Review of retrospective dosimetry techniques for external ionising radiation exposures

Radioactive contamination of southeast Abai oblast, Kazakhstan, from the Chinese nuclear weapons testing program at Lop Nor: an analytical review

Between 1949 and 1962 the Soviet Union performed atmospheric tests of nuclear weapons at the Semipalatinsk nuclear test site (SNTS) in Kazakhstan, resulting in widespread contamination of the surrounding region with radioactive fallout. Settlements in the southeast Abai oblast of Kazakhstan, close to the border with China, are not thought to have received significant fallout from the SNTS. There is, however, evidence that the study area, including Makanchi, Urdzhar and Taskesken villages, was contaminated by atmospheric nuclear tests performed by China at the Lop Nor NTS between 1964 and 1980. We identified the most reliable data indicating contamination from the Lop Nor tests from archive documents. Prompt sampling of soil performed in the area revealed elevated levels of total beta activity in the days and weeks following the Lop Nor tests. The highest activities were recorded following the thermonuclear tests in June 1967 and June 1973. Tooth enamel dosimetry using electron paramagnetic resonance methods suggests residents of the study area have been exposed to excess doses of 50-60 mGy but provides no information on the source and timing of exposure. Currently, evidence of contamination of the study area from nuclear weapons testing at Lop Nor is based on limited radiation measurement data. Therefore, work will continue on the search for archival data on radiological and meteorological monitoring carried out in the study area at the time of the Lop Nor testing campaign.

The effects of age and other individual factors on radiation induced ESR signals from fingernails

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.

Use of optical techniques to evaluate the ionizing radiation effects on biological specimens

Radiation induces various changes in biological specimens; however, the evaluation of these changes is usually complicated and can be achieved only through investment in time and labor. Optical methods reduce the cost of such evaluations as they require less pretreatment of the sample, are adaptable to high-throughput screening and are easy to automate. Optical methods are also advantageous, owing to their real-time and onsite evaluation capabilities. Here, we discuss three optical technologies to evaluate the effects of radiation on biological samples: single-molecule tracking microscopy to evaluate the changes in the physical properties of DNA, Raman spectral microscopy for dosimetry using human hair and second-harmonic generation microscopy to evaluate the effect of radiation on the differentiation of stem cells. These technologies can also be combined for more detailed information and are applicable to other biological samples. Although optical methods are not commonly used to evaluate the effects of radiation, advances in this technology may facilitate the easy and rapid assessment of radiation effects on biological samples.

Cross-species conserved miRNA as biomarker of radiation injury over a wide dose range using nonhuman primate model

Multiple accidents in nuclear power plants and the growing concerns about the misuse of radiation exposure in warfare have called for the rapid determination of absorbed radiation doses (RDs). The latest findings about circulating microRNA (miRNAs) using several animal models revealed considerable promises, although translating this knowledge to clinics remains a major challenge. To address this issue, we randomly divided 36 nonhuman primates (NHPs) into six groups and exposed these groups to six different radiation doses ranging from 6.0-8.5 Gy in increments of 0.5 Gy. Serum samples were collected pre-irradiation as well as three post-irradiation timepoints, namely 1, 2 and 6 days post-total body irradiation (TBI). Generated from a deep sequencing platform, the miRNA reads were multi-variate analyzed to find the differentially expressed putative biomarkers that were linked to RDs, time since irradiation (TSI) and sex. To increase these biomarkers' translational potential, we aligned the NHP-miRNAs' sequences and their functional responses to humans following an in-silico routine. Those miRNAs, which were sequentially and functionally conserved between NHPs and humans, were down selected for further analysis. A linear regression model identified miRNA markers that were consistently regulated with increasing RD but independent TSI. Likewise, a set of potential TSI-markers were identified that consistently shifted with increasing TSI, but independent of RD. Additional molecular analysis found a considerable gender bias in the low-ranges of doses when the risk to radiation-induced fatality was low. Bionetworks linked to cell quantity and cell invasion were significantly altered between the survivors and decedents. Using these biomarkers, an assay could be developed to retrospectively determine the RD and TSI with high translational potential. Ultimately, this knowledge can lead to precise and personalized medicine.

Exploring the thermoluminescence characteristics of smartphone screen safety glasses for retrospective dosimetry applications

In clinical settings, standard dosimeters might miss radiation mishaps. Retrospective dosimeters could help to track personnel (such as patients and other staff who don't wear dosimeters) exceeding safe limits and assess long-term exposure trends. This study has investigated key thermoluminescence (TL) dosimetric characteristics, including the glow curve structure, dose-response, energy dependence, sensitivity and fading of various safety glasses that are used as screen protectors of smartphones subjected to photon irradiation. Among the studied glasses, the HD Anti-Peep safety glass for iPhone has been found to exhibit a linear dose-response with a regression coefficient of 99% within the dose range of 2-10 Gy. Moreover, all the safety glasses showed independence with respect to photon energy of 6 MV and 10 MV. The TL glow curves of the samples showed a broad glow peak between 125 °C and 325 °C at 10 Gy. The TL kinetic parameters of the safety glasses were also studied by analyzing the glow curves using the peak shape and initial rise method. The geometric factor (μg) is found to be within the range of 0.43-0.53, which indicates the suitability of applying Chen's general-order formula to calculate the kinetic parameters such as activation energy, frequency factor and trap lifetime. The activation energy (E) and frequency factor (s) are found in the range of 0.31-0.54 eV and 4.55 × 103 to 2.12 × 106 s-1 respectively obtained via the peak shape method. The relatively long trap lifetime and observed thermoluminescence features indicate that the HD Anti-Peep safety glass offers a better option to estimate dose retrospectively to ensure the safety of human health.

Local environment in yeast-based impedance biodosimeters strongly influences the measurable dose

This work investigates the feasibility of yeast-based impedance measurements for retrospective dosimetry applications. The local environment around yeast cells in a previously developed film-badge was modeled using Geant4. A greater dose response was observed when yeast cells were surrounded by an aluminum-polymer structure, which acted as a conversion layer. Bench-top experiments were conducted using a jar-based dosimeter design that directly combined a finely-ground aluminum conversion medium with yeast powder. It was shown when irradiated in the presence of aluminum grains, yeast cells yielded a higher impedance signal, thereby indicating greater radiation-induced damage. Finally, in separate irradiation experiments, lead and aluminum sheets were placed behind yeast samples and the dosimeters were irradiated to 1 Gy. A 2-fold increase in the impedance signal was shown when samples were positioned in close contact with the lead sheet compared to the aluminum sheet. In all experiments, it was shown that the local environment significantly influences radiative energy deposition in yeast cells.

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.

Saccharomyces Cerevisiae as a Model Organism for Retrospective Impedance Biodosimetry

ABSTRACT

Previous studies have shown that measuring changes in electrical impedance that follow radiation-induced suppression of metabolic activity in irradiated yeast cells can be used to determine radiation dose. The current work investigates the radiation response of Saccharomyces cerevisiae cells by using metabolic activity of cells as a damage indicator. Impedance biodosimetry was examined as a method to evaluate the radiation response of yeast cells. Active lab-grade dry yeast cells were used as the biological material as these samples are simple to handle and have a long shelf-life. A novel dosimeter design has been developed with a strict fabrication method and measurement procedure to ensure reproducible measurements are possible. Prepared yeast samples were irradiated to doses from 0.5 to 8 Gy using a 137Cs source, and a dose response curve was developed that showed a linear relationship of dose with changes in impedance measurements. Fading of the impedance signal was also investigated, and it was shown that there was no noticeable fading of the impedance signal over a period of 7 mo. Finally, the lowest detectable limit measured using this methodology was determined to be 300 mGy. This work presents an alternative retrospective dosimetry technique that can be used at a high scale and low cost following large-scale radiological accidents.

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.

A comprehensive review of dose limits, triage systems and measurement tools for consequence management of nuclear and radiological emergencies

During a radiological or nuclear emergency, occupational workers, members of the public, and emergency responders may be exposed to radionuclides, whether external or internal, through inhalation, ingestion, or wounds. In the case of internalized radiation exposure, prompt assessment of contamination is necessary to inform subsequent medical interventions. This review assembles the constituent considerations for managing nuclear and radiological incidents, focused on a parallel analysis of the evolution of radiation dose limits - notably in the emergency preparedness and response realm - alongside a discussion of triage systems and in vivo radionuclide detection tools. The review maps the development of international and national standards and regulations concerning radiation dose limits, illuminating how past incidents and accumulated knowledge have informed present emergency preparedness and response practices, specifically for internalized radiation. Additionally, the objectives and levels of radiation triage systems are explored in-depth, along with a global survey of practices and protocols. Finally, this review also focuses on in vivo detection systems and their capacities for radionuclide identification, prioritizing internalized gamma-emitting isotopes due to their broader relevance. Collectively, this study comprehensively addresses the intricacies of triage management following radiation emergencies, emphasizing the imperative for enhanced standardization and continued research in this critical domain.

Comparative study on measurements of radiochromic films using portable colorimeters

The recently proposed method for on-site radiation dosimetry by a combination of radiochromic film and portable colorimeter was tested for six combinations of two popular Gafchromic films (EBT3 and EBT-XD) and three commercially available portable colorimeters (nix pro2, nix spectro2 and Spectro1 Pro; abbreviated to "NixP", "NixS" and "SpoP", respectively). EBT3 and EBT-XD were irradiated with X-rays (160 kV, 6.3 mA) up to 40 Gy and 80 Gy, respectively, and the radiation-induced color levels of RGB and CMYK components were measured with the three colorimeters. Angle dependence was examined by reading at 15° intervals. As a result, it was judged that all combinations would work effectively under certain irradiation conditions. NixP and NixS were applicable to a wider dose range for both films, while SpoP fit a lower dose range. On the other hand, SpoP showed an advantageous feature of no angular dependence in reading films, while NixP and NixS showed significant angle-dependent changes. These differences are considered to be attributable to the different geometries of LED light emission, which came from all directions (360°) in SpoP, 4 directions in NixP, and 8 directions in NixS. These findings are expected to expand the applicability of the novel method to various occasions of on-site dosimetry.

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.

Development of high-throughput systems for biodosimetry

Biomarkers for ionising radiation exposure have great utility in scenarios where there has been a potential exposure and physical dosimetry is missing or in dispute, such as for occupational and accidental exposures. Biomarkers that respond as a function of dose are particularly useful as biodosemeters to determine the dose of radiation to which an individual has been exposed. These dose measurements can also be used in medical scenarios to track doses from medical exposures and even have the potential to identify an individual's response to radiation exposure that could help tailor treatments. The measurement of biomarkers of exposure in medicine and for accidents, where a larger number of samples would be required, is limited by the throughput of analysis (i.e. the number of samples that could be processed and analysed), particularly for microscope-based methods, which tend to be labour-intensive. Rapid analysis in an emergency scenario, such as a large-scale accident, would provide dose estimates to medical practitioners, allowing timely administration of the appropriate medical countermeasures to help mitigate the effects of radiation exposure. In order to improve sample throughput for biomarker analysis, much effort has been devoted to automating the process from sample preparation through automated image analysis. This paper will focus mainly on biological endpoints traditionally analysed by microscopy, specifically dicentric chromosomes, micronuclei and gamma-H2AX. These endpoints provide examples where sample throughput has been improved through automated image acquisition, analysis of images acquired by microscopy, as well as methods that have been developed for analysis using imaging flow cytometry.

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.

EPR investigation of gamma-irradiated FAMOSER drug for DOSIMETRIC purposes

Exposure to ionizing radiation can also lead to the formation of stable or unstable radicals in the structures of drugs, as in many materials. The concentrations of these radicals may show a linear dependence on the radiation dose exposed. Since drugs are materials that can be found next to or on radiation victims during a possible nuclear or radiological accident, it is very meaningful to determine the Electron Paramagnetic Resonance (EPR) dosimetric properties of stable radicals in their structures. In this study, the dosimetric properties of Famoser, which is one of the stomach-relieving drugs that people often have with them in their daily life, in the dose range of 10-800 Gy were investigated by EPR technique.

DDB2 and MDM2 genes are promising markers for radiation diagnosis and estimation of radiation dose independent of trauma and burns

In the field of biodosimetry, the current accepted method for evaluating radiation dose fails to meet the need of rapid, large-scale screening, and most RNA marker-related studies of biodosimetry are concentrating on a single type of ray, while some other potential factors, such as trauma and burns, have not been covered. Microarray datasets that contain the data of human peripheral blood samples exposed to X-ray, neutron, and γ-ray radiation were obtained from the GEO database. Totally, 33 multi-type ray co-induced genes were obtained at first from the differentially expressed genes (DEGs) and key genes identified by weighted gene co-expression network analysis (WGCNA), and these genes were mainly enriched in DNA damage, cellular apoptosis, and p53 signaling pathway. Following transcriptome sequencing of blood samples from 11 healthy volunteers, 13 patients with severe burns, and 37 patients with severe trauma, 6635 trauma-related DEGs and 7703 burn-related DEGs were obtained. Through the exclusion method, a total of 12 radiation-specific genes independent of trauma and burns were identified. ROC curve analysis revealed that the DDB2 gene performed the best in diagnosis of all three types of ray radiation, while correlation analysis showed that the MDM2 gene was the best in assessment of radiation dose. The results of multiple-linear regression analysis indicated that such analysis could improve the accuracy in assessment of radiation dose. Moreover, the DDB2 and MDM2 genes remained effective in radiation diagnosis and assessment of radiation dose in an external dataset. In general, the study brings new insights into radiation biodosimetry.

Development of a human peripheral blood ex vivo model for rapid protein biomarker detection and applications to radiation biodosimetry

In the event of a widespread radiological incident, thousands of people may be exposed to a wide range of ionizing radiation. In this unfortunate scenario, there will be a need to quickly screen a large number of people to assess the amount of radiation exposure and triage for medical treatment. In our earlier work, we previously identified and validated a panel of radiosensitive protein biomarkers in blood leukocytes, using the humanized-mouse and non-human primate (NHP) models. The objective of this work was to develop a high-throughput imaging flow-cytometry (IFC) based assay for the rapid measurement of protein biomarker expression in human peripheral blood samples irradiated ex vivo. In this assay design, peripheral human blood samples from healthy adult donors were exposed to 0-5 Gy X-irradiation ex vivo and cultured for up to 2 days. Samples were stained with a cocktail of surface antigens (CD66b, CD20, and CD3), fixed and permeabilized, and intracellularly stained for BAX (Bcl-2-associated X) protein, used here as a representative biomarker. Samples were interrogated by IFC, and a uniform analysis template was created to measure biomarker expression in heterogeneous and specific leukocyte subtype populations at each time point. In this human blood ex vivo model, we show that within gated populations of leukocyte subtypes, B-cells are highly radiosensitive with the smallest surviving fraction, followed by T-cells and granulocytes. Dose-dependent biomarker responses were measured in the lymphocytes, B-, and T-cell populations, but not in the granulocytes, with dose-response curves showing increasing fold changes in BAX protein expression up to Day 2 in lymphocyte populations. We present here the successful use of this ex vivo model for the development of radiation dose-response curves of a candidate protein biomarker towards future applications of dose reconstruction and biodosimetry.

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.

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

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

Establishment of ex vivo calibration curve for X-ray induced "dicentric + ring" and micronuclei in human peripheral lymphocytes for biodosimetry during radiological emergencies, and validation with dose blinded samples

In the modern developing society, application of radiation has increased extensively. With significant improvement in the radiation protection practices, exposure to human could be minimized substantially, but cannot be avoided completely. Assessment of exposure is essential for regulatory decision and medical management as applicable. Until now, cytogenetic changes have served as surrogate marker of radiation exposure and have been extensively employed for biological dose estimation of various planned and unplanned exposures. Dicentric Chromosomal Aberration (DCA) is radiation specific and is considered as gold standard, micronucleus is not very specific to radiation and is considered as an alternative method for biodosimetry. In this study dose response curves were generated for X-ray induced "dicentric + ring" and micronuclei, in lymphocytes of three healthy volunteers [2 females (age 22, 23 years) and 1 male (24 year)]. The blood samples were irradiated with X-ray using LINAC (energy 6 MV, dose rate 6 Gy/min), in the dose range of 0-5Gy. Irradiated blood samples were cultured and processed to harvest metaphases, as per standard procedures recommended by International Atomic Energy Agency. Pooled data obtained from all the three volunteers, were in agreement with Poisson distribution for "dicentric + ring", however over dispersion was observed for micronuclei. Data ("dicentric + ring" and micronuclei) were fitted by linear quadratic model of the expression Y[bond, double bond]C + αD + βD² using Dose Estimate software, version 5.2. The data fit has resulted in linear coefficient α = 0.0006 (±0.0068) "dicentric + ring" cell^-1 Gy^-1 and quadratic coefficient β = 0.0619 (±0.0043) "dicentric + ring" cell^-1 Gy^-2 for "dicentric + ring" and linear coefficient α = 0.0459 ± (0.0038) micronuclei cell^-1 Gy^-1 and quadratic coefficient β = 0.0185 ± (0.0010) micronuclei cell^-1 Gy^-2 for micronuclei, respectively. Background frequencies for "dicentric + ring" and micronuclei were 0.0006 ± 0.0004 and 0.0077 ± 0.0012 cell^-1, respectively. Established curves were validated, by reconstructing the doses of 8 dose blinded samples (4 by DCA and 4 by CBMN) using coefficients generated here. Estimated doses were within the variation of 0.9-16% for "dicentric + ring" and 21.7-31.2% for micronuclei respectively. These established curves have potential to be employed for biodosimetry of occupational, clinical and accidental exposures, for initial triage and medical management.

Candidate Gene Expression in Regional Population and Its Relevance for Radiation Triage

Quantification of gene expression signatures has been substantiated as a potential and rapid marker for radiation triage and biodosimetry during nuclear emergencies. Similar to the established biodosimetry assays, the gene expression assay has drawbacks such as being highly dynamic and transient, not specific to ionizing radiation, and also influenced by confounding factors such as gender, health status, lifestyle, and inflammation. In view of that, prior knowledge of baseline expression of certain candidate genes in a population could complement the discrimination of the unexposed from the exposed individuals without the need for individual pre-exposure controls. We intended to establish a baseline expression of reported radiation-responsive genes such as CDKN1A, DDB2, FDXR, and PCNA in the blood samples of healthy human participants and then compare it with diabetic/hypertension participants (as a chronic inflammatory condition) drawn from south Indian population. Further, we have examined the appropriateness of the assay for radiation triage-like situations; i.e., the expression profiles of those genes were examined in the participants who underwent X-ray-based medical imaging. Acute inflammation induced by lipopolysaccharide exposure in the blood significantly increased the fold expression of those genes (p < 0.0001) compared to the control. Whereas the basal expression level of those genes among the participants with the inflammatory condition is marginally higher than those observed in the healthy participants; despite the excess, the fold increase in those genes between the groups did not differ significantly. Consistent with the inflammatory participants, the basal expression level of those genes in the blood sample of participants who received X-radiation during neuro-interventional and computed tomography imaging is marginally higher than those observed in the pre-exposure of respective groups. Nevertheless, the fold increase in those genes did not differ significantly as the fold change fell within the two folds. Thus, overall results suggest that the utility of CDKN1A, DDB2, FDXR, and PCNA gene expression for radiation triage specific after very low-dose radiation exposure needs to be interpreted with caution for a much more reliable triage.

Methodology and Instrumentation for Electron Paramagnetic Resonance Dosimetry With Tooth Enamel

When tooth enamel is exposed to ionizing radiation, it generates a dose-dependent concentration of free radical centers (i.e., unpaired electrons). The concentration of these free radical centers is identified and quantified using electron paramagnetic resonance (EPR) spectroscopy in the form of an EPR spectrum. The intensity of the spectrum is proportional to the absorbed dose. Four international intercomparisons have already demonstrated that the EPR tooth enamel dosimetric technique is reliable for retrospective dose assessment in acute and chronic exposure scenarios. Additionally, EPR dosimetry is regarded same as a gold standard for reconstructing the total lifetime dose of individuals using tooth enamel. The accuracy and reproducibility of EPR dose reconstruction depend on the sample preparation, spectrum acquisition, and EPR spectra analysis techniques. So, this paper reviews some of the widely applied and accepted laboratory protocols or methodologies for the EPR dosimetric methods. The minimum detection limit in tooth enamel using this technique was 30 mGy. So, this review aims to share these protocols so that it would be easy to reconstruct the accident doses or chronic exposures with reliable accuracy and precision. Different bands (e.g., L, X, Q, etc.) continuous wave (CW) EPR spectrometers have been used in many historical and accident dose reconstructions; however, due to the availability, moderate price, and not being much influenced by the small amount of moisture in a sample, the X-band has been widely used. A well-developed methodology, a highly sensitive EPR spectrometer, and a well-trained operator are vital for the reliable measurements of absorbed low doses in EPR dosimetry with tooth enamel.

An estimate assay for low-level exposure to ionizing radiation based on mass spectrometry quantification of γ-H2AX in human peripheral blood lymphocytes

Exposure to environmental ionizing radiation (IR) is ubiquitous, and large-dose exposure to IR is known to cause DNA damage and genotoxicity which is associated with an increased risk of cancer. Whether such detrimental effects are caused by exposure to low-dose IR is still debated. Therefore, rapid and early estimation of absorbed doses of IR in individuals, especially at low levels, using radiation response markers is a pivotal step for early triage during radiological incidents to provide adequate and timely clinical interventions. However, there is currently a crucial shortage of methods capable of determining the extent of low-dose IR exposure to human beings. The phosphorylation of histone H2AX on serine 139 (designated γ-H2AX), a classic biological dosimeter, can be used to evaluate the DNA damage response. We have developed an estimation assay for low-level exposure to IR based on the mass spectrometry quantification of γ-H2AX in blood. Human peripheral blood lymphocytes sensitive to low-dose IR, maintaining low temperature (4°C) and adding enzyme inhibitor are proven to be key steps, possibly insuring that a stable and marked γ-H2AX signal in blood cells exposed to low-dose IR could be detected. For the first time, DNA damage at low dose exposures to IR as low as 0.01 Gy were observed using the sensitive variation of γ-H2AX with high throughput mass spectrometry quantification in human peripheral blood, which is more accurate than the previously reported methods by virtue of isotope-dilution mass spectrometry, and can observe the time effect of DNA damage. These in vitro cellular dynamic monitoring experiments show that DNA damage occurred rapidly and then was repaired slowly over the passage of post-irradiation time even after exposure to very low IR doses. This assay was also used to assess different radiation exposures at the in vitro cellular level. These results demonstrate the potential utility of this assay in radiation biodosimetry and environmental risk assessment.

Establishment of in vitro Calibration Curve for 60Co-γ-rays Induced Phospho-53BP1 Foci, Rapid Biodosimetry and Initial Triage, and Comparative Evaluations With γH2AX and Cytogenetic Assays

A rapid and reliable method for biodosimetry of populations exposed to ionizing radiation in the event of an incident or accident is crucial for initial triage and medical attention. DNA-double strand breaks (DSBs) are indicative of radiation exposure, and DSB-repair proteins (53BP1, γH2AX, ATM, etc.) are considered sensitive markers of DSB quantification. Phospho-53BP1 and γH2AX immunofluorescence technique serves as a sensitive, reliable, and reproducible tool for the detection and quantification of DSB-repair proteins, which can be used for biological dose estimations. In this study, dose-response curves were generated for ⁶⁰Co-γ-rays induced phospho-53 Binding Protein 1 (phospho-53BP1) foci at 1, 2, 4, 8, 16, and 24 h, post-irradiation for a dose range of 0.05–4 Gy using fluorescence microscopy. Following ISO recommendations, minimum detection limits (MDLs) were estimated to be 16, 18, 25, 40, 50, and 75 mGy for dose-response curves generated at 1, 2, 4, 8, 16, and 24 h post-irradiation. Colocalization and correlation of phospho-53BP1 and γH2AX were also measured in irradiated peripheral blood lymphocytes (PBLs) to gain dual confirmation. Comparative evaluation of the established curve was made by γH2AX-immunofluorescence, dicentric chromosome assay (DCA), and reciprocal translocation (RT) assays by reconstructing the dose of 6 dose-blinded samples. Coefficients of respective in-house established dose-response curves were employed to reconstruct the blind doses. Estimated doses were within the variation of 4.124%. For lower doses (0.052 Gy), phospho-53BP1 and γH2AX assays gave closer estimates with the variation of −4.1 to + 9% in comparison to cytogenetic assays, where variations were −8.5 to 24%. For higher doses (3 and 4 Gy), both the cytogenetic and immunofluorescence (phospho-53BP1 and γH2AX), assays gave comparable close estimates, with −11.3 to + 14.3% and −10.3 to −13.7%, variations, respectively.

Retrospective OSL Dosimetry With Common Pharmaceuticals and Food Supplements

Several common pharmaceuticals such as ibuprofen, paracetamol, aspirin, oral contraceptives, drugs for the prevention of motion sickness and food supplements such as table vitamins and minerals have been studied for the purposes of retrospective dosimetry using optically stimulated luminescence (OSL). The essence is that the tablets with these drug substances contain additive crystalline materials which, after irradiation and stimulation, may exhibit luminescence. For most of the pharmaceuticals and food supplements, a radiation-induced dose-dependent OSL signal was detected. Subsequently, basic dosimetric characteristics of the materials were studied, specifically sensitivity changes during repeated OSL readings, dose response, zero-dose, minimum detectable dose (MDD) and fading. The most radiation sensitive materials were food supplements with Mg providing zero-dose and MDD values at the level of several mGy. For Mg supplements, considerable sensitivity changes in OSL signal were observed. Despite this, they could be corrected using a Single-Aliquot Regenerative-dose (SAR) protocol. The OSL signals of the other materials were relatively weak but they were well reproducible and exhibited linear dose response. The MDD values were variable among the materials and ranged from 0.1 to several Gy. However, for some of the pharmaceuticals, a very high and variable zero-dose of more than 3 Gy was observed that would rule out the possibility of dose reconstruction for triage purposes. The OSL signal exhibited a significant fading rate for most of the materials. The measurements for dose reconstruction should be performed as soon as possible after irradiation, i.e. within a maximum of a few days.

Identification of novel biomarkers for acute radiation injury using multi-omics approach and nonhuman primate model

PURPOSE

The availability of validated biomarkers to assess radiation exposure and to assist in developing medical countermeasures remains an unmet need.

METHODS AND MATERIALS

We used a cobalt-60 gamma-irradiated nonhuman primate (NHP) model to delineate a multi-omics-based serum probability index of radiation exposure. Both male and female NHPs were irradiated with different doses ranging from 6.0 to 8.5 Gy, with 0.5 Gy increments between doses. We leveraged high-resolution mass spectrometry for analysis of metabolites, lipids, and proteins at 1, 2, and 6 days post-irradiation in NHP serum.

RESULTS

A logistic regression model was implemented to develop a 4-analyte panel to stratify irradiated NHPs from unirradiated with high accuracy that was agnostic for all doses of gamma-rays tested in the study, up to six days after exposure. This panel was comprised of Serpin Family A9, acetylcarnitine, PC (16:0/22:6), and suberylglycine, which showed 2 - 4-fold elevation in serum abundance upon irradiation in NHPs and can potentially be translated as a molecular diagnostic for human use following larger validation studies.

CONCLUSIONS

Taken together, this study, for the first time, demonstrates the utility of a combinatorial molecular characterization approach using an NHP model for developing minimally invasive assays from small volumes of blood that can be effectively used for radiation exposure assessments.

EPR dosimetry in glass: a review

Electron Paramagnetic Resonance (EPR) spectroscopy enables detection of paramagnetic centers generated in solids by ionising radiation. In the last years, the ubiquity of glass in personal utility items increased significance of fortuities retrospective dosimetry based on EPR in glass parts of mobile phones and watches. Despite of fading of the signals and their susceptibility to light, it enables dosimetry at medical triage level of 1-2 Gy. In this article information relevant for assessment of applicability and planning of the EPR dosimetry is presented-particularly at dose levels typical for radiation accidents. Reported data on fading of the radiation-induced spectral components are presented and compared. Effects of light on background spectra and on the dosimetric signals are also presented. It is concluded that when properly accounting for the fading and for the obscuring effects of light, the EPR dosimetry in glasses from mobile phones and watches can be used in dose assessment after radiation accidents.

A deep learning model (FociRad) for automated detection of γ-H2AX foci and radiation dose estimation

DNA double-strand breaks (DSBs) are the most lethal form of damage to cells from irradiation. γ-H2AX (phosphorylated form of H2AX histone variant) has become one of the most reliable and sensitive biomarkers of DNA DSBs. However, the γ-H2AX foci assay still has limitations in the time consumed for manual scoring and possible variability between scorers. This study proposed a novel automated foci scoring method using a deep convolutional neural network based on a You-Only-Look-Once (YOLO) algorithm to quantify γ-H2AX foci in peripheral blood samples. FociRad, a two-stage deep learning approach, consisted of mononuclear cell (MNC) and γ-H2AX foci detections. Whole blood samples were irradiated with X-rays from a 6 MV linear accelerator at 1, 2, 4 or 6 Gy. Images were captured using confocal microscopy. Then, dose-response calibration curves were established and implemented with unseen dataset. The results of the FociRad model were comparable with manual scoring. MNC detection yielded 96.6% accuracy, 96.7% sensitivity and 96.5% specificity. γ-H2AX foci detection showed very good F1 scores (> 0.9). Implementation of calibration curve in the range of 0-4 Gy gave mean absolute difference of estimated doses less than 1 Gy compared to actual doses. In addition, the evaluation times of FociRad were very short (< 0.5 min per 100 images), while the time for manual scoring increased with the number of foci. In conclusion, FociRad was the first automated foci scoring method to use a YOLO algorithm with high detection performance and fast evaluation time, which opens the door for large-scale applications in radiation triage.

The effectiveness of ornamental building materials (tiles) for retrospective thermoluminescence dosimetry

Like many other decorative building materials, tiles are one of the most precious ornamental ingredients for making a lucrative building image. It not only offers beauty and luxury but also added value by protecting/monitoring ionizing radiation. In this study, the utmost regular use of seven varieties of tile samples has been considered for retrospective thermoluminescence dosimetry. To observe the potentials of tiles for retrospective dosimetry, the major thermoluminescence properties (such as dose-response, energy dependence, self-sensitivity, relative sensitivity, glow curves, repeatability, fading, and also effective atomic number) has been investigated following the annealing - irradiation - readout cycles. Making an allowance for the various TL parameters, White Horse (Mirror Polish) tiles demonstrate suitability to be used as emergency TL dosimeter in 0.5-100 Gy dose array. Comparing the values of Z_eff of these numerous tiles' samples (11.6-12.7) with TLD-200 (Z_eff = 16.3), it is to be noted that tiles can be used as a suitable material for environmental radiation dosimetry. The thermoluminescent characteristics of tiles in the dose limit from 0.5 Gy to 100 Gy are reported here for the first time.

Peripheral Blood Transcript Signatures after Internal 131I-mIBG Therapy in Relapsed and Refractory Neuroblastoma Patients Identifies Early and Late Biomarkers of Internal 131I Exposures

131I-metaiodobenzylguanidine (131I-mIBG) is a targeted radiation therapy developed for the treatment of advanced neuroblastoma. We have previously shown that this patient cohort can be used to predict absorbed dose associated with early 131I exposure, 72 h after treatment. We now expand these studies to identify gene expression differences associated with 131I-mIBG exposure 15 days after treatment. Total RNA from peripheral blood lymphocytes was isolated from 288 whole blood samples representing 59 relapsed or refractory neuroblastoma patients before and after 131I-mIBG treatment. We found that several transcripts predictive of early exposure returned to baseline levels by day 15, however, selected transcripts did not return to baseline. At 72 h, all 17 selected pathway-specific transcripts were differentially expressed. Transcripts CDKN1A (P < 0.000001), FDXR (P < 0.000001), DDB2 (P < 0.000001), and BBC3 (P < 0.000001) showed the highest up-regulation at 72 h after 131I-mIBG exposure, with mean log2 fold changes of 2.55, 2.93, 1.86 and 1.85, respectively. At day 15 after 131I-mIBG, 11 of the 17 selected transcripts were differentially expressed, with XPC, STAT5B, PRKDC, MDM2, POLH, IGF1R, and SGK1 displaying significant up-regulation at 72 h and significant down-regulation at day 15. Interestingly, transcripts FDXR (P = 0.01), DDB2 (P = 0.03), BCL2 (P = 0.003), and SESN1 (P < 0.0003) maintained differential expression 15 days after 131I-mIBG treatment. These results suggest that transcript levels for DNA repair, apoptosis, and ionizing radiation-induced cellular stress are still changing by 15 days after 131I-mIBG treatment. Our studies showcase the use of biodosimetry gene expression panels as predictive biomarkers following early (72 h) and late (15 days) internal 131I exposure. Our findings also demonstrate the utility of our transcript panel to differentiate exposed from non-exposed individuals up to 15 days after exposure from internal 131I.

Dosimetry of heavy ion exposure to human cells using nanoscopic imaging of double strand break repair protein clusters

The human body is constantly exposed to ionizing radiation of different qualities. Especially the exposure to high-LET (linear energy transfer) particles increases due to new tumor therapy methods using e.g. carbon ions. Furthermore, upon radiation accidents, a mixture of radiation of different quality is adding up to human radiation exposure. Finally, long-term space missions such as the mission to mars pose great challenges to the dose assessment an astronaut was exposed to. Currently, DSB counting using γH2AX foci is used as an exact dosimetric measure for individuals. Due to the size of the γH2AX IRIF of ~ 0.6 µm, it is only possible to count DSB when they are separated by this distance. For high-LET particle exposure, the distance of the DSB is too small to be separated and the dose will be underestimated. In this study, we developed a method where it is possible to count DSB which are separated by a distance of ~ 140 nm. We counted the number of ionizing radiation-induced pDNA-PKcs (DNA-PKcs phosphorylated at T2609) foci (size = 140 nm ± 20 nm) in human HeLa cells using STED super-resolution microscopy that has an intrinsic resolution of 100 nm. Irradiation was performed at the ion microprobe SNAKE using high-LET 20 MeV lithium (LET = 116 keV/µm) and 27 MeV carbon ions (LET = 500 keV/µm). pDNA-PKcs foci label all DSB as proven by counterstaining with 53BP1 after low-LET γ-irradiation where separation of individual DSB is in most cases larger than the 53BP1 gross size of about 0.6 µm. Lithium ions produce (1.5 ± 0.1) IRIF/µm track length, for carbon ions (2.2 ± 0.2) IRIF/µm are counted. These values are enhanced by a factor of 2–3 compared to conventional foci counting of high-LET tracks. Comparison of the measurements to PARTRAC simulation data proof the consistency of results. We used these data to develop a measure for dosimetry of high-LET or mixed particle radiation exposure directly in the biological sample. We show that proper dosimetry for radiation up to a LET of 240 keV/µm is possible.

The Potential of Omics in Biological Dosimetry

Biological dosimetry is an internationally recognized method for quantifying and estimating radiation dose following suspected or verified excessive exposure to ionising radiation. In severe radiation accidents where a large number of people are potentially affected, it is possible to distinguish irradiated from non-irradiated people in order to initiate appropriate medical care if necessary. In addition to severe incidents caused by technical failure, environmental disasters, military actions, or criminal abuse, there are also radiation accidents in which only one or a few individuals are affected in the frame of occupational or medical exposure. The requirements for biological dosimetry are fundamentally different for these two scenarios. In particular, for large-scale radiation accidents, pre-screening methods are necessary to increase the throughput of samples for a rough first-dose categorization. The rapid development and increasing use of omics methods in research as well as in individual applications provides new opportunities for biological dosimetry. In addition to the discovery and search for new biomarkers, dosimetry assays based on omics technologies are becoming increasingly interesting and hold great potential, especially for large-scale dosimetry. In the following review, the different areas of biological dosimetry, the problems in finding suitable biomarkers, the current status of biomarker research based on omics, the potential applications of assays using omics technologies, and also the limitations for the different areas of biological dosimetry are discussed.

Reconstructive dosimetry and radiation dose evaluation of workers and public due to a Brazilian radiological accident in industrial radiography

Radiological accidents occur mainly in the practices recognized as high risk and which are classified by the International Atomic Energy Agency (IAEA) as Categories 1 and 2: radiotherapy, industrial irradiators and industrial radiography. In Brazil, five important cases in industrial gamma radiography occurred from 1985 to 2018, involving seven radiation workers and 19 members of the public. The accidents caused localized radiation lesions on the hands and fingers. One of these accidents is the focus of this paper. In this accident, a 3.28 TBq¹⁹²Ir radioactive source was left unshielded for 9 h in a non-destructive testing (NDT) company parking lot, and many radiation workers, employees and public, including teachers of a primary school were exposed. The radioactive source was also directly handled by a security worker for about 1.5 min causing severe radiation injuries in the hand and fingers. This paper presents radiation dose estimates for all accidentally exposed individuals. Four scenarios were considered, and three internationally recognised and updated reconstructive dosimetry techniques were used, named, Brazilian visual Monte Carlo Dose Calculation (VMC), virtual environment for radiological and nuclear accidents simulation (AVSAR) and RADPRO Calculator®. The main radiation doses estimated by VMC were the absorbed dose of 34 Gy for the security worker's finger and his effective dose of 91 mSv; effective doses from 43 to 160 mSv for radiation workers and NDT employees; and effective doses of 9 mSv for teachers in the schoolyard.

Clinical Applications of Biological Dosimetry in Patients Exposed to Low Dose Radiation Due to Radiological, Imaging or Nuclear Medicine Procedures

Radiation dosimetric biomarkers have found applications beyond radiation protection area and now are actively introduced into clinical practice. Cytogenetic assays appeared to be a valuable tool for individualized quantifying radiation effects in patients, with high capability for assessing genotoxicity of various medical exposure modalities and providing meaningful radiation dose estimates for prognoses of radiation-related cancer risk. This review summarized current data on the use of biological dosimetry methods in patients undergoing various medical irradiations to low doses. The highlighted topics include basic aspects of biological dosimetry and its limitations in the range of low radiation doses, and main patterns of in vivo induction of radiation biomarkers in clinical exposure scenarios, occurring in X-ray diagnostics, computed tomography, interventional radiology, low dose radiotherapy, and nuclear medicine (internally administered ¹³¹I and other radiopharmaceuticals). Additionally, several specific issues, examined by biodosimetry techniques, are analysed, such as contrast media effect, radiation response in pediatric patients, impact of magnetic resonance imaging, evaluation of radioprotectors, detection of patients' abnormal intrinsic radiosensitivity and dose estimation in persons involved in medical radiation incidents. A prognosis of possible directions for further improvements in this area includes the automation of cytogenetic analysis, introduction of molecular biodosimeters and development of multiparametric biodosimetry platforms. A potential approach to the advanced biodosimetry of internal exposure and/or low dose external irradiation is suggested; this can be a multiparametric platform based on the combination of the γ-H2AX foci, dicentric, and translocation assays, each applied in the optimum postexposure time range, with the amalgamation of the dose estimates. The study revealed the necessity of further research, which might clarify medical radiation safety concerns for patients via using stringent biodosimetry methodology.

Establishment and validation of surface model for biodosimetry based on γ-H2AX foci detection

INTRODUCTION

In the event of a radiation accident detecting γ-H2AX foci is being accepted as fast method for triage and dose assessment. However, due to their disappearance kinetics, published calibrations have been constructed at specific post-irradiation times.

OBJECTIVES

To develop a surface, or tridimensional, model to estimate doses at times not included in the calibration analysis, and to validate it.

MATERIALS AND METHODS

Calibration data was obtained irradiating peripheral mononucleated cells from one donor with radiation doses ranging from 0 to 3 Gy, and γ -H2AX foci were detected microscopically using a semi-automatic method, at different post-irradiation times from 0.5 to 24 h. For validation, in addition to the above-mentioned donor, blood samples from another donor were also used. Validation was done within the range of doses and post-irradiation times used in the calibration.

RESULTS

The calibration data clearly shows that at each analyzed time, the γ-H2AX foci frequency increases as dose increases, and for each dose this frequency decreases with post-irradiation time. The γ-H2AX foci nucleus distribution was clearly overdispersed, for this reason to obtain bidimensional and tridimensional dose-effect relationships no probability distribution was assumed, and linear and non-linear least squares weighted regression was used. In the two validation exercises for most evaluated samples, the 95% confidence limits of the estimated dose were between ±0.5 Gy of the real dose. No major differences were observed between donors.

CONCLUSION

In case of a suspected overexposure to radiation, the surface model here presented allows a correct dose estimation using γ-H2AX foci as biomarker. The advantage of this surface model is that it can be used at any post-irradiation time, in our model between 0.5 and 24 h.

Retrospective physical dosimetry in the Czech Republic: an overview of already established methods and recent research

PURPOSE

The threat of serious radiation exposures to members of the public from radiological incidents and nuclear events has led to intensive study of a number of emergency dosimetry techniques for purposes of triage. As such, a national laboratory of retrospective dosimetry was established in our institute. The purpose of this work is to provide a summary of the well-established and already implemented retrospective physical dosimetry techniques based on thermoluminescence (TL), optically stimulated luminescence (OSL) and neutron activation including their specifics. Moreover, we present some new results of the experimental work, in which we compared dosimetry potential of various dental repair materials and human teeth.

MATERIALS AND METHODS

At first, an overview of already established retrospective physical retrospective methods including their main features was compiled. As regards recent research, an experimental comparative study was performed under defined conditions. The materials used were aliquots prepared from both pure and repaired teeth and aliquots of unused dental ceramics of known type. Following irradiation, we compared TL and OSL curves of the materials. We also compared dosimetry characteristics of OSL signal as reproducibility, dose dependence and fading.

RESULTS

After irradiation, the teeth aliquots of dental enamel and dentin exhibited very low OSL and TL signals compared with aliquots containing some dental repair materials or aliquots of pure dental ceramics. With a few exceptions, the OSL signal of dental enamel and dentin aliquots irradiated to 2 Gy was hardly distinguishable from OSL signal corresponding to unirradiated aliquots. In contrast, aliquots of teeth containing some dental repair material and aliquots of pure dental ceramics provided a well reproducible OSL signal exhibiting linear dose response. All the materials tested exhibited a significant fading of the OSL signal. The loss of OSL signal during the first 24 hours after irradiation was from 20 to 99% of its original value obtained immediately after the irradiation.

CONCLUSIONS

The already established physical methods of retrospective dosimetry use a spectrum of verified materials and techniques for dose assessment in the aftermath of serious radiological incidents and nuclear events. In the comparative study, we found that the dosimetry potential of teeth in natural state is much worse compared to teeth repaired with dental ceramics or dental cement fillings. Teeth restored with dental repair materials exhibited relatively favorable dosimetry characteristics. However, they can be usable for a dose reconstruction only on condition that the main practical problems connected with fading and optical bleaching were solved.

X-band TE101 rectangular aperture cavity for in vivo EPR tooth dosimetry after radiation emergency

The TE101 mode rectangle EPR cavity was newly developed to achieve X-band in vivo EPR tooth dosimetry for the rescue of nuclear emergency. An aperture for sample detection was opened on the cavity's surface. Its characteristics were evaluated by measuring DPPH and intact human incisor samples. Remarkable radiation induced signal from EPR spectrum of 1Gy-8Gy irradiated teeth was observed. In vivo measurements of rat was performed to verify its application for in vivo tooth dosimetry.

Comparison of luminescence detectors of Al2O3:C, CaF2:Mn, LiF:Mg,Cu,P and quartz with respect to retrospective dose reconstructions using bricks

In the aftermath of an orphan radiation source find, a complex retrospective dose reconstruction can be required to estimate doses of persons who were staying in the vicinity. In retrospective dose reconstructions based on luminescence measurements of quartz extracted from bricks, high sensitivity thermoluminescence detectors (TLD) can be used as an ancillary tool for dose distribution measurements or natural radiation background measurement. We investigated the potential and limits of Al₂O₃:C, CaF₂:Mn and LiF:Mg,Cu,P detectors for such applications. We measured depth-dose profiles in bricks using quartz and the TLDs. We factored in important dosimetry characteristics such as dose response, energy response and detection threshold. The work included Monte Carlo simulations. Depth-dose profiles and radiation spectra inside of the bricks were calculated for purposes of comparison and interpretation. The measurements and calculations were performed for two different photon spectra with mean energies of 662 and 118 keV. As regards comparison of the measured and Monte Carlo calculated depth-dose profiles, the best agreement was found for LiF:Mg,Cu,P. Quartz, Al₂O₃:C and CaF₂:Mn tend to overestimate dose for lower photon energies and greater depths in bricks. The overestimation was the most marked for CaF₂:Mn. For measurements related to quartz, especially for natural radiation background dose measurement, the most suitable TLDs are Al₂O₃:C and LiF:Mg,Cu,P. CaF₂:Mn is the least useful material.

The potential of decorative building materials (marble) for retrospective thermoluminescence dosimetry

Among the various types of decorative materials used in Bangladeshi dwellings, the marble/marble stone is one of the most common ones that used largely for enhancing the beauty and/or aristocracy of the dwelling environment. In this study, the most commonly used, six types of marble stones, have been analyzed for retrospective accident dosimetry. With the interest of characterizing several key thermoluminescence properties to examine their potentiality for dosimetry, annealing - irradiation - readout steps have been done chronologically which comprises the analysis of glow curves, relative sensitivity, dose dependence, repeatability and fading. Considering the various TL parameters, marble 'Carrara' imported from Italy present relatively better capability for reconstruction of radiation dose in the dose range of 10-50 Gy. From fading result, it is clear that for reconstruction of absorbed dose up to four weeks of post exposure, the marble 'Carrara' is found to be the most reliable media among the studied marble types. The Z_eff values for the various marble samples are found to be in the range of 13.65-19.12, comparing favorably in replace of TLD-200 (Z_eff = 16.3) which can be used for low-level environmental radiation dosimetry. Present work constitutes the first study to investigate the potentials of marble stone for reconstruction of absorbed dose in the range of 10-50 Gy dose.

Radiation-Induced Immunity and Toxicities: The Versatility of the cGAS-STING Pathway

In the past decade, radiation therapy (RT) entered the era of personalized medicine, following the striking improvements in radiation delivery and treatment planning optimization, and in the understanding of the cancer response, including the immunological response. The next challenge is to identify the optimal radiation regimen(s) to induce a clinically relevant anti-tumor immunity response. Organs at risks and the tumor microenvironment (e.g. endothelial cells, macrophages and fibroblasts) often limit the radiation regimen effects due to adverse toxicities. Here, we reviewed how RT can modulate the immune response involved in the tumor control and side effects associated with inflammatory processes. Moreover, we discussed the versatile roles of tumor microenvironment components during RT, how the innate immune sensing of RT-induced genotoxicity, through the cGAS-STING pathway, might link the anti-tumor immune response, radiation-induced necrosis and radiation-induced fibrosis, and how a better understanding of the switch between favorable and deleterious events might help to define innovative approaches to increase RT benefits in patients with cancer.

The 2019-2020 EURADOS WG10 and RENEB Field Test of Retrospective Dosimetry Methods in a Small-Scale Incident Involving Ionizing Radiation

With the use of ionizing radiation comes the risk of accidents and malevolent misuse. When unplanned exposures occur, there are several methods which can be used to retrospectively reconstruct individual radiation exposures; biological methods include analysis of aberrations and damage of chromosomes and DNA, while physical methods rely on luminescence (TL/OSL) or EPR signals. To ensure the quality and dependability of these methods, they should be evaluated under realistic exposure conditions. In 2019, EURADOS Working Group 10 and RENEB organized a field test with the purpose of evaluating retrospective dosimetry methods as carried out in potential real-life exposure scenarios. A 1.36 TBq 192Ir source was used to irradiate anthropomorphic phantoms in different geometries at doses of several Gy in an outdoor open-air geometry. Materials intended for accident dosimetry (including mobile phones and blood) were placed on the phantoms together with reference dosimeters (LiF, NaCl, glass). The objective was to estimate radiation exposures received by individuals as measured using blood and fortuitous materials, and to evaluate these methods by comparing the estimated doses to reference measurements and Monte Carlo simulations. Herein we describe the overall planning, goals, execution and preliminary outcomes of the 2019 field test. Such field tests are essential for the development of new and existing methods. The outputs from this field test include useful experience in terms of planning and execution of future exercises, with respect to time management, radiation protection, and reference dosimetry to be considered to obtain relevant data for analysis.

Salty Crackers as Fortuitous Dosimeters: A Novel PSL Method for Rapid Radiation Triage

When a radiological and nuclear (R/N) emergency occurs, the categorization of individuals into those who are unaffected and those requiring medical intervention is a high priority. At times, a professional dosimeter is not available and therefore some common belongings may be used as fortuitous dosimeters. The preparation of these objects for the measurement should be such as to give the most accurate and precise results. This paper focused on the Photo-Stimulated Luminescence (PSL) response of salty crackers confronts the problem of sample preparation (mass, grain size), dose response and signal stability. The dose response was determined for doses up to 5 Gy, which allowed the calculation of the limit of detection. Additionally, the signal stability was investigated for samples irradiated with 0.3 and 3 Gy. The observed decrease of the signal does not prevent the detection in the dose range typical for R/N emergency. The main dosimetric characteristics were investigated by using two different models of PSL readers equipped with single (infrared) or double (infrared, blue light) stimulation. The results indicated that the limit of detection can be improved by applying blue light stimulation. Moreover, strong correlation of the measurements performed in the two different instruments, as well as the rapidity of the analysis and the simplicity of the operations, suggest that this method can be suitable for a rapid radiation triage of a large number of civilians in a mass casualty event. The study was simultaneously conducted by two laboratories (Ruder Bošković Institute, RBI, Croatia and Istituto Superiore di Sanità, ISS, Italy) involved in the BioPhyMeTRE project (grant No. G5684) supported by NATO Science for Peace and Security Programme.

Establishment and multiparametric-cytogenetic validation of 60Co-gamma-ray induced, phospho-gamma-H2AX calibration curve for rapid biodosimetry and triage management during radiological emergencies

Exposure to ionizing radiation is unavoidable to our modern developing society as its applications are widespread and increasing with societal development. The exposures may be planned as in medical applications or may be unplanned as in occupational work and radiological emergencies. Dose quantification of planned and unplanned exposures is essential to make crucial decisions for management of such exposures. This study aims to establish ex-vivo dose-response curve for ⁶⁰Co-gamma-ray induced gamma-H2AX-foci by immunofluorescence using microscopy and flowcytometry with human lymphocytes. This technique has the potential to serve as a rapid tool for dose estimation and triage application during small to large scale radiological emergencies and clinical exposures. Response curves were generated for the dose range 0-4 Gy (at 1, 2, 4, 8, 16, 24, 48, 72 and 96 h of incubation after irradiation) with microscopy and 0-8 Gy (at 2, 4, 8, 16 and 24 h of incubation after irradiation) with flow cytometry. These curves can be applied for dose reconstruction when post exposure sampling is delayed up to 96 h. In order to evaluate Minimum Detection Limit (MDL) of the assay, variation of background frequency of gamma-H2AX-foci was measured in 12 volunteers. To understand the application window of the assay, gamma-H2AX foci decay kinetics has been studied up to 96 h with microscopy and response curves were generated from 1 to 96 hours post exposure. Gamma-H2AX fluorescence intensity decay kinetics was also studied up to 96 h with flow cytometry and response curves were generated from 2 to 24 hours post irradiation. Established curves were validated with dose blinded samples and also compared with standard cytogenetic assays. An inter-comparison of dose estimates was made among gamma-H2AX assay, dicentric aberrations and reciprocal translocations for application window in various dose ranges and time of blood collection after exposures.

Use of Biological Dosimetry for Monitoring Medical Workers Occupationally Exposed to Ionizing Radiation

Medical workers are the largest group exposed to man-made sources of ionizing radiation. The annual doses received by medical workers have decreased over the last several decades, however for some applications, like fluoroscopically guided procedures, the occupational doses still remain relatively high. Studies show that for some procedures the operator and staff still use insufficient protective and dosimetric equipment, which might cause an underestimation of medical exposures. Physical dosimetry methods are a staple for estimating occupational exposures, although due to the inconsistent use of protection measures, an alternative method such as biological dosimetry might complement the physical methods to achieve a more complete picture. Such methods were used to detect exposures to doses as low as 0.1 mSv/year, and could be useful for a more accurate assessment of genotoxic effects of ionizing radiation in medical workers. Biological dosimetry is usually based on the measurement of the effects present in peripheral blood lymphocytes. Although some methods, such as chromosome aberration scoring or micronucleus assay, show promising results, currently there is no one method recognized as most suitable for dosimetric application in the case of chronic, low-dose exposures. In this review we decided to evaluate different methods used for biological dosimetry in assessment of occupational exposures of medical workers.

The design of X-band EPR cavity with narrow detection aperture for in vivo fingernail dosimetry after accidental exposure to ionizing radiation

For the purpose of assessing the radiation dose of the victims involved in the nuclear emergency or radiation accident, a new type of X-band EPR resonant cavity for in vivo fingernail EPR dosimetry was designed and a homemade EPR spectrometer for in vivo fingernail detection was constructed. The microwave resonant mode of the cavity was rectangular TE101, and there was a narrow aperture for fingernail detection opened on the cavity’s wall at the position of high detection sensitivity. The DPPH dot sample and the fingernail samples were measured based on the in vivo fingernail EPR spectrometer. The measurements of the DPPH dot sample verified the preliminary functional applicable of the EPR spectrometer and illustrated the microwave power and modulation response features. The fingernails after irradiation by gamma-ray were measured and the radiation-induced signal was acquired. The results indicated that the cavity and the in vivo EPR dosimeter instrument was able to detect the radiation-induced signal in irradiated fingernail, and preliminarily verified the basic function of the instrument and its potential for emergency dose estimate after a radiation accident.