of the former Soviet Union. The average concentrations of 90Sr in the samples were determined by comparing the intensities of the luminescence using a single crystal of KCl. The results showed that the determined 90Sr concentration has a positive correlation with the soil contamination levels in the South Ural region. Tooth samples from both inside of the Semipalatinsk nuclear test site and the villages nearby have detectable amounts of 90Sr, indicating the possible presence of residual soil contamination. The present study demonstrates that using imaging plates is a very sensitive method to detect 90Sr in teeth as well as to estimate low-level 90Sr contamination in soil.

Synopsis of partial-body radiation diagnostic biomarkers and medical management of radiation injury workshop.

Radiation exposures from accidents, nuclear detonations or terrorist incidents are unlikely to be homogeneous; however, current biodosimetric approaches are developed and validated primarily in whole-body irradiation models. A workshop was held at the Armed Forces Radiobiology Research Institute in May 2008 to draw attention to the need for partial-body biodosimetry, to discuss current knowledge, and to identify the gaps to be filled. A panel of international experts and the workshop attendees discussed the requirements and concepts for a path forward. This report addresses eight key areas identified by the Workshop Program Committee for future focus: (1) improved cytogenetics, (2) clinical signs and symptoms, (3) cutaneous bioindicators, (4) organ-specific biomarkers, (5) biophysical markers of dose, (6) integrated diagnostic approaches, (7) confounding factors, and (8) requirements for post-event medical follow-up. For each area, the status, advantages and limitations of existing approaches and suggestions for new directions are presented.