UNCERTAINTY ON RADIATION DOSES ESTIMATED BY BIOLOGICAL AND RETROSPECTIVE PHYSICAL METHODS

Novel photopeak-independent correction method for internal activity calculation of 99mTc: a simulation study

This paper presents a new method for correcting the contribution of scattered radiation to the measurement of 99mTc internal activity in nuclear medicine patients using gamma cameras. So, this study aims to derive scattering correction factors by Monte Carlo simulation for anterior and posterior count rates (${I}_{\mathrm{A}}$ and ${I}_{\mathrm{P}}$) in the conjugate view method, enabling more precise estimation of activity A(t) compared to traditional trapezoidal and triangular approximations. The new approach eliminates the need to use photopeak for determining the fraction of scattered photons. Our results showed differences of <3% with respect to the real activity and 11% for the trapezoidal and triangular approaches.

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.

Beta irradiation-induced thermoluminescence: Glow curve analysis and kinetic parameters in combustion-synthesized undoped Ca4YO(BO3)3

This study examines the thermoluminescent (TL) properties of undoped Ca4YO(BO3)3 phosphor, focusing on how it behaves under a variety of experimental conditions. The IRSL-TL 565 nm was chosen as the appropriate detection filter among various optical detection filter combinations. During the preheating trials conducted at a rate of 2 °C/s, the TL peak exhibited increased intensity, particularly around 200 °C. The experimental outcomes demonstrated a reliable linear relationship (R2 = 0.996 and b = 1.015) in the dose response of undoped preheated Ca4YO(BO3)3 within the range of 1-200 Gy. The investigation encompasses a range of techniques, including the TM-Tstop method, computerized glow curve deconvolution (CGCD) analysis, and theoretical modelling. The application of the TM-Tstop method to samples irradiated with a 5 Gy dose revealed distinct zones on the TM versus Tstop diagram, signifying the presence of at least two discernible components within the TL glow curve, specifically, a single general order kinetics peak and a continuous distribution. The analysis of activation energy versus preheated temperature exhibited a stepwise curve, indicating five trap levels with depths ranging between 1.13 eV and 1.40 eV. The CGCD method also revealed the superposition of at least five distinct TL glow peaks. It was observed that their activation energies were consistent with the Tm-Tstop experiment. Furthermore, the low Figure of Merit (FOM) value of 1.18% indicates high reliability in the goodness-of-fit measure. These findings affirm the reliability and effectiveness of the employed methods in characterizing the TL properties of the Ca4YO(BO3)3 phosphor under investigation. Theoretical models, including the semi-localized transition model, were introduced to explain anomalous observations in TL glow peak intensities and heating rate patterns. While providing a conceptual framework, these models may require adjustments to accurately capture the specific characteristics uncovered through CGCD analysis. As a potential application, the study suggests that the characterized TL properties of Ca4YO(BO3)3 phosphor could be utilized in dosimetric applications, such as radiation dose measurements, owing to its reliable linear response within a broad dose range.

Comparing the effect of electron beam, beta and ultraviolet C exposure on the luminescence emission of commercial dosimeters

This paper reports on the luminescence characterization of TLD-100 (LiF: Ti, Mg), TLD-200 (CaF₂: Dy), TLD-400 (CaF₂: Mn) and GR-200 (LiF: Mg, Cu, P) dosimeters exposed to electro beam, beta and ultraviolet C radiation -UVC-. All of them show high sensitivity to radiation regardless of whether it is ionizing or partially ionizing radiation based on their luminescence properties (cathodoluminescence -CL- or thermoluminescence -TL-). CL emission differs significantly among them in shape and intensity due to their chemical compositions. LiF samples display three maxima at: (i) 300-450 nm linked to intrinsic and structural defects, (ii) a green waveband probably due to F₃⁺ centres or the presence of hydroxyl groups and (iii) the red-infrared emission band associated with F₂ centres. However, CL spectra from the CaF₂ dosimeters display meaningful differences due to the dopant. TLD-200 is characterized by an emission with four sharp individual peaks in the green-IR spectral region (due to the Dy³⁺), whilst TLD-400 exhibits a broad maximum peaked at ̴500 nm (linked to the Mn²⁺). On the other hand, the variation in the TL glow curves allows to discriminate the TLDs exposed to beta and UVC radiation since they give rise to different chemical-physical processes and that have been studied from the estimation of the kinetic parameters by means of the Computerised Glow Curve Deconvolution (CGCD) method.

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.

EURADOS STRATEGIC RESEARCH AGENDA 2020: VISION FOR THE DOSIMETRY OF IONISING RADIATION

Since 2012, the European Radiation Dosimetry Group (EURADOS) has developed its Strategic Research Agenda (SRA), which contributes to the identification of future research needs in radiation dosimetry in Europe. Continued scientific developments in this field necessitate regular updates and, consequently, this paper summarises the latest revision of the SRA, with input regarding the state of the art and vision for the future contributed by EURADOS Working Groups and through a stakeholder workshop. Five visions define key issues in dosimetry research that are considered important over at least the next decade. They include scientific objectives and developments in (i) updated fundamental dose concepts and quantities, (ii) improved radiation risk estimates deduced from epidemiological cohorts, (iii) efficient dose assessment for radiological emergencies, (iv) integrated personalised dosimetry in medical applications and (v) improved radiation protection of workers and the public. This SRA will be used as a guideline for future activities of EURADOS Working Groups but can also be used as guidance for research in radiation dosimetry by the wider community. It will also be used as input for a general European research roadmap for radiation protection, following similar previous contributions to the European Joint Programme for the Integration of Radiation Protection Research, under the Horizon 2020 programme (CONCERT). The full version of the SRA is available as a EURADOS report (www.eurados.org).

The effect of data aggregation on dispersion estimates in count data models

For the modelling of count data, aggregation of the raw data over certain subgroups or predictor configurations is common practice. This is, for instance, the case for count data biomarkers of radiation exposure. Under the Poisson law, count data can be aggregated without loss of information on the Poisson parameter, which remains true if the Poisson assumption is relaxed towards quasi-Poisson. However, in biodosimetry in particular, but also beyond, the question of how the dispersion estimates for quasi-Poisson models behave under data aggregation have received little attention. Indeed, for real data sets featuring unexplained heterogeneities, dispersion estimates can increase strongly after aggregation, an effect which we will demonstrate and quantify explicitly for some scenarios. The increase in dispersion estimates implies an inflation of the parameter standard errors, which, however, by comparison with random effect models, can be shown to serve a corrective purpose. The phenomena are illustrated by γ-H2AX foci data as used for instance in radiation biodosimetry for the calibration of dose-response curves.

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.

Evaluation of time-dependent strengths of californium neutron sources by decay of 252Cf, 250Cf, and 248Cm: Uncertainties by Monte Carlo method

A method for estimating source strength measurements of californium neutron sources is presented, based on the model of ²⁵²Cf, ²⁵⁰Cf, and ²⁴⁸Cm decay. This is combined with the Monte Carlo method (MCM) of propagating uncertainties. Californium sources were categorized into two types: Sort-A are those with most input quantities known while Sort-B are sources with only the mass at a certain reference date known. For Sort-A, the spread of all input quantities was estimated with Gaussian distribution and the deterministic 1st order GUM uncertainty propagation is applied to validate the MCM results. While, for Sort-B with inputs that have non-Gaussian distributions, only MCM is applied to evaluate uncertainties. Results show that for californium sources that are 25 y or older, a simple ²⁵²Cf decay correction is imprecise due to the contribution of ²⁵⁰Cf and ²⁴⁸Cm. The MCM was also shown to be a robust technique for uncertainty analysis that provides results for both Gaussian and non-Gaussian distributions. Moreover, the time-dependence of the contributors in the source strength and the corresponding uncertainties are presented. When exceedingly low uncertainties are not required, the calculation techniques presented in this work may serve as an alternative to actual measurements, which tend to be expensive.

Improving the accuracy of dose estimates from automatically scored dicentric chromosomes by accounting for chromosome number

PURPOSE

The traditional workflow for biological dosimetry based on manual scoring of dicentric chromosomes is very time consuming. Especially for large-scale scenarios or for low-dose exposures, high cell numbers have to be analyzed, requiring alternative scoring strategies. Semi-automatic scoring of dicentric chromosomes provides an opportunity to speed up the standard workflow of biological dosimetry. Due to automatic metaphase and chromosome detection, the number of counted chromosomes per metaphase is variable. This can potentially introduce overdispersion and statistical methods for conventional, manual scoring might not be applicable to data obtained by automatic scoring of dicentric chromosomes, potentially resulting in biased dose estimates and underestimated uncertainties. The identification of sources for overdispersion enables the development of methods appropriately accounting for increased dispersion levels.

MATERIALS AND METHODS

Calibration curves based on in vitro irradiated (137-Cs; 0.44 Gy/min) blood from three healthy donors were analyzed for systematic overdispersion, especially at higher doses (>2 Gy) of low LET radiation. For each donor, 12 doses in the range of 0-6 Gy were scored semi-automatically. The effect of chromosome number as a potential cause for the observed overdispersion was assessed. Statistical methods based on interaction models accounting for the number of detected chromosomes were developed for the estimation of calibration curves, dose and corresponding uncertainties. The dose estimation was performed based on a Bayesian Markov-Chain-Monte-Carlo method, providing high flexibility regarding the implementation of priors, likelihood and the functional form of the association between predictors and dicentric counts. The proposed methods were validated by simulations based on cross-validation.

RESULTS

Increasing dose dependent overdispersion was observed for all three donors as well as considerable differences in dicentric counts between donors. Variations in the number of detected chromosomes between metaphases were identified as a major source for the observed overdispersion and the differences between donors. Persisting overdispersion beyond the contribution of chromosome number was modeled by a Negative Binomial distribution. Results from cross-validation suggested that the proposed statistical methods for dose estimation reduced bias in dose estimates, variability between dose estimates and improved the coverage of the estimated confidence intervals. However, the 95% confidence intervals were still slightly too permissive, suggesting additional unknown sources of apparent overdispersion.

CONCLUSIONS

A major source for the observed overdispersion could be identified, and statistical methods accounting for overdispersion introduced by variations in the number of detected chromosomes were developed, enabling more robust dose estimation and quantification of uncertainties for semi-automatic counting of dicentric chromosomes.

Eurados review of retrospective dosimetry techniques for internal exposures to ionising radiation and their applications

This work presents an overview of the applications of retrospective dosimetry techniques in case of incorporation of radionuclides. The fact that internal exposures are characterized by a spatially inhomogeneous irradiation of the body, which is potentially prolonged over large periods and variable over time, is particularly problematic for biological and electron paramagnetic resonance (EPR) dosimetry methods when compared with external exposures. The paper gives initially specific information about internal dosimetry methods, the most common cytogenetic techniques used in biological dosimetry and EPR dosimetry applied to tooth enamel. Based on real-case scenarios, dose estimates obtained from bioassay data as well as with biological and/or EPR dosimetry are compared and critically discussed. In most of the scenarios presented, concomitant external exposures were responsible for the greater portion of the received dose. As no assay is available which can discriminate between radiation of different types and different LETs on the basis of the type of damage induced, it is not possible to infer from these studies specific conclusions valid for incorporated radionuclides alone. The biological dosimetry assays and EPR techniques proved to be most applicable in cases when the radionuclides are almost homogeneously distributed in the body. No compelling evidence was obtained in other cases of extremely inhomogeneous distribution. Retrospective dosimetry needs to be optimized and further developed in order to be able to deal with real exposure cases, where a mixture of both external and internal exposures will be encountered most of the times.

Use of molecularly-cloned haematopoietic growth factors in persons exposed to acute high-dose, high-dose rate whole-body ionizing radiations

Exposure to acute, high-dose, high dose-rate whole-body ionizing radiations damages the bone marrow resulting in rapid decreases in concentrations of blood cells, especially lymphocytes, granulocytes and platelets with associated risks of infection and bleeding. In several experimental models including non-human primate radiation exposure models giving molecularly cloned haematopoietic growth factor including granulocyte/macrophage colony-stimulating factor (G/M-CSF; sargramostim) and granulocyte colony-stimulating factor (G-CSF; filgrastim and pegylated G-CSF [peg-filgrastim]) accelerates bone marrow recovery and increases survival. Based on these data these molecules are US FDA approved for treating victims of radiation and nuclear incidents, accident and events such as nuclear terrorism and are included in the US National Strategic Stockpile. We discuss the immediate medical response to these events including how to estimate radiation dose and uniformity and which interventions are appropriate in different radiation exposures settings. We also discuss similarities and differences between molecularly cloned haematopoietic growth factors.

CONCEPTS OF OPERATIONS FOR A US DOSIMETRY AND BIODOSIMETRY NETWORK

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

Emergency response to radiological and nuclear accidents and incidents

Bone marrow damage is an important consequence of exposure to acute high-dose whole-body radiation. As such, haematologists can play an important role in managing this complication. However, these accident and incident scenarios are complex and often involve injuries to other organs and tissues from heat, projectiles and chemicals. In the case of a large-scale event there will likely be severe infrastructure disruptions and injury or death to medical personnel. Accurate estimates of dose and uniformity of exposure are needed to intelligently direct appropriate interventions, which range from antibiotics, antifungals and anti-virus drugs, molecularly-cloned haematopoietic growth factors and, in rare instances, haematopoietic cell transplants. These therapies are ones that haematologists often use in the context of anti-cancer therapy, especially therapy of haematological cancers like leukaemia. However, most haematologists have little knowledge of radiation biology and should consider updating this aspect of their expertise in continuing medical education. As in other areas of medicine, prevention is better than cure and haematologists should be active in decreasing risks of a nuclear war.

BIODOSIMETRY AND BIODOSIMETRY NETWORKS FOR MANAGING RADIATION EMERGENCY

Biological dosimetry enables individual dose reconstruction in the case of unclear or inconsistent radiation exposure situations, especially when a direct measurement of ionizing radiation is not or is no longer possible. To be prepared for large-scale radiological incidents, networking between well-trained laboratories has been identified as a useful approach for provision of the fast and trustworthy dose assessments needed in such circumstances. To this end, various biodosimetry laboratories worldwide have joined forces and set up regional and/or nationwide networks either on a formal or informal basis. Many of these laboratories are also a part of global networks such as those organized by World Health Organization, International Atomic Energy Agency or Global Health Security Initiative. In the present report, biodosimetry networks from different parts of the world are presented, and the partners, activities and cooperation actions are detailed. Moreover, guidance for situational application of tools used for individual dosimetry is given.

Optically stimulated luminescence (OSL) dosimetry in irradiated alumina substrates from mobile phone resistors

In this study the dosimetric properties of alumina (Al₂O₃) substrates found in resistors retrieved from mobile phones were investigated. Measurements of the decline of optically stimulated luminescence (OSL) generated following exposure of these substrates to ionising radiation showed that 16% of the signal could still be detected after 2 years (735 days). Further, the magnitude of the regenerative dose (calibration dose; D _i) had no impact on the accuracy of dose estimates. Therefore, it is recommended that the D _i be set as low as is practicable, so as to accelerate data retrieval. The critical dose, D _CL, and dose limit of detection, D _DL, taking into account the uncertainty in the dose-response relation as well as the uncertainty in the background signal, was estimated to be 7 and 13 mGy, respectively, 1 h after exposure. It is concluded that given the significant long-term component of fading, an absorbed dose of 0.5 Gy might still be detectable up to 6 years after the exposure. Thus, OSL from alumina substrates can be used for dosimetry for time periods far in excess of those previously thought.