Radiation dose rate effects: what is new and what is needed?

Despite decades of research to understand the biological effects of ionising radiation, there is still much uncertainty over the role of dose rate. Motivated by a virtual workshop on the "Effects of spatial and temporal variation in dose delivery" organised in November 2020 by the Multidisciplinary Low Dose Initiative (MELODI), here, we review studies to date exploring dose rate effects, highlighting significant findings, recent advances and to provide perspective and recommendations for requirements and direction of future work. A comprehensive range of studies is considered, including molecular, cellular, animal, and human studies, with a focus on low linear-energy-transfer radiation exposure. Limits and advantages of each type of study are discussed, and a focus is made on future research needs.

Cognitive effects of low dose of ionizing radiation - Lessons learned and research gaps from epidemiological and biological studies.

The last decades have seen increased concern about the possible effects of low to moderate doses of ionizing radiation (IR) exposure on cognitive function. An interdisciplinary group of experts (biologists, epidemiologists, dosimetrists and clinicians) in this field gathered together in the framework of the European MELODI workshop on non-cancer effects of IR to summarise the state of knowledge on the topic and elaborate research recommendations for future studies in this area. Overall, there is evidence of cognitive effects from low IR doses both from biology and epidemiology, though a better characterization of effects and understanding of mechanisms is needed. There is a need to better describe the specific cognitive function or diseases that may be affected by radiation exposure. Such cognitive deficit characterization should consider the human life span, as effects might differ with age at exposure and at outcome assessment. Measurements of biomarkers, including imaging, will likely help our understanding on the mechanism of cognitive-related radiation induced deficit. The identification of loci of individual genetic susceptibility and the study of gene expression may help identify individuals at higher risk. The mechanisms behind the radiation induced cognitive effects are not clear and are likely to involve several biological pathways and different cell types. Well conducted research in large epidemiological cohorts and experimental studies in appropriate animal models are needed to improve the understanding of radiation-induced cognitive effects. Results may then be translated into recommendations for clinical radiation oncology and imaging decision making processes.

Catalytic wet air oxidation of high BPA concentration over iron-based catalyst supported on orthophosphate.

The catalytic performance of Fe supported on nickel phosphate (NiP) was evaluated for the removal of bisphenol A (BPA) by catalytic wet air oxidation (CWAO) at 140 °C and 25 bar of pure oxygen pressure. The prepared NiP and Fe/NiP materials were fully characterized by XRD, N2-physisorption, H2-TPR, TEM, and ICP analysis. Iron (Fe/NiP) impregnation of NiP support enhanced the BPA removal efficiency from 37.0 to 99.6% when CWAO was performed. This catalyst was highly stable given the operating conditions of acidic medium, high temperature, and high pressure. The Fe/NiP catalyst showed an outstanding catalytic activity for oxidation of BPA, achieving almost complete removal of BPA in 180 min at a concentration of 300 mg/L, using 4 g/L of Fe/NiP. No iron leaching was detected after the CWAO of BPA. The stability of Fe/NiP was performed over three consecutive cycles, noting that BPA conversion was not affected and iron leaching was negligible. Therefore, this catalyst (Fe/NiP) could be considered as an innocuous and effective long-lasting catalyst for the oxidation of harmful organic molecules.

Cytogenetic damage analysis in mice chronically exposed to low-dose internal tritium beta-particle radiation.

The aim of this study was to carry out a comprehensive examination of potential genotoxic effects of low doses of tritium delivered chronically to mice and to compare these effects to the ones resulting from equivalent doses of gamma-irradiation. Mice were chronically exposed for one or eight months to either tritiated water (HTO) or organically bound tritium (OBT) in drinking water at concentrations of 10 kBq/L, 1 MBq/L or 20 MBq/L. Dose rates of internal ß-particle resulting from such tritium treatments were calculated and matching external gamma-exposures were carried out. We measured cytogenetic damage in bone marrow and in peripheral blood lymphocytes (PBLs) and the cumulative tritium doses (0.009 - 181 mGy) were used to evaluate the dose-response of OBT in PBLs, as well as its relative biological effectiveness (RBE). Neither tritium, nor gamma exposures produced genotoxic effects in bone marrow. However, significant increases in chromosome damage rates in PBLs were found as a result of chronic OBT exposures at 1 and 20 M Bq/L, but not at 10 kBq/L. When compared to an external acute gamma-exposure ex vivo, the RBE of OBT for chromosome aberrations induction was evaluated to be significantly higher than 1 at cumulative tritium doses below 10 mGy. Although found non-existent at 10 kBq/L (the WHO limit), the genotoxic potential of low doses of tritium (>10 kBq/L), mainly OBT, may be higher than currently assumed.

Twenty years of FISH-based translocation analysis for retrospective ionizing radiation biodosimetry.

PURPOSE: The fluorescent in situ hybridization (FISH) technique, which easily detects reciprocal translocations, is currently used to estimate doses in retrospective biological dosimetry, after suspected accidental overexposure to ionizing radiation (IR). This study of 42 cases aimed to verify the appropriateness of this assay for radiation dose reconstruction, compared to the dicentric assay, and to evaluate other limitations. MATERIAL AND METHODS: We labeled chromosomes 2, 4, and 12 by 3-color FISH painting to detect translocations on lymphocytes of patients with suspected past IR overexposure. RESULT: Translocation dose estimation showed doses significantly different from 0 Gy in 25 of the 42 cases. The lowest positive dose measured was 0.3 Gy. Several months after IR exposure, the doses measured by translocation and dicentric assays are quite similar. For a year, dose estimation by translocation assay becomes more relevant as dicentric frequency starts to decrease, coming close to 0 for more than a year after the exposure. The persistence of translocations enabled us to corroborate an overexposure 44 years earlier. Interpretation of the observed translocation yield requires the knowledge of the patient's other radiation exposures. A dose assessment by this biomarker is relevant only if the radiation exposure is confirmed. CONCLUSIONS: This technique is appropriate for corroborating a former IR exposure of individuals. When the radiation dose is greater than 1 Gy, the translocations in complex exchanges must be considered. Another relevant point is the use of an appropriate background yield of translocations. The dose assessment, however, also depends on exposure to various genotoxic agents besides IR. If no evidence about the existence of radiation exposure is available, dose assessment is not useful. For this reason, report only the translocation frequency and its comparison with the background yield by age class is preferable.

Uncertainty of fast biological radiation dose assessment for emergency response scenarios.

PURPOSE: Reliable dose estimation is an important factor in appropriate dosimetric triage categorization of exposed individuals to support radiation emergency response. MATERIALS AND METHODS: Following work done under the EU FP7 MULTIBIODOSE and RENEB projects, formal methods for defining uncertainties on biological dose estimates are compared using simulated and real data from recent exercises. RESULTS: The results demonstrate that a Bayesian method of uncertainty assessment is the most appropriate, even in the absence of detailed prior information. The relative accuracy and relevance of techniques for calculating uncertainty and combining assay results to produce single dose and uncertainty estimates is further discussed. CONCLUSIONS: Finally, it is demonstrated that whatever uncertainty estimation method is employed, ignoring the uncertainty on fast dose assessments can have an important impact on rapid biodosimetric categorization.

RENEB - Running the European Network of biological dosimetry and physical retrospective dosimetry.

PURPOSE: A European network was initiated in 2012 by 23 partners from 16 European countries with the aim to significantly increase individualized dose reconstruction in case of large-scale radiological emergency scenarios. RESULTS: The network was built on three complementary pillars: (1) an operational basis with seven biological and physical dosimetric assays in ready-to-use mode, (2) a basis for education, training and quality assurance, and (3) a basis for further network development regarding new techniques and members. Techniques for individual dose estimation based on biological samples and/or inert personalized devices as mobile phones or smart phones were optimized to support rapid categorization of many potential victims according to the received dose to the blood or personal devices. Communication and cross-border collaboration were also standardized. To assure long-term sustainability of the network, cooperation with national and international emergency preparedness organizations was initiated and links to radiation protection and research platforms have been developed. A legal framework, based on a Memorandum of Understanding, was established and signed by 27 organizations by the end of 2015. CONCLUSIONS: RENEB is a European Network of biological and physical-retrospective dosimetry, with the capacity and capability to perform large-scale rapid individualized dose estimation. Specialized to handle large numbers of samples, RENEB is able to contribute to radiological emergency preparedness and wider large-scale research projects.

Biomarkers for Uranium Risk Assessment for the Development of the CURE (Concerted Uranium Research in Europe) Molecular Epidemiological Protocol.

Despite substantial experimental and epidemiological research, there is limited knowledge of the uranium-induce health effects after chronic low-dose exposures in humans. Biological markers can objectively characterize pathological processes or environmental responses to uranium and confounding agents. The integration of such biological markers into a molecular epidemiological study would be a useful approach to improve and refine estimations of uranium-induced health risks. To initiate such a study, Concerted Uranium Research in Europe (CURE) was established, and involves biologists, epidemiologists and dosimetrists. The aims of the biological work package of CURE were: 1. To identify biomarkers and biological specimens relevant to uranium exposure; 2. To define standard operating procedures (SOPs); and 3. To set up a common protocol (logistic, questionnaire, ethical aspects) to perform a large-scale molecular epidemiologic study in uranium-exposed cohorts. An intensive literature review was performed and led to the identification of biomarkers related to: 1. retention organs (lungs, kidneys and bone); 2. other systems/organs with suspected effects (cardiovascular system, central nervous system and lympho-hematopoietic system); 3. target molecules (DNA damage, genomic instability); and 4. high-throughput methods for the identification of new biomarkers. To obtain high-quality biological materials, SOPs were established for the sampling and storage of different biospecimens. A questionnaire was developed to assess potential confounding factors. The proposed strategy can be adapted to other internal exposures and should improve the characterization of the biological and health effects that are relevant for risk assessment.

Concerted Uranium Research in Europe (CURE): toward a collaborative project integrating dosimetry, epidemiology and radiobiology to study the effects of occupational uranium exposure.

The potential health impacts of chronic exposures to uranium, as they occur in occupational settings, are not well characterized. Most epidemiological studies have been limited by small sample sizes, and a lack of harmonization of methods used to quantify radiation doses resulting from uranium exposure. Experimental studies have shown that uranium has biological effects, but their implications for human health are not clear. New studies that would combine the strengths of large, well-designed epidemiological datasets with those of state-of-the-art biological methods would help improve the characterization of the biological and health effects of occupational uranium exposure. The aim of the European Commission concerted action CURE (Concerted Uranium Research in Europe) was to develop protocols for such a future collaborative research project, in which dosimetry, epidemiology and biology would be integrated to better characterize the effects of occupational uranium exposure. These protocols were developed from existing European cohorts of workers exposed to uranium together with expertise in epidemiology, biology and dosimetry of CURE partner institutions. The preparatory work of CURE should allow a large scale collaborative project to be launched, in order to better characterize the effects of uranium exposure and more generally of alpha particles and low doses of ionizing radiation.

A mouse model of cytogenetic analysis to evaluate caesium137 radiation dose exposure and contamination level in lymphocytes.

In case of external overexposure to ionizing radiation, an estimation of its genotoxic effects on exposed individuals can be made retrospectively by the measurement of radiation-induced chromosome aberrations on circulating lymphocytes. Compared with external irradiation, intakes of radionuclides may, however, lead to specific features influencing dose distribution at the scale of body, of tissue or even of cell. Therefore, in case of internal contamination by radionuclides, experimental studies, particularly using animal models, are required to better understand mechanisms of their genotoxic effects and to better estimate the absorbed dose. The present study was designed to evaluate a cytogenetic method in mouse peripheral blood lymphocytes that would allow determination of yields and complexities of chromosome aberrations after low-dose rate exposure to (137)Cs delivered in vitro either by irradiation or by contamination. By using M-FISH analysis, we compared the low-dose rate responses observed in mouse to the high-dose rate responses observed both in mouse and in human. Promising similarities between the two species in the relative biological effect evaluation show that our cytogenetic model established in mouse might be useful to evaluate various radiation exposures, particularly relevant in case of intakes of radionuclides.

Lymphoepithelial Carcinoma of the Sublingual Gland: Case Report and Review of the Literature.

Lymphoepithelial carcinoma represents only 0.4% of salivary gland neoplasms. Generally affecting the parotid gland, it has been reported only twice in the sublingual gland. Controversies concerning the treatment of lymphoepithelial carcinoma exist. Although the literature generally agrees that primary surgery with adjuvant radiotherapy is part of the treatment, the benefit of adjuvant chemotherapy is not well described. This report describes the case of a 55-year-old man diagnosed with lymphoepithelial carcinoma of the sublingual gland. The patient was admitted for progressive pain in the floor of the mouth associated with trismus. Biopsy examination confirmed the diagnosis of lymphoepithelial carcinoma of the sublingual gland and magnetic resonance imaging showed multiple left lymphadenopathies. Surgery consisted of a radical neck dissection type III, surgical resection of the floor of the mouth, and reconstruction with a left facial artery musculomucosal flap. The patient received adjuvant radiotherapy (60 Gy) and adjuvant chemotherapy (3 cycles of cisplatinum 100 mg/m(2)). The patient was disease free at 36 months of follow-up. The evidence base for administering adjuvant chemotherapy in this situation is discussed.

Detection of partial-body exposure to ionizing radiation by the automatic detection of dicentrics.

In accidental exposure to ionizing radiation, it is essential to estimate the dose received by the victims. Currently dicentric scoring is the best biological indicator of exposure. The standard biological dosimetry procedure (500 metaphases scored manually) is suitable for a few dose estimations, but the time needed for analysis can be problematic in the case of a large-scale accident. Recently, a new methodology using automatic detection of dicentrics has greatly decreased the time needed for dose estimation and preserves the accuracy of the estimation. However, the capability to detect nonhomogeneous partial-body exposures is an important advantage of dicentric scoring-based biodosimetry, and this remains to be tested with automatic scoring. Thus we analyzed the results obtained with in vitro blood dilutions and in real cases of accidental exposure (partial- or whole-body exposure) using manual scoring and automatic detection of dicentrics. We confirmed that automatic detection allows threefold quicker dicentric scoring than the manual procedure with similar dose estimations and uncertainty intervals. The results concerning partial-body exposures were particularly promising, and homogeneously exposed samples were correctly distinguished from heterogeneously exposed samples containing 5% to 75% of blood irradiated with 2 Gy. In addition, the results obtained for real accident cases were similar whatever the methodology used. This study demonstrates that automatic detection of dicentrics is a credible alternative for recent and acute cases of whole- and partial-body accidental exposures to ionizing radiation.

Quantification of gamma-H2AX foci in human lymphocytes: a method for biological dosimetry after ionizing radiation exposure.

Recent studies have suggested that visualization of gamma-H2AX nuclear foci can be used to estimate exposure to very low doses of ionizing radiation. Although this approach is widely used for various purposes, its suitability for individual human biodosimetry has not yet been assessed. We therefore conducted such an assessment with the help of available software for observing and automatically scoring gamma-H2AX foci. The presence of gamma-H2AX foci was evaluated in human peripheral blood lymphocytes exposed ex vivo to gamma rays in a dose range of 0.02 to 2 Gy. We analyzed the response of gamma-H2AX to ionizing radiation in relation to dose, time after exposure, and individual variability. We constructed dose-effect calibration curves at 0.5, 8 and 16 h after exposure and evaluated the threshold of detection of the technique. The results show the promise of automatic gamma-H2AX scoring for a reliable assessment of radiation doses in a dose range of 0.6 Gy to 2 Gy up to 16 h after exposure. This gamma-H2AX-based assay may be useful for biodosimetry, especially for triage to distinguish promptly among individuals the ones who have received negligible doses from those with significantly exposures who are in need of immediate medical attention. However, additional in vivo experiments are needed for validation.

Induction of gamma-H2AX foci in human exfoliated buccal cells after in vitro exposure to ionising radiation.

PURPOSE: To test the gamma-H2AX (Histone 2AX phosphorylation of serine 139) foci assay for the detection of ionising radiation-induced DNA damage in buccal exfoliated cells. MATERIALS AND METHODS: Buccal mucosa cells from five individuals (three females, two males, aged 26-47 years) were exposed to 0, 0.5, 1, 2 and 4 Gy of gamma-rays. DNA damage and DNA damage removal were measured using the gamma-H2AX foci assay. Lymphocytes from one donor and the nuclear antigen H2B were used as a positive control to test the staining protocol. RESULTS: In the absence of radiation exposure, no significant differences for both H2B and gamma-H2AX signals were detected when comparing buccal cells and lymphocytes. The gamma-H2AX foci rate per cell in non-irradiated buccal cells was 0.08 +/- 0.02. The number of gamma-H2AX foci increased linearly with ionising radiation dose in the interval from 0-4 Gy, and reached a foci rate per cell of 0.82 +/- 0.22 at 4 Gy. Incubation experiments after in vitro gamma irradiation revealed that the number of gamma-H2AX foci did not show a significant decrease 5 h post exposure under the experimental conditions used. CONCLUSION: Data suggest that it is possible to apply the gamma-H2AX foci assay for the detection of ionising radiation-induced DNA damage in buccal exfoliated cells. The low removal of ionising radiation induced gamma-H2AX foci in buccal cells is a potential advantage for a biological dosimetry application.

Noninvasive radiation burn diagnosis using speckle phenomenon with a fractal approach to processing.

Radiation burns account for the vast majority of damage by accidental radiation exposure. They are characterized by successive and unpredictable inflammatory bursts that are preceded by a clinically latent postirradiation period. Diagnosis and prognosis of the clinical course of radiation burns have proven to be a difficult task. In a classical clinical setting, no technique can distinguish irradiated versus healthy skin during the clinically latent period, hence development of new tools is required. This work describes a noninvasive technique based on speckle phenomenon, designed to support radiation burn diagnosis and prognosis. Speckle produced by strongly scattering media contains information about their optical properties. The difficulty is to extract significant information from speckle patterns to discriminate between strongly scattering media and to characterize any change. Speckle patterns from irradiated and nonirradiated porcine skins are recorded in vivo several times after radiation exposure. A fractal approach is used in the treatment of speckle patterns. The results show that this technique allows discrimination between healthy and irradiated skin, in particular during the clinically latent period (p<0.01). Parameters extracted from speckle patterns discriminate and vary differently with radiation, which means they represent different information about skin changes.

Cell response to ionising radiation analysed by gene expression patterns.

Following ionising radiation exposure of living cells several mechanisms are activated through gene modulations. The measurement of these modifications can be done with QT-PCR and, since about 10 years, microarray technique. The latter approach has the advantage to allow a global monitoring of the complex cellular responses to radiation-induced stress and has been proposed to be used for dose assessment. Even if some publications have identified sets of genes specific to given doses, and that some of the genes have an induction proportional to the dose, a precise estimation of the received dose seems difficult with gene expression, at least in the near future. Nevertherless, in vivo studies have shown that gene profiles of individuals chronically exposed to a cumulative dose of more than 10 mSv are significantly modified. This highlights the great potential of microarray approaches in the detection of low dose exposure.

Initial evaluation and follow-up of acute radiation syndrome in two patients from the Dakar accident.

The aim of this work was to evaluate and follow up the evolution of radiation damage in two victims of a radiation accident. Blood samples were used for cytogenetic evaluation of radiation dose and heterogeneity. The radiation dose estimates were 1 Gy and 2.3 Gy in the two most exposed patients. Plasma was used for the measurement of the Flt3 ligand as a marker of haematopoietic aplasia, citrulline for damage to the jejunal mucosal epithelium and oxysterols for damage to the liver, the central nervous system and the vascular compartment. The use of these biological indicators demonstrated the presence of a haematopoietic syndrome and suggested the presence of subclinical radiation-induced damage to the liver in one of the two patients. These results support the interest in using these biological indicators in order to evaluate radiation damage, especially in complex accidental situations.

Broad modulation of gene expression in CD4+ lymphocyte subpopulations in response to low doses of ionizing radiation.

To compare the responses of the different lymphocyte subtypes after an exposure of whole blood to low doses of ionizing radiation, we examined variations in gene expression in different lymphocyte subpopulations using microarray technology. Blood samples from five healthy donors were independently exposed to 0 (sham irradiation), 0.05 and 0.5 Gy of ionizing radiation. Three and 24 h after exposure, CD56+, CD4+ and CD8+ cells were negatively isolated. RNA from each set of experimental conditions was competitively hybridized on 25k oligonucleotide microarrays. Modifications of gene expression were measured after both intervals and in all cell types. Twenty-four hours after exposure to 0.5 Gy, we observed an induction of the expression of BAX, PCNA, GADD45, DDB2 and CDKN1A. However, the numbers of modulated genes greatly differed between cell types. In particular, 3 h after exposure to doses as low as 0.05 Gy, the number of down-modulated genes was 10 times greater for CD4+ cells than for all other cell types. Moreover, most of these repressed genes were taking part in the cell processes of protein biosynthesis and oxidative phosphorylation. The results suggest that several biological pathways in CD4+ cells could be sensitive to low doses of radiation. Therefore, specifically studying CD4+ cells could help to understand the mechanisms involved in low-dose response and allow their detection.

International study of factors affecting human chromosome translocations.

Chromosome translocations in peripheral blood lymphocytes of normal, healthy humans increase with age, but the effects of gender, race, and cigarette smoking on background translocation yields have not been examined systematically. Further, the shape of the relationship between age and translocation frequency (TF) has not been definitively determined. We collected existing data from 16 laboratories in North America, Europe, and Asia on TFs measured in peripheral blood lymphocytes by fluorescence in situ hybridization whole chromosome painting among 1933 individuals. In Poisson regression models, age, ranging from newborns (cord blood) to 85 years, was strongly associated with TF and this relationship showed significant upward curvature at older ages versus a linear relationship (p<0.001). Ever smokers had significantly higher TFs than non-smokers (rate ratio (RR)=1.19, 95% confidence interval (CI), 1.09-1.30) and smoking modified the effect of age on TFs with a steeper age-related increase among ever smokers compared to non-smokers (p<0.001). TFs did not differ by gender. Interpreting an independent effect of race was difficult owing to laboratory variation. Our study is three times larger than any pooled effort to date, confirming a suspected curvilinear relationship of TF with age. The significant effect of cigarette smoking has not been observed with previous pooled studies of TF in humans. Our data provide stable estimates of background TF by age, gender, race, and smoking status and suggest an acceleration of chromosome damage above age 60 and among those with a history of smoking cigarettes.