Development of in vivo tooth EPR for individual radiation dose estimation and screening

In Vivo Verification of Electron Paramagnetic Resonance Biodosimetry Using Patients Undergoing Radiation Therapy Treatment

PURPOSE

Electron paramagnetic resonance (EPR) biodosimetry, used to triage large numbers of individuals incidentally exposed to unknown doses of ionizing radiation, is based on detecting a stable physical response in the body that is subject to quantifiable variation after exposure. In vivo measurement is essential to fully characterize the radiation response relevant to a living tooth measured in situ. The purpose of this study was to verify EPR spectroscopy in vivo by estimating the radiation dose received in participants' teeth.

METHODS AND MATERIALS

A continuous wave L-band spectrometer was used for EPR measurements. Participants included healthy volunteers and patients undergoing head and neck and total body irradiation treatments. Healthy volunteers completed 1 measurement each, and patients underwent measurement before starting treatment and between subsequent fractions. Optically stimulated luminescent dosimeters and diodes were used to determine the dose delivered to the teeth to validate EPR measurements.

RESULTS

Seventy measurements were acquired from 4 total body irradiation and 6 head and neck patients over 15 months. Patient data showed a linear increase of EPR signal with delivered dose across the dose range tested. A linear least-squares weighted fit of the data gave a statistically significant correlation between EPR signal and absorbed dose (P < .0001). The standard error of inverse prediction (SEIP), used to assess the usefulness of fits, was 1.92 Gy for the dose range most relevant for immediate triage (≤7 Gy). Correcting for natural background radiation based on patient age reduced the SEIP to 1.51 Gy.

CONCLUSIONS

This study demonstrated the feasibility of using spectroscopic measurements from radiation therapy patients to validate in vivo EPR biodosimetry. The data illustrated a statistically significant correlation between the magnitude of EPR signals and absorbed dose. The SEIP of 1.51 Gy, obtained under clinical conditions, indicates the potential value of this technique in response to large radiation events.

Electron Paramagnetic Resonance (EPR) Biodosimetry with Human Teeth: A Crucial Technique for Acute and Chronic Exposure Assessment

ABSTRACT

Radiation exposure is a primary concern in emergency response scenarios and long-term health assessments. Accurate quantification of radiation doses is critical for informed decision-making and patient care. This paper reviews the dose reconstruction technique using both X- and Q-bands, with tooth enamel as a reliable dosimeter. Tooth enamel, due to its exceptional resistance to alteration over time, offers a unique opportunity for assessing both acute and chronic radiation exposures. This review delves into the principles underlying enamel dosimetry, the mechanism of radiation interactions, and dose retention in tooth enamel. We explore state-of-the-art analytical methods, such as electron paramagnetic resonance (EPR) spectroscopy, that accurately estimate low and high doses in acute and chronic exposure. Furthermore, we discuss the applicability of tooth enamel dosimetry in various scenarios, ranging from historical radiological incidents to recent nuclear events or radiological incidents. The ability to reconstruct radiation doses from dental enamel provides a valuable tool for epidemiological studies, validating the assessment of health risks associated with chronic exposures and aiding in the early detection and management of acute radiation incidents. This paper underscores the significance of tooth enamel as an essential medium for radiation dose reconstruction and its broader implications for enhancing radiation protection, emergency response, and public health preparedness. Incorporating enamel EPR dosimetry into standard protocols has the potential to transform the field of radiation assessment, ensuring more accurate and timely evaluations of radiation exposure and its associated risks.

Enhancing Precision in L-band Electron Paramagnetic Resonance Tooth Dosimetry: Incorporating Digital Image Processing and Radiation Therapy Plans for Geometric Correction

ABSTRACT

Following unforeseen exposure to radiation, quick dose determination is essential to prioritize potential patients that require immediate medical care. L-band electron paramagnetic resonance tooth dosimetry can be efficiently used for rapid triage as this poses no harm to the human incisor, although geometric variations among human teeth may hinder accurate dose estimation. Consequently, we propose a practical geometric correction method using a mobile phone camera. Donated human incisors were irradiated with calibrated 6-MV photon beam irradiation, and dose-response curves were developed by irradiation with a predetermined dose using custom-made poly(methyl methacrylate) slab phantoms. Three radiation treatment plans for incisors were selected and altered to suit the head phantom. The mean doses on tooth structures were calculated using a commercial treatment planning system, and the electron paramagnetic resonance signals of the incisors were measured. The enamel area was computed from camera-acquired tooth images. The relative standard uncertainty was rigorously estimated both with and without geometric correction. The effects on the electron paramagnetic resonance signal caused by axial and rotational movements of tooth samples were evaluated through finite element analysis. The mean absolute deviations of mean doses both with and without geometric correction showed marginal improvement. The average relative differences without and with geometric correction significantly decreased from 21.0% to 16.8% (p = 0.01). The geometric correction method shows potential in improving dose precision measurement with minimal delay. Furthermore, our findings demonstrated the viability of using treatment planning system doses in dose estimation for L-band electron paramagnetic resonance tooth dosimetry.

EPR biodosimetry: challenges and opportunities

This paper briefly examines electron paramagnetic resonance (EPR) techniques to measure dose from exposure to external radiation, assessing their current status, potential future uses and the challenges impacting their progress. We conclude the uses and potential value of different EPR techniques depend on the number of victims and whether they characterize short- or long-term risks from exposure. For large populations, EPR biodosimetry based on in vivo measurements or using co-located inanimate objects offer the greatest promise for assessing acute, life-threatening risk and the magnitude and extent of such risk. To assess long-term risk, ex vivo EPR methods using concentrated enamel from exfoliated teeth are most impactful. For small groups, ex vivo EPR biodosimetry based on available samples of teeth, nails and/or bones are most useful. The most important challenges are common to all approaches: improve the technique's technical capabilities and advance recognition by planning groups of the relative strengths EPR techniques offer for each population size. The most useful applications are likely to be for triage and medical guidance in large events and for radiation epidemiology to evaluate long-term risks.

Frequency-fixed motion compensation system for in-vivo electron paramagnetic resonance tooth dosimetry

This article describes the design process for a motion compensation system that can suppress the spectral distortion caused by human motion and breathing during in-vivo electron paramagnetic resonance (EPR) spectroscopy on an intact incisor. The developed system consists of two elements: an electronically controlled tunable resonator and an automatic control circuit (ACC). The resonator can modify the resonant frequency and impedance by tuning and matching the voltage, while the ACC can generate a feedback signal using phase-sensitive detection (PSD). The signal is transferred into the resonator to maintain the critical coupling state. The tunable frequency range of the resonator was measured at over 10 MHz, offering approximately eight times the required range. The bandwidth of the resonator fluctuated in a negligible range (0.14% relative standard error) following the resonant frequency. With the feedback signal on, in-vivo EPR measurements were demonstrated to be a stable baseline with 35% higher signal-to-noise ratio (SNR). When one incisor sample was irradiated by an X-ray instrument, the EPR signal responses to the absorbed doses of 0-10 Gy exhibited high linearity (R2 = 0.994). In addition, the standard error of inverse prediction was estimated to be 0.35 Gy. The developed system achieved a discrimination ability of 2 Gy, which is required for triage in large-scale radiation accidents. Moreover, the compensation is fully automated, meaning that the system can be operated with simple training in an emergency.

Dependence of Radiation-induced Signals on Geometry of Tooth Enamel Using a 1.15 GHz Electron Paramagnetic Resonance Spectrometer: Improvement of Dosimetric Accuracy

ABSTRACT

We aim to improve the accuracy of electron paramagnetic resonance (EPR)-based in vivo tooth dosimetry using the relationship between tooth geometry and radiation-induced signals (RIS). A homebuilt EPR spectrometer at L-band frequency of 1.15 GHz originally designed for non-invasive and in vivo measurements of intact teeth was used to measure the RIS of extracted human teeth. Twenty human central incisors were scanned by microCT and irradiated by 220 kVp x-rays. The RISs of the samples were measured by the EPR spectrometer as well as simulated by using the finite element analysis of the electromagnetic field. A linear relationship between simulated RISs and tooth geometric dimensions, such as enamel area, enamel volume, and labial enamel volume, was confirmed. The dose sensitivity was quantified as a slope of the calibration curve (i.e., RIS vs. dose) for each tooth sample. The linear regression of these dose sensitivities was established for each of three tooth geometric dimensions. Based on these findings, a method for the geometry correction was developed by use of expected dose sensitivity of a certain tooth for one of the tooth geometric dimensions. Using upper incisors, the mean absolute deviation (MAD) without correction was 1.48 Gy from an estimated dose of 10 Gy; however, the MAD corrected by enamel area, volume, and labial volume was reduced to 1.04 Gy, 0.77 Gy, and 0.83 Gy, respectively. In general, the method corrected by enamel volume showed the best accuracy in this study. This homebuilt EPR spectrometer for the purpose of non-invasive and in vivo tooth dosimetry was successfully tested for achieving measurements in situ. We demonstrated that the developed correction method could reduce dosimetric uncertainties resulting from the variations in tooth geometric dimensions.

A normalization method of the volume and geometry of tooth for X-band in vivo EPR dosimetry

The accuracy of in vivo EPR tooth dosimetry may be influenced by the volume and geometry variations in teeth, especially when there is considerable non-uniform sensitivity distribution in the active detection area of the cavity. To solve this problem, the present research proposed a normalization method specifically for X-band EPR in vivo tooth dosimetry. The volume and geometry of the measured tooth were reconstructed by digital image processing with images of the tooth impression slices, which were obtained by a custom-made impression module. The sensitivity distribution in the active detection area was established based on experiments with a point sample. Consequently, a composite normalization process that could calibrate the evaluated dose effectively was carried out by taking into account the influences not only from tooth volume and geometry but also from the non-uniform distribution of sensitivity. The effect and practicability of the method were evaluated by incisor samples. Results showed that the standard deviation could be reduced a maximum of 54.8% approximately after the composite normalization, an improvement compared to results from solely tooth volume. The correlation coefficient of the dose-response curve could be improved from 0.731 to 0.986. The preliminary method provides an approach potentially useful on site after radiation accidents when dealing with the influence of variations in the tooth volume and geometry for X-band EPR in vivo dose estimations.

In Vivo Electron Paramagnetic Resonance Tooth Dosimetry: Dependence of Radiation-Induced Signal Amplitude on the Enamel Thickness and Surface Area of Ex Vivo Human Teeth

In vivo L-band electron paramagnetic resonance tooth dosimetry is a newly developed and very promising method for retrospective biodosimetry in individuals who may have been exposed to significant levels of ionizing radiation. The present study aimed to determine the relationships among enamel thickness, enamel area, and measured electron paramagnetic resonance signal amplitude with a view to improve the quantitative accuracy of the dosimetry technique. Ten isolated incisors were irradiated using well-characterized doses, and their radiation-induced electron paramagnetic resonance signals were measured. Following the measurements, the enamel thickness and area of each tooth were measured using micro-focus computed tomography. Linear regression showed that the enamel area at each measurement position significantly affected the radiation-induced electron paramagnetic resonance signal amplitude (p < 0.001). Simulation data agreed well with this result. These results indicate that it is essential to properly consider enamel thickness and area when interpreting electron paramagnetic resonance tooth dosimetry measurements to optimize the accuracy of dose estimation.

IN-VIVO RADIATION DOSIMETRY USING PORTABLE L BAND EPR: ON-SITE MEASUREMENT OF VOLUNTEERS IN FUKUSHIMA PREFECTURE, JAPAN

The aim of this study was to make direct measurements of the possible radiation-induced EPR signals in the teeth of volunteers who were residents in Fukushima within 80 km distance from the Fukushima Nuclear Power plant at the time of the disaster, and continued to live there for at least 3 month after the disaster. Thirty four volunteers were enrolled in this study. These measurements were made using a portable L-band EPR spectrometer, which was originally developed in the EPR Center at Dartmouth. All measurements were performed using surface loop resonators that have been specifically designed for the upper incisor teeth. Potentially these signals include not only radiation-induced signals induced by the incident but also background signals including those from prior radiation exposure from the environment and medical exposure. We demonstrated that it is feasible to transport the dosimeter to the measurement site and make valid measurements. The intensity of the signals that were obtained was not significantly above those seen in volunteers who had not had potential radiation exposures at Fukushima.

Evolution and Optimization of Tooth Models for Testing In Vivo EPR Tooth Dosimetry

Testing and verification are an integral part of any cycle to design, manufacture and improve a novel device intended for use in humans. In the case of testing Dartmouth's electron paramagnetic resonance (EPR) in vivo tooth dosimetry device, in vitro studies are needed throughout its development to test its performance, i.e. to verify its current capability for assessing dose in individuals potentially exposed to ionizing radiation. Since the EPR device uses the enamel of human teeth to assess dose, models that include human teeth have been an integral mechanism to carry out in vitro studies during development and testing its ability to meet performance standards for its ultimate intended in vivo use. As the instrument improves over time, new demands for in vitro studies change as well. This paper describes the tooth models used to perform in vitro studies and their evolution to meet the changing demands for testing in vivo EPR tooth dosimetry.

The Application and Distribution of Magnetic Field Modulation in the Detection Apertures of X-band EPR Cavities for In Vivo Tooth Dosimetry

In vivo electron paramagnetic resonance tooth dosimetry could be a practical and ideal tool for quick mass triage of victims in the rescue following a disaster event involving irradiation radiation. Magnetic field modulation is an important issue to improve the sensitivity of X-band in vivo tooth dosimetry. We designed a couple of trapezoidal modulation coil sets fixed on the magnet poles that could be used to apply sufficient magnet field modulation into the detection aperture of the resonant cavity. Measurements of irradiated teeth with such coil sets demonstrated significant radiation-induced signals. The modulation generation efficiencies and magnetic field distributions in apertures with different cavity geometries were analytically calculated, simulated by a finite element method and evaluated by measurements of a free radical point sample to study the influences caused by the geometries of the apertures and other factors.

Contribution of Harold M. Swartz to In Vivo EPR and EPR Dosimetry

In 2015, we are celebrating half a century of research in the application of Electron Paramagnetic Resonance (EPR) as a biodosimetry tool to evaluate the dose received by irradiated people. During the EPR Biodose 2015 meeting, a special session was organized to acknowledge the pioneering contribution of Harold M. (Hal) Swartz in the field. The article summarizes his main contribution in physiology and medicine. Four emerging themes have been pursued continuously along his career since its beginning: (1) radiation biology; (2) oxygen and oxidation; (3) measuring physiology in vivo; and (4) application of these measurements in clinical medicine. The common feature among all these different subjects has been the use of magnetic resonance techniques, especially EPR. In this article, you will find an impressionist portrait of Hal Swartz with the description of the 'making of' this pioneer, a time-line perspective on his career with the creation of three National Institutes of Health-funded EPR centers, a topic-oriented perspective on his career with a description of his major contributions to Science, his role as a mentor and his influence on his academic children, his active role as founder of scientific societies and organizer of scientific meetings, and the well-deserved international recognition received so far.

Tooth Retrospective Dosimetry Using Electron Paramagnetic Resonance: Influence of Irradiated Dental Composites

In the aftermath of a major radiological accident, the medical management of overexposed individuals will rely on the determination of the dose of ionizing radiations absorbed by the victims. Because people in the general population do not possess conventional dosimeters, after the fact dose reconstruction methods are needed. Free radicals are induced by radiations in the tooth enamel of victims, in direct proportion to dose, and can be quantified using Electron Paramagnetic Resonance (EPR) spectrometry, a technique that was demonstrated to be very appropriate for mass triage. The presence of dimethacrylate based restorations on teeth can interfere with the dosimetric signal from the enamel, as free radicals could also be induced in the various composites used. The aim of the present study was to screen irradiated composites for a possible radiation-induced EPR signal, to characterize it, and evaluate a possible interference with the dosimetric signal of the enamel. We investigated the most common commercial composites, and experimental compositions, for a possible class effect. The effect of the dose was studied between 10 Gy and 100 Gy using high sensitivity X-band spectrometer. The influence of this radiation-induced signal from the composite on the dosimetric signal of the enamel was also investigated using a clinical L-Band EPR spectrometer, specifically developed in the EPR center at Dartmouth College. In X-band, a radiation-induced signal was observed for high doses (25-100 Gy); it was rapidly decaying, and not detected after only 24h post irradiation. At 10 Gy, the signal was in most cases not measurable in the commercial composites tested, with the exception of 3 composites showing a significant intensity. In L-band study, only one irradiated commercial composite influenced significantly the dosimetric signal of the tooth, with an overestimation about 30%. In conclusion, the presence of the radiation-induced signal from dental composites should not significantly influence the dosimetry for early dose assessment.

A proposed method for retrospective eye dose assessments for the purposes of resolving cataract compensation claims

The 2011 International Commission on Radiological Protection (ICRP) statement on tissue reactions suggested a significant reduction in the threshold dose for radiation induced cataracts. This, combined with the potential for a long delay between exposure and cataract diagnosis, may result in an increased requirement to evaluate eye dose from past exposures in order to settle current compensation claims. This article highlights how compensation claims relating to radiation exposure are assessed within the UK legal system and suggests that in vivo Electro Paramagnetic Resonance (EPR) dosimetry of teeth has utility for the retrospective quantification of radiation doses to the eye. It was identified that in vivo EPR in its current form may be sufficiently sensitive to support cataract compensation claims, although further work is required to enable appropriate dose conversion coefficients to be quantified.

New developed cylindrical TM010 mode EPR cavity for X-band in vivo tooth dosimetry

EPR tooth in vivo dosimetry is an attractive approach for initial triage after unexpected nuclear events. An X-band cylindrical TM010 mode resonant cavity was developed for in vivo tooth dosimetry and used in EPR applications for the first time. The cavity had a trapezoidal measuring aperture at the exact position of the cavity's cylindrical wall where strong microwave magnetic field H1 concentrated and weak microwave electric field E1 distributed. Theoretical calculations and simulations were used to design and optimize the cavity parameters. The cavity features were evaluated by measuring DPPH sample, intact incisor samples embed in a gum model and the rhesus monkey teeth. The results showed that the cavity worked at designed frequency and had the ability to make EPR spectroscopy in relative high sensitivity. Sufficient modulation amplitude and microwave power could be applied into the aperture. Radiation induced EPR signal could be observed remarkably from 1 Gy irradiated intact incisor within only 30 seconds, which was among the best in scan time and detection limit. The in vivo spectroscopy was also realized by acquiring the radiation induced EPR signal from teeth of rhesus monkey whose teeth was irradiated by dose of 2 Gy. The results suggested that the cavity was sensitive to meet the demand to assess doses of significant level in short time. This cavity provided a very potential option for the development of X-band in vivo dosimetry.

2013 Dade W. Moeller lecture: medical countermeasures against radiological terrorism

Soon after the 9-11 attacks, politicians and scientists began to question our ability to cope with a large-scale radiological terrorism incident. The outline of what was needed was fairly obvious: the ability to prevent such an attack, methods to cope with the medical consequences, the ability to clean up afterward, and the tools to figure out who perpetrated the attack and bring them to justice. The medical response needed three components: the technology to determine rapidly the radiation doses received by a large number of people, methods for alleviating acute hematological radiation injuries, and therapies for mitigation and treatment of chronic radiation injuries. Research done to date has shown that a realistic medical response plan is scientifically possible, but the regulatory and financial barriers to achieving this may currently be insurmountable.

Development and validation of an ex vivo electron paramagnetic resonance fingernail biodosimetric method

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.

Clinical EPR: unique opportunities and some challenges

Electron paramagnetic resonance (EPR) spectroscopy has been well established as a viable technique for measurement of free radicals and oxygen in biological systems, from in vitro cellular systems to in vivo small animal models of disease. However, the use of EPR in human subjects in the clinical setting, although attractive for a variety of important applications such as oxygen measurement, is challenged with several factors including the need for instrumentation customized for human subjects, probe, and regulatory constraints. This article describes the rationale and development of the first clinical EPR systems for two important clinical applications, namely, measurement of tissue oxygen (oximetry) and radiation dose (dosimetry) in humans. The clinical spectrometers operate at 1.2 GHz frequency and use surface-loop resonators capable of providing topical measurements up to 1 cm depth in tissues. Tissue pO2 measurements can be carried out noninvasively and repeatedly after placement of an oxygen-sensitive paramagnetic material (currently India ink) at the site of interest. Our EPR dosimetry system is capable of measuring radiation-induced free radicals in the tooth of irradiated human subjects to determine the exposure dose. These developments offer potential opportunities for clinical dosimetry and oximetry, which include guiding therapy for individual patients with tumors or vascular disease by monitoring of tissue oxygenation. Further work is in progress to translate this unique technology to routine clinical practice.

Assessment of biodosimetry methods for a mass-casualty radiological incident: medical response and management considerations

Following a mass-casualty nuclear disaster, effective medical triage has the potential to save tens of thousands of lives. In order to best use the available scarce resources, there is an urgent need for biodosimetry tools to determine an individual's radiation dose. Initial triage for radiation exposure will include location during the incident, symptoms, and physical examination. Stepwise triage will include point of care assessment of less than or greater than 2 Gy, followed by secondary assessment, possibly with high throughput screening, to further define an individual's dose. Given the multisystem nature of radiation injury, it is unlikely that any single biodosimetry assay can be used as a standalone tool to meet the surge in capacity with the timeliness and accuracy needed. As part of the national preparedness and planning for a nuclear or radiological incident, the authors reviewed the primary literature to determine the capabilities and limitations of a number of biodosimetry assays currently available or under development for use in the initial and secondary triage of patients. Understanding the requirements from a response standpoint and the capability and logistics for the various assays will help inform future biodosimetry technology development and acquisition. Factors considered include: type of sample required, dose detection limit, time interval when the assay is feasible biologically, time for sample preparation and analysis, ease of use, logistical requirements, potential throughput, point-of-care capability, and the ability to support patient diagnosis and treatment within a therapeutically relevant time point.

A Deployable In Vivo EPR Tooth Dosimeter for Triage After a Radiation Event Involving Large Populations

In order to meet the potential need for emergency large-scale retrospective radiation biodosimetry following an accident or attack, we have developed instrumentation and methodology for in vivo electron paramagnetic resonance spectroscopy to quantify concentrations of radiation-induced radicals within intact teeth. This technique has several very desirable characteristics for triage, including independence from confounding biologic factors, a non-invasive measurement procedure, the capability to make measurements at any time after the event, suitability for use by non-expert operators at the site of an event, and the ability to provide immediate estimates of individual doses. Throughout development there has been a particular focus on the need for a deployable system, including instrumental requirements for transport and field use, the need for high throughput, and use by minimally trained operators.Numerous measurements have been performed using this system in clinical and other non-laboratory settings, including in vivo measurements with unexposed populations as well as patients undergoing radiation therapies. The collection and analyses of sets of three serially-acquired spectra with independent placements of the resonator, in a data collection process lasting approximately five minutes, provides dose estimates with standard errors of prediction of approximately 1 Gy. As an example, measurements were performed on incisor teeth of subjects who had either received no irradiation or 2 Gy total body irradiation for prior bone marrow transplantation; this exercise provided a direct and challenging test of our capability to identify subjects who would be in need of acute medical care.

A Framework for Comparative Evaluation of Dosimetric Methods to Triage a Large Population Following a Radiological Event

BACKGROUND: To prepare for a possible major radiation disaster involving large numbers of potentially exposed people, it is important to be able to rapidly and accurately triage people for treatment or not, factoring in the likely conditions and available resources. To date, planners have had to create guidelines for triage based on methods for estimating dose that are clinically available and which use evidence extrapolated from unrelated conditions. Current guidelines consequently focus on measuring clinical symptoms (e.g., time-to-vomiting), which may not be subject to the same verification of standard methods and validation processes required for governmental approval processes of new and modified procedures. Biodosimeters under development have not yet been formally approved for this use. Neither set of methods has been tested in settings involving large-scale populations at risk for exposure. OBJECTIVE: To propose a framework for comparative evaluation of methods for such triage and to evaluate biodosimetric methods that are currently recommended and new methods as they are developed. METHODS: We adapt the NIH model of scientific evaluations and sciences needed for effective translational research to apply to biodosimetry for triaging very large populations following a radiation event. We detail criteria for translating basic science about dosimetry into effective multi-stage triage of large populations and illustrate it by analyzing 3 current guidelines and 3 advanced methods for biodosimetry. CONCLUSIONS: This framework for evaluating dosimetry in large populations is a useful technique to compare the strengths and weaknesses of different dosimetry methods. It can help policy-makers and planners not only to compare the methods' strengths and weaknesses for their intended use but also to develop an integrated approach to maximize their effectiveness. It also reveals weaknesses in methods that would benefit from further research and evaluation.

Prevention of future incidents and investigational lines

All radiation devices in use nowadays are subject to cause serious incidents and accidents, with potential risks in exposed population groups. These risks may have immediate or long term health implications. The detection of radioactive incidents is a procedure that should be systematized in economically developed societies. International organizations may provide support to other states in the event of a radioactive incident. Prevention, mitigation and treatment of the radiation effects are done by anticipating the moment of exposure and by establishing new efforts for investigation of radioprotective products. In this article we will analyze the causes of radiological incidents, the means to detect them, and the current preventive and therapeutic procedures available, with special emphasis on new biodosimetry methods for triage and investigational radioprotective drugs. Finally, we will explore the most efficient measures, for future prevention.

Physically-based biodosimetry using in vivo EPR of teeth in patients undergoing total body irradiation

PURPOSE

The ability to estimate individual exposures to radiation following a large attack or incident has been identified as a necessity for rational and effective emergency medical response. In vivo electron paramagnetic resonance (EPR) spectroscopy of tooth enamel has been developed to meet this need.

MATERIALS AND METHODS

A novel transportable EPR spectrometer, developed to facilitate tooth dosimetry in an emergency response setting, was used to measure upper incisors in a model system, in unirradiated subjects, and in patients who had received total body doses of 2 Gy.

RESULTS

A linear dose response was observed in the model system. A statistically significant increase in the intensity of the radiation-induced EPR signal was observed in irradiated versus unirradiated subjects, with an estimated standard error of dose prediction of 0.9 ± 0.3 Gy.

CONCLUSIONS

These results demonstrate the current ability of in vivo EPR tooth dosimetry to distinguish between subjects who have not been irradiated and those who have received exposures that place them at risk for acute radiation syndrome. Procedural and technical developments to further increase the precision of dose estimation and ensure reliable operation in the emergency setting are underway. With these developments EPR tooth dosimetry is likely to be a valuable resource for triage following potential radiation exposure of a large population.

The view from the trenches: part 1-emergency medical response plans and the need for EPR screening

Few natural disasters or intentional acts of war or terrorism have the potential for such severe impact upon a population and infrastructure as the intentional detonation of a nuclear device within a major U.S. city. In stark contrast to other disasters or even a "dirty bomb," hundreds of thousands will be affected and potentially exposed to a clinically significant dose of ionizing radiation. This will result in immediate deaths and injuries and subsequently the development of Acute Radiation Syndrome (ARS). Additionally, millions more who are unlikely to develop ARS will seek medical evaluation and treatment, overwhelming the capacity of an already compromised medical system. In this paper, the authors propose that in vivo electron paramagnetic resonance (EPR) dosimetry be utilized to screen large numbers of potentially exposed victims, and that this screening process be incorporated into the medical-surge framework that is currently being implemented across the nation for other catastrophic public health emergencies. The National Incident Management System (NIMS), the National Response Framework (NRF), the Target Capabilities List (TCL), Homeland Security Presidential Directives (HSPD), as well as additional guidance from multiple federal agencies provide a solid framework for this response. The effective screening of potentially-exposed victims directly following a nuclear attack could decrease the number of patients seeking immediate medical care by greater than 90%.

The view from the trenches: part 2-technical considerations for EPR screening

There is growing awareness of the need for methodologies that can be used retrospectively to provide the biodosimetry needed to carry out screening and triage immediately after an event in which large numbers of people have potentially received clinically significant doses of ionizing radiation. The general approach to developing such methodologies has been a technology centric one, often ignoring the system integrations considerations that are key to their effective use. In this study an integrative approach for the evaluation and development of a physical biodosimetry technology was applied based on in vivo electron paramagnetic resonance (EPR) dosimetry. The EPR measurements are based on physical changes in tissues whose magnitudes are not affected by the factors that can confound biologically-based assessments. In this study the use of a pilot simulation exercise to evaluate an experimental EPR system and gather stakeholders' feedback early on in the development process is described. The exercise involved: ten non-irradiated participants, representatives from a local fire department; Department of Homeland Security certified exercise evaluators, EPR experts, physicians; and a human factors engineer. Stakeholders were in agreement that the EPR technology in its current state of development could be deployed for the screening of mass casualties. Furthermore, stakeholders' recommendations will be prioritized and incorporated in future developments of the EPR technique. While the results of this exercise were aimed specifically at providing feedback for the development of EPR dosimetry for screening mass casualties, the methods and lessons learned are likely to be applicable to other biodosimetric methods.

A critical assessment of biodosimetry methods for large-scale incidents

Recognition is growing regarding the possibility that terrorism or large-scale accidents could result in potential radiation exposure of hundreds of thousands of people and that the present guidelines for evaluation after such an event are seriously deficient. Therefore, there is a great and urgent need for after-the-fact biodosimetric methods to estimate radiation dose. To accomplish this goal, the dose estimates must be at the individual level, timely, accurate, and plausibly obtained in large-scale disasters. This paper evaluates current biodosimetry methods, focusing on their strengths and weaknesses in estimating human radiation exposure in large-scale disasters at three stages. First, the authors evaluate biodosimetry's ability to determine which individuals did not receive a significant exposure so they can be removed from the acute response system. Second, biodosimetry's capacity to classify those initially assessed as needing further evaluation into treatment-level categories is assessed. Third, we review biodosimetry's ability to guide treatment, both short- and long-term, is reviewed. The authors compare biodosimetric methods that are based on physical vs. biological parameters and evaluate the features of current dosimeters (capacity, speed and ease of getting information, and accuracy) to determine which are most useful in meeting patients' needs at each of the different stages. Results indicate that the biodosimetry methods differ in their applicability to the three different stages, and that combining physical and biological techniques may sometimes be most effective. In conclusion, biodosimetry techniques have different properties, and knowledge of their properties for meeting the different needs for different stages will result in their most effective use in a nuclear disaster mass-casualty event.