The incidence of unstable chromosome aberrations in peripheral blood lymphocytes from unirradiated and occupationally exposed people

Biodose Tools: an R shiny application for biological dosimetry

INTRODUCTION

In the event of a radiological accident or incident, the aim of biological dosimetry is to convert the yield of a specific biomarker of exposure to ionizing radiation into an absorbed dose. Since the 1980s, various tools have been used to deal with the statistical procedures needed for biological dosimetry, and in general those who made several calculations for different biomarkers were based on closed source software. Here we present a new open source program, Biodose Tools, that has been developed under the umbrella of RENEB (Running the European Network of Biological and retrospective Physical dosimetry).

MATERIALS AND METHODS

The application has been developed using the R programming language and the shiny package as a framework to create a user-friendly online solution. Since no unique method exists for the different mathematical processes, several meetings and periodic correspondence were held in order to reach a consensus on the solutions to be implemented.

RESULTS

The current version 3.6.1 supports dose-effect fitting for dicentric and translocation assay. For dose estimation Biodose Tools implements those methods indicated in international guidelines and a specific method to assess heterogeneous exposures. The app can include information on the irradiation conditions to generate the calibration curve. Also, in the dose estimate, information about the accident can be included as well as the explanation of the results obtained. Because the app allows generating a report in various formats, it allows traceability of each biological dosimetry study carried out. The app has been used globally in different exercises and training, which has made it possible to find errors and improve the app itself. There are some features that still need consensus, such as curve fitting and dose estimation using micronucleus analysis. It is also planned to include a package dedicated to interlaboratory comparisons and the incorporation of Bayesian methods for dose estimation.

CONCLUSION

Biodose Tools provides an open-source solution for biological dosimetry laboratories. The consensus reached helps to harmonize the way in which uncertainties are calculated. In addition, because each laboratory can download and customize the app's source code, it offers a platform to integrate new features.

The Imaging Flow Cytometry-Based Cytokinesis-Block MicroNucleus (CBMN) Assay

The dose of ionizing radiation received by an individual can be determined using biodosimetry methods which measure biomarkers of exposure in tissue samples from that individual. These markers can be expressed in many ways, including DNA damage and repair processes. Following a mass casualty event involving radiological or nuclear material, it is important to rapidly provide this information to medical responders to assist in the medical management of potentially exposed casualties. Traditional methods of biodosimetry rely on microscope analysis, making them time-consuming and labor-intensive. To increase sample throughput following a large-scale radiological mass casualty event, several biodosimetry assays have been adapted for analysis by imaging flow cytometry. This chapter briefly reviews these methods with a focus on the most current methodology to identify and quantify micronuclei in binucleated cells within the cytokinesis-block micronucleus assay using an imaging flow cytometer.

Background Level of Unstable Chromosome Aberrations in the Kazakhstan Population: A Human Biomonitoring Study

Kazakhstan is known as a country with a complex radioecological situation resulting from different sources such as a natural radiation background, extensive activities of the industrial system of the former Soviet Union and a well-known testing of nuclear power weapons occurred in the Semipalatinsk Test Site (STS) area. The present study focuses on the assessment of the background of dicentric chromosomes in Kazakhstan’s population, which is the starting point in the dose assessment of irradiated people, since the baseline level of spontaneous dicentrics can vary significantly in different populations. In this context, aiming to determine the background frequency of chromosome aberrations in the population of Kazakhstan, considering the heterogeneity of natural radiation background levels of its large territory, a selection of 40 control subjects living in four cities of North, South, West and East Kazakhstan was performed. The cytogenetic study on the selected groups showed fairly low background frequency values of chromosome aberrations (0.84 ± 0.83 per 1000 cells), comparable with other data in the literature on general populations, reporting background frequency values between 0.54 and 2.99 per 1000 cells. The obtained results should be taken into account when constructing the dose–effect calibration curve used in cytogenetic biodosimetry, as a “zero” dose point, which will reduce the uncertainty in quantifying the individual absorbed dose in emergency radiological situations.

Chromosome aberration dynamics in breast cancer patients treated with radiotherapy: Implications for radiation biodosimetry

Although radiological accidents often result in partial-body radiation exposure, most biodosimetry studies focus on estimating whole-body exposure doses. We have evaluated time-dependent changes in chromosomal aberrations before, during, and after localized fractionated radiotherapy. Twelve patients with carcinoma in situ of the breast who underwent identical adjuvant radiation therapy (50 Gy in 25 fractions) were included in the study. Lymphocytes were collected from patients before, during, and after radiotherapy, to measure chromosome aberrations, such as dicentric chromosomes and translocations. Chromosome aberrations were then used to calculate whole- and partial-body biological absorbed doses of radiation. Dicentric chromosome frequencies in all study participants increased during radiotherapy (p < 0.05 in Kruskal-Wallis test). Increases of translocation frequencies during radiotherapy were observed in seven of the twelve patients. The increased levels of dicentric chromosomes and translocations persisted throughout our 1-year follow-up, and evidence of partial-body exposure (such as Papworth's U-value > 1.96) was observed more than 1 year after radiotherapy. We found that cytogenetic biomarkers reflected partial-body fractionated radiation exposure more than 1 year post-exposure. Our findings suggest that chromosome aberrations can be used to estimate biological absorbed radiation doses and can inform medical intervention for individuals suspected of fractionated or partial-body radiation exposure.

Translocation dose-response curve for 137Cs γ-rays: Dose validation at various dose rate and changing dose rate conditions

A Fluorescence In-Situ Hybridization (FISH) based translocation dose-response curve has been constructed for biodosimetry application in our nuclear establishment at Kalpakkam, India. Peripheral blood sample from a healthy male donor (27 years) was exposed to nine different doses (0.1 Gy-5 Gy) of ¹³⁷Cs γ-rays (100 mGy/min) in an automated calibration facility with a linear distancing system and subjected to FISH assay using chromosome 1, 2 and 4 specific fluorescent probes. Validation of the dose-response curve was done following three different approaches i) by blind test method ii) using blood samples exposed to γ doses (0.5, 1 & 2 Gy) at different dose rates (124, 23 & 10 mGy/min) and iii) with blood samples exposed to 0.5, 1 & 2 Gy γ doses at changing dose rates (increasing and decreasing dose rates). Results showed that a predefined dose-response curve constructed at a particular acute dose rate can be used for dose estimation in exposures involving varying dose rates and changing dose rate scenarios.

Cytogenetic monitoring of peripheral blood lymphocytes from medical radiation professionals occupationally exposed to low-dose ionizing radiation

In order to assess the health risk of low-dose radiation to radiation professionals, monitoring is performed through chromosomal aberration analysis and micronuclei (MN) analysis. MN formation has drawbacks for monitoring in the low-dose range. Nucleoplasmic bridge (NPB) analysis, with a lower background level, has good dose-response relationships at both high and relatively low dose ranges. Dicentric and ring chromosomes were analyzed in 199 medical radiation professionals, and NPB/MN yields were analyzed in 205 radiation professionals. The effects of sex, age of donor, types of work, and length of service on these cytogenetic endpoints were also analyzed. The yields of the three cytogenetic endpoints were significantly higher in radiation professionals versus controls. Frequencies of dicentric plus ring chromosomes were affected by length of service. NPB frequencies were influenced by type of work and length of service. MN yields were affected not only by types of work and length of service but also by donor sex and age. In conclusion, dicentric plus ring chromosomes, NPB, and MN can be induced by low-dose radiation in radiation professionals. NPB is a potential biomarker to assess the health risk of occupational low-dose radiation exposure.

Automated Cytogenetic Biodosimetry at Population-Scale

The dicentric chromosome (DC) assay accurately quantifies exposure to radiation; however, manual and semi-automated assignment of DCs has limited its use for a potential large-scale radiation incident. The Automated Dicentric Chromosome Identifier and Dose Estimator (ADCI) software automates unattended DC detection and determines radiation exposures, fulfilling IAEA criteria for triage biodosimetry. This study evaluates the throughput of high-performance ADCI (ADCI-HT) to stratify exposures of populations in 15 simulated population scale radiation exposures. ADCI-HT streamlines dose estimation using a supercomputer by optimal hierarchical scheduling of DC detection for varying numbers of samples and metaphase cell images in parallel on multiple processors. We evaluated processing times and accuracy of estimated exposures across census-defined populations. Image processing of 1744 samples on 16,384 CPUs required 1 h 11 min 23 s and radiation dose estimation based on DC frequencies required 32 sec. Processing of 40,000 samples at 10 exposures from five laboratories required 25 h and met IAEA criteria (dose estimates were within 0.5 Gy; median = 0.07). Geostatistically interpolated radiation exposure contours of simulated nuclear incidents were defined by samples exposed to clinically relevant exposure levels (1 and 2 Gy). Analysis of all exposed individuals with ADCI-HT required 0.6–7.4 days, depending on the population density of the simulation.

Establishing a Reference Dose-Response Calibration Curve for Dicentric Chromosome Aberrations to Assess Accidental Radiation Exposure in Saudi Arabia

In cases of nuclear and radiological accidents, public health and emergency response need to assess the magnitude of radiation exposure regardless of whether they arise from disaster, negligence, or deliberate act. Here we report the establishment of a national reference dose–response calibration curve (DRCC) for dicentric chromosome (DC), prerequisite to assess radiation doses received in accidental exposures. Peripheral blood samples were collected from 10 volunteers (aged 20–40 years, median = 29 years) of both sexes (three females and seven males). Blood samples, cytogenetic preparation, and analysis followed the International Atomic Energy Agency EPR-Biodosimetry 2011 report. Irradiations were performed using 320 kVp X-rays. Metafer system was used for automated and assisted (elimination of false-positives and inclusion of true-positives) metaphases findings and DC scoring. DC yields were fit to a linear–quadratic model. Results of the assisted DRCC showed some variations among individuals that were not statistically significant (homogeneity test, P = 0.66). There was no effect of age or sex (P > 0.05). To obtain representative national DRCC, data of all volunteers were pooled together and analyzed. The fitted parameters of the radiation-induced DC curve were as follows: Y = 0.0020 (±0.0002) + 0.0369 (±0.0019) ^*D + 0.0689 (±0.0009) ^*D². The high significance of the fitted coefficients (z-test, P < 0.0001), along with the close to 1.0 p-value of the Poisson-based goodness of fit (χ² = 3.51, degrees of freedom = 7, P = 0.83), indicated excellent fitting with no trend toward lack of fit. The curve was in the middle range of DRCCs published in other populations. The automated DRCC over and under estimated DCs at low (<1 Gy) and high (>2 Gy) doses, respectively, with a significant lack of goodness of fit (P < 0.0001). In conclusion, we have established the reference DRCC for DCs induced by 320 kVp X-rays. There was no effect of age or sex in this cohort of 10 young adults. Although the calibration curve obtained by the automated (unsupervised) scoring misrepresented dicentric yields at low and high doses, it can potentially be useful for triage mode to segregate between false-positive and near 2-Gy exposures from seriously irradiated individuals who require hospitalization.

Cytogenetic follow-up of an individual after accidental exposure to industrial radiation using dicentric frequency in blood lymphocytes

A radiation accident occurred in Bursa, Turkey, in July 2005. An industrial radiographer was exposed to industrial iridium-192 gamma rays for 5 h while laying the natural gas line. After 5 h, the victim had a break because of vomiting and nausea. He ended his work, considering that he might have been exposed to radiation. In a few days, erythema, pain, desquamation, edema started in both hands of the victim. The biological dose assessment was started based on frequencies of dicentrics and rings in peripheral blood lymphocytes ten days after the radiation accident. 6 repeated blood samples were taken for 9 years and analyzed staining after giemsa. After 9 years, decline at dicentric frequencies is significant, but still, dicentric contain cells were detected, which were a strong indicator for external radiation exposure.

Estimating partial-body ionizing radiation exposure by automated cytogenetic biodosimetry

PURPOSE

Inhomogeneous exposures to ionizing radiation can be detected and quantified with the dicentric chromosome assay (DCA) of metaphase cells. Complete automation of interpretation of the DCA for whole-body irradiation has significantly improved throughput without compromising accuracy, however, low levels of residual false positive dicentric chromosomes (DCs) have confounded its application for partial-body exposure determination.

MATERIALS AND METHODS

We describe a method of estimating and correcting for false positive DCs in digitally processed images of metaphase cells. Nearly all DCs detected in unirradiated calibration samples are introduced by digital image processing. DC frequencies of irradiated calibration samples and those exposed to unknown radiation levels are corrected subtracting this false positive fraction from each. In partial-body exposures, the fraction of cells exposed, and radiation dose can be quantified after applying this modification of the contaminated Poisson method.

RESULTS

Dose estimates of three partially irradiated samples diverged 0.2-2.5 Gy from physical doses and irradiated cell fractions deviated by 2.3%-15.8% from the known levels. Synthetic partial-body samples comprised of unirradiated and 3 Gy samples from 4 laboratories were correctly discriminated as inhomogeneous by multiple criteria. Root mean squared errors of these dose estimates ranged from 0.52 to 1.14 Gy² and from 8.1 to 33.3%² for the fraction of cells irradiated.

CONCLUSIONS

Automated DCA can differentiate whole- from partial-body radiation exposures and provides timely quantification of estimated whole-body equivalent dose.

Radiation Biomarkers in Large Scale Human Health Effects Studies

Following recent developments, the RENEB network (Running the European Network of biological dosimetry and physical retrospective dosimetry) is in an excellent position to carry out large scale molecular epidemiological studies of ionizing radiation effects, with validated expertise in the dicentric, fluorescent in situ hybridization (FISH)-translocation, micronucleus, premature chromosome condensation, gamma-H2AX foci and gene expression assays. Large scale human health effects studies present complex challenges such as the practical aspects of sample logistics, assay costs, effort, effect modifiers and quality control/assurance measures. At Public Health England, the dicentric, automated micronucleus and gamma-H2AX radiation-induced foci assays have been tested for use in a large health effects study. The results of the study and the experience gained in carrying out such a large scale investigation provide valuable information that could help minimise random and systematic errors in biomarker data sets for health surveillance analyses going forward.

A faster and easier biodosimetry method based on calyculin A-induced premature chromosome condensation (PCC) by scoring excess objects

Dicentric analysis and the ring PCC assay as established biodosimetry methods both have limitations in the estimation of absorbed doses in suspected overexposure cases between 5 and 10 Gy. The proposed method based on calyculin A-induced PCC overcomes these limitations by scoring excess objects as the endpoint. This new scoring method can potentially serve as a faster and up-scalable approach that complements the existing methods with higher accuracy at different dose ranges. It can also potentially be performed by less skilled workers when no automated system is available in mass casualty emergency cases to assist with the triage of patients. Additionally, it offers the possibility to further reduce the sample size and PCC induction time. In this pilot study, a calibration curve for excess objects was constructed using the new scoring method for the first time and a blind validation test composed of three unknown doses was carried out. Almost all the dose estimates were within the 95% confidence limits of the actual test doses by scoring only 50-100 PCC spreads. This method was found to be more accurate than ring PCC for doses below 10 Gy.

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.

Radioprotective efficacy of plastic polymer against the toxicogenomic effects of radiopharmaceutical 18F-FDG on human lymphocytes

BACKGROUND

Healthcare workers occupationally exposed to 18F-FDG cannot wear protective equipment, such as lead aprons, since the interaction between high energy radiation (511 keV) and metal increases the dose of radiation absorption. The objective of this study was to evaluate the shielding efficacy of a plastic polymer against the toxicogenomic effects of ionizing radiation in human lymphocytes, using cytokinesis-block micronucleus assays.

METHODS

Human peripheral blood lymphocytes were isolated from three subjects and cultured under standard conditions. The cultures were exposed to 300 mCi of 18F-FDG at a distance of 10 cm for 10 min, in the absence of shielding or with lead, polymer, and lead + polymer shields.

RESULTS

Lead shielding was found to increase the number of counts detected by Geiger-Müller radiation monitors as a consequence of the photoelectron effect. Conversely, the lead + polymer shield reduced the number of counts. The lead, polymer, and lead + polymer shields significantly reduced the frequency of micronuclei, nucleoplasmic bridges, and nuclear buds induced by ionizing radiation. Regarding cytotoxicity, only the lead + polymer shield re-established the cell cycle at the level observed for the negative control.

CONCLUSIONS

Lead aprons that are internally coated with polymer increased the radiological protection of individuals occupationally exposed to 18F-FDG PET/CT, especially during examinations.

Cytogenetic Analysis After Temporary Residence in the Area of the Uncontrolled Ruthenium-106 Release in Russia in September 2017

In September and October 2017, elevated atmospheric ruthenium contamination was measured in several European countries. The most probable origin of this release of radionuclides was reconstructed to be the Southern Ural region. During that time, five workers from a German company stayed up to 2 wk about 120 km from the Chelyabinsk region in Ekaterinburg, Russia. No clinical symptoms were reported during or after the suspected radiation exposure, and no internal contamination was found in whole-body measurements. However, to investigate radiation protection issues and to clarify the workers' situation in order to reassure them, as they planned to continue working in Ekaterinburg, our laboratory was urgently requested by the company's occupational physician to perform biodosimetry using dicentric analysis to determine if the workers have been exposed to radiation by incorporation of radionuclides. The workers' dicentric yields have been compared to reference data of background frequencies in unexposed individuals, but, as it is not reasonable to quantify individual absorbed radiation doses from internalized beta emitters due to various confounding factors, individual dose estimation has not been performed. Dicentric frequencies for two workers differed significantly from the mean laboratory background level, which could have been induced by an exposure to incorporated radionuclides due to beta emissions by Ru or to gamma irradiation by the decay nuclide of Ru. However, the maximum absorbed radiation doses calculated for a resident in the Ru-contaminated area during that time does not correspond to the observed dicentric frequencies. It cannot be excluded that their dicentric frequencies were already elevated before September 2017, potentially induced by an earlier radiation exposure to diagnostic x rays or even by chance.

What does radiation biology tell us about potential health effects at low dose and low dose rates?

The health risks to humans exposed to low dose and low dose rate ionising radiation remain ambiguous and are the subject of debate. The need to establish risk assessment standards based on the mechanisms underlying low dose/low fluence radiation exposures has been recognised by scholarly and regulatory bodies as critical for reducing the uncertainty in predicting adverse health risks of human exposure to low doses of radiation. Here, a brief review of laboratory-based evidence of molecular and biochemical changes induced by low doses and low dose rates of radiation is presented. In particular, two phenomena, namely bystander effects and adaptive responses that may impact low-level radiation health risks, are discussed together with the need for further studies. The expansion of this knowledge by considering the important variables that affect the radiation response (e.g. genetic susceptibility, time after exposure), and using the latest advances in experimental models and bioinformatics tools, may guide epidemiological studies towards reducing the uncertainty in predicting the potential health hazards of exposure to low-dose radiation.

Chronic low dose exposure of hospital workers to ionizing radiation leads to increased micronuclei frequency and reduced antioxidants in their peripheral blood lymphocytes

Purpose: The regular low dose occupational exposure to ionizing radiation may induce deleterious health effects, which may be of particular interest to medical radiation workers who daily handle X-ray machines. Human peripheral blood lymphocytes are able to retain the signature of radiation-induced DNA damage, therefore, the present study was undertaken to investigate the DNA damage and antioxidants status in hospital workers occupationally exposed to low doses of X-rays. Materials and methods: The peripheral blood lymphocytes of the occupationally exposed and control groups matched for age, gender, tobacco usage, and alcohol consumption were cultured and micronuclei frequency was determined. Activities of antioxidant enzymes and lipid peroxidation were also estimated in their plasma. Results: The micronuclei frequency in the occupationally exposed group (n = 33), increased significantly (p < .0001) followed by reduced glutathione-s-transferase (p < .01) and catalase (p < .001) activities, and increased lipid peroxidation (p < .05) when compared to the control group (n = 33). Occupational exposure resulted in an effective dose ranging between 3.14 to 144.5 mSv (40.88 ± 39.86mSv) depending on the employment duration of 3-29 years (10.33 ± 7.05 years). A correlation between the micronuclei frequency (p < .05) and catalase activity (p < .05) existed in the occupationally exposed individuals depending on the smoking habit, age, duration of employment, cumulative exposure dose and number of patients handled per day. Conclusions: We have observed that protracted low dose exposure to ionizing radiation is an inevitable occupational hazard leading to persistence of oxidative stress and increased genomic instability in the radiological technicians depending on the time spent with X-rays, cumulative dose received and the number of patients handled daily raising the risk of cancer development.

The Application of Imaging Flow Cytometry to High-Throughput Biodosimetry

Biodosimetry methods, including the dicentric chromosome assay, the cytokinesis-block micronucleus assay and the γH2AX marker of DNA damage are used to determine the dose of ionizing radiation. These techniques are particularly useful when physical dosimetry is absent or questioned. While these assays can be very sensitive and specific, the standard methods need to be adapted to increase sample throughput in the case of a large-scale radiological/nuclear event. Recent modifications to the microscope-based assays have resulted in some increased throughput, and a number of biodosimetry networks have been, and continue to be, established and strengthened. As the imaging flow cytometer (IFC) is a technology that can automatically image and analyze processed blood samples for markers of radiation damage, the microscope-based biodosimetry techniques can be modified for the IFC for high-throughput biological dosimetry. Furthermore, the analysis templates can be easily shared between networked biodosimetry laboratories for increased capacity and improved standardization. This review describes recent advances in IFC methodology and their application to biodosimetry.

Biodosimetry of Persons Chronically Exposed to Low and Therapeutic Doses of Ionizing Radiation

Dynamic changes of the chromosomal aberrations and the DNA damage were analyzed in individuals exposed to low and therapeutic doses of radiation. The investigation included 37 persons living in areas where the radioactive sources were discovered 10–12 years ago. It was established by biodosimetry methods that the examined persons had absorbed dose of 0.2–0.7 Gy or had increased number of chromosomal aberrations, though insufficient to determine a dose. Clinical examination, chromosomal analysis, and assay of DNA damage by the comet (single-cell gel electrophoresis) assay were carried out. There was no correlation between the doses received 10 years ago and the cytogenetic changes with clinical outcome. The effect of the local fractionated gamma-irradiation with doses of 40–70 Gy was studied in cancer patients with localized head and neck tumors. The study of chromosomal abnormalities, the DNA damages by the comet assay, and the micronuclei detection of the buccal cells revealed a statistically significant correlation between the initial cytogenetic indices in cancer patients and their dynamic changes during and after the radiation exposure. In addition, the correlation was detected between the initial cytogenetic parameters and the functional stage of red blood system. Our results allow us to conclude that there is a need for further research to estimate the individual radiation risk to optimize and individualize the subsequent medical management of radiotherapy.

Retrospective Biodosimetry of an Occupational Overexposure-Case Study

In 2014, Health Canada was approached by the Canadian Nuclear Safety Commission to conduct biodosimetry for a possible overexposure 4 y prior to assessment. Dose estimates were determined by means of two cytogenetic assays, the dicentric chromosome assay (DCA) and translocations as measured by the fluorescent in situ hybridization (FISH). As dicentrics are considered to be unstable over time, the results of the DCA were adjusted to account for the time elapsed between the suspected exposure and sampling. The frequency of damage was then compared to Health Canada's calibration curves, respectively, to calculate dose. In addition, the translocation data were corrected for age-related increases in background. With a half-life of 36 months for dicentric chromosomes taken into consideration, the dose estimates from both assays were in agreement. Due to the uncertainty in the half-life of dicentrics, the FISH assay is considered to be more reliable as a technique for retrospective biodosimetry.

Management of ionizing radiation injuries and illnesses, Part 3: Radiobiology and health effects of ionizing radiation

Ionizing radiation exposure can induce profound changes in intracellular components, potentially leading to diverse health effects in exposed individuals. Any cellular component can be damaged by radiation, but some components affect cellular viability more profoundly than others. The ionization caused by radiation lasts longer than the initial inciting incident, continuing as 1 ionization incident causes another. In some cases, damage to DNA can lead to cellular death at mitosis. In other cases, activation of the genetic machinery can lead to a genetic cascade potentially leading to mutations or cell death by apoptosis. In the third of 5 articles on the management of injuries and illnesses caused by ionizing radiation, the authors provide a clinically relevant overview of the pathophysiologic process associated with potential exposure to ionizing radiation.

Establishing cytogenetic biodosimetry laboratory in Saudi Arabia and producing preliminary calibration curve of dicentric chromosomes as biomarker for medical dose estimation in response to radiation emergencies

In cases of public or occupational radiation overexposure and eventual radiological accidents, it is important to provide dose assessment, medical triage, diagnoses and treatment to victims. Cytogenetic bio-dosimetry based on scoring of dicentric chromosomal aberrations assay (DCA) is the “gold standard” biotechnology technique for estimating medically relevant radiation doses. Under the auspices of the National Science, Technology and Innovation Plan in Saudi Arabia, we have set up a biodosimetry laboratory and produced a national standard dose–response calibration curve for DCA, pre-required to estimate the doses received. For this, the basic cytogenetic DCA technique needed to be established. Peripheral blood lymphocytes were collected from four healthy volunteers and irradiated with radiation doses between 0 and 5 Gy of 320 keV X-rays. Then, lymphocytes were PHA stimulated, Colcemid division arrested and stained cytogenetic slides were prepared. The Metafer4 system (MetaSystem) was used for automatic and manually assisted metaphase finding and scoring of dicentric chromosomes. Results were fit to the linear-quadratic dose–effect model according to the IAEA EPR-Biodosimetry-2011 report. The resulting manually assisted dose–response calibration curve (Y = 0.0017 + 0.026 × D + 0.081 × D²) was in the range of those described in other populations. Although the automated scoring over-and-under estimates DCA at low (<1 Gy) and high (>2 Gy) doses, respectively, it showed potential for use in triage mode to segregate between victims with potential risk to develop acute radiotoxicity syndromes. In conclusion, we have successfully established the first biodosimetry laboratory in the region and have produced a preliminary national dose–response calibration curve. The laboratory can now contribute to the national preparedness plan in response to eventual radiation emergencies in addition to providing information for decision makers and public health officials who assess the magnitude of public, medical, occupational and accidental radiation exposures.

Cytogenetic monitoring of nuclear workers occupationally exposed to ionising radiation

Chromosome aberration (CA) analysis using Giemsa techniques was performed in blood lymphocytes of 84 nuclear workers with cumulative doses of 1-632 mSv during employment periods of 1-25 y. The control group comprised 82 healthy male donors. An estimated CA frequency in the total radiation-exposed group was significantly higher when compared with the controls (2.27 vs. 1.76 CA/100 cells, p < 0.05). CA analyses revealed no significant differences between workers with external gamma radiation exposure and the controls (1.60 vs. 1.76 CA/100 cells, p > 0.05). However, significant increase in the total CA frequency was determined in workers with additional internal exposure (2.54 CA/100 cells, p < 0.05) and those with registered neutron doses (2.95 CA/100 cells, p < 0.01). No correlation was found between CA frequency and occupational exposure dose. Borderline significant correlation was found between duration of employment and total CA (r = 0.218, p = 0.046, Fig. 2) and chromosome-type aberration (r = 0.265, p = 0.015) frequency.

Biodosimetry of restoration workers for the Tokyo Electric Power Company (TEPCO) Fukushima Daiichi nuclear power station accident

The biological dose of nuclear workers engaged in emergency response tasks at Tokyo Electric Power Company (TEPCO) Fukushima Daiichi Nuclear Power Station was estimated in the present study. As the national core center for radiation emergency medical preparedness in Japan, the National Institute of Radiological Sciences (NIRS) received all individuals who were suspected of being overexposed to acute radiation. In the course of health examinations at NIRS, biological dosimetry was performed by the dicentric chromosome assay (DCA). Twelve individuals were examined from 21 March-1 July 2011. The results indicated that the estimated exposure doses for all individuals were lower than 300 mGy, with the mean value of about 101 mGy. These results by DCA were in accordance with those obtained by physical dosimetry based on personal dosimeter recording assessment. The results corroborate the fact that no acute radiation syndrome was observed among the workers examined.

Analysis of chromosome damage for biodosimetry using imaging flow cytometry

The dicentric chromosome assay (DCA), which involves counting the frequency of dicentric chromosomes in mitotic lymphocytes and converting it to a dose-estimation for ionizing radiation exposure, is considered to be the gold standard for radiation biodosimetry. Furthermore, for emergency response, the DCA has been adapted for triage by simplifying the scoring method [1]. With the development of new technologies such as the imaging flow cytometer, it may now be possible to adapt this microscope-based method to an automated cytometry method. This technology allows the sensitivity of microscopy to be maintained while adding the increased throughput of flow cytometry. A new protocol is being developed to adapt the DCA to the imaging cytometer in order to further increase the rapid determination of a biological dose. Peripheral blood mononuclear cells (PBMC) were isolated from ex vivo irradiated whole blood samples using a density gradient separation method and cultured with PHA and Colcemid. After 48h incubation, the chromosomes were isolated, stained for DNA content with propidium iodide (PI) and labelled with a centromere marker. Stained chromosomes were then analyzed on the ImageStream(×) (EMD-Millipore, Billerica, MA). Preliminary results indicate that individual chromosomes can be identified and mono- and dicentric chromosomes can be differentiated by imaging cytometry. A dose response curve was generated using this technology. The details of the method and the dose response curve are presented and compared to traditional microscope scoring. Imaging cytometry is a new technology which enables the rapid, automated analysis of fluorescently labelled chromosomes. Adapting the dicentric assay to this technology has the potential for high throughput analysis for mass casualty events.

Cytogenetic dose-response in vitro for biological dosimetry after exposure to high doses of gamma-rays

The dose response for dicentrics plus centric rings and total unstable chromosome-type aberrations was studied in the first mitoses of cultured human peripheral blood lymphocytes irradiated in vitro to doses of ∼2, 4, 6, 8, 10, 16 and 20 Gy of acute (60)Со gamma-rays. A dose-dependent increase of aberration yield was accompanied by a tendency to the underdispersion of dicentrics and centric rings among cells distributions compared with Poisson statistics at doses ≥6 Gy. The formal fitting of the data to a linear-quadratic model resulted in an equation with the linear and quadratic coefficients ranged 0.098-0.129×cell(-1)×Gy(-1) and 0.039-0.034×cell(-1)×Gy(-2), respectively, depending on the fitting method. The actual radiation-induced aberration yield was markedly lower than expected from a calibration curve, generated earlier within a lower dose range. Interlaboratory variations in reported dicentric yields induced by medium-to-high radiation doses in vitro are discussed.

Dose-rate effects and dose and dose-rate effectiveness factor on frequencies of chromosome aberrations in splenic lymphocytes from mice continuously exposed to low-dose-rate gamma-radiation

Dose-rate effects on chromosome aberrations in the low-dose-rate range have not been evaluated previously. The incidences of chromosome aberrations were analysed in splenic lymphocytes from female specific pathogen-free (SPF) C3H mice that were continuously irradiated with low- or medium-dose-rate (LDR, MDR) (137)Cs γ rays from 56 days of age to evaluate the dose-rate effects. The dose-response relationship for the frequency of dicentric chromosome aberration at each dose rate (400 mGy/22h/day, 20 mGy/22h/day and 1 mGy/22h/day) was obtained using age-adjusted multiple linear regression analysis assuming that the relationship can be represented by a linear or linear quadratic model and a test for the difference between the irradiated group and the non-irradiated group. Values of the linear term, shown as the slope, decreased as the dose rate was reduced from 400 mGy/22h/day (18.2 mGy h(-1)) to 1 mGy/22h/day (0.045 mGy h(-1)), indicating a positive dose-rate effect in the dose-rate region. The incidences of dicentric chromosomes and translocation for LDR (20 mGy day(-1)) were compared with those for HDR (890 mGy min(-1)) irradiation at each total dose to obtain the dose and dose-rate effectiveness factor (DDREF). The DDREFs were 4.5 for dicentrics and 2.3 for translocations at a total dose of 100 mGy based on the chromosome aberration rate. These results will be useful for estimating the risk of LDR radiation exposure and radiation protection.

Chromosome damage and cell proliferation rates in in vitro irradiated whole blood as markers of late radiation toxicity after radiation therapy to the prostate

PURPOSE

In vitro irradiated blood samples from prostate cancer patients showing late normal tissue damage were examined for lymphocyte response by measuring chromosomal aberrations and proliferation rate.

METHODS AND MATERIALS

Patients were selected from a randomized trial evaluating the optimal timing of dose-escalated radiation and short-course androgen deprivation therapy. Of 438 patients, 3% experienced grade 3 late radiation proctitis and were considered to be radiosensitive. Blood samples were taken from 10 of these patients along with 20 matched samples from patients with grade 0 proctitis. The samples were irradiated at 6 Gy and, along with control samples, were analyzed for dicentric chromosomes and excess fragments per cell. Cells in first and second metaphase were also enumerated to determine the lymphocyte proliferation rate.

RESULTS

At 6 Gy, there were statistically significant differences between the radiosensitive and control cohorts for 3 endpoints: the mean number of dicentric chromosomes per cell (3.26 ± 0.31, 2.91 ± 0.32; P=.0258), the mean number of excess fragments per cell (2.27 ± 0.23, 1.43 ± 0.37; P<.0001), and the proportion of cells in second metaphase (0.27 ± 0.10, 0.46 ± 0.09; P=.0007).

CONCLUSIONS

These results may be a valuable indicator for identifying radiosensitive patients and for tailoring radiation therapy.

The micronucleus assay as a biological dosimeter in hospital workers exposed to low doses of ionizing radiation

The health risk associated with low levels of ionizing radiation is still a matter of debate. A number of factors, such as non-target effects, adaptive responses and low-dose hypersensitivity, affect the long-term outcome of low-dose exposures. Cytogenetic bio-dosimetry provides a measure of the absorbed dose, taking into account the individual radiation sensitivity. The aim of the present study is to evaluate the value of the micronucleus (MN) test as a bio-dosimeter in hospital workers exposed to low doses of ionizing radiation. Blood samples were obtained from 30 subjects selected among workers exposed to X- and gamma-radiation, and 30 controls matched for sex, age and smoking from the same hospital. Micronucleus frequencies were analyzed by use of the cytokinesis-block method. The MN frequency was compared among the groups considering the confounding factors and the length of employment. No increase in the number of bi-nucleated cells with MN (BNMN), but a significant increase in the number of mono-nucleated cells with micronuclei (MOMN) was observed in exposed subjects compared with the controls. The relationship between MN frequency and accumulated dose (mSv) was evaluated. The length of employment did not affect the extent of MN frequency, but an increase of BNMN and MOMN cells was observed based on the accumulated radiation dose. Our study shows the sensitivity of the MN test in the detection of cytogenetic effects of cumulative exposure levels, suggesting the potential usefulness of this assay in providing a biological index in medical surveillance programs.

Biodosimetry and assessment of radiation dose

AIM

When investigating radiation accidents, it is very important to determine the exposition dose to the individuals. In the case of exposures over 1 Gy, clinicians may expect deterministic effects arising the following weeks and months, in these cases dose estimation will help physicians in the planning of therapy. Nevertheless, for doses below 1 Gy, biodosimetry data are important due to the risk of developing late stochastic effects. Finally, some accidental overexposures are lack of physical measurements and the only way of quantifying dose is by biological dosimetry.

BACKGROUND

The analysis of chromosomal aberrations by different techniques is the most developed method of quantifying dose to individuals exposed to ionising radiations.(1,2) Furthermore, the analysis of dicentric chromosomes observed in metaphases from peripheral lymphocytes is the routine technique used in case of acute exposures to assess radiation doses.

MATERIALS AND METHODS

Solid stain of chromosomes is used to determine dicentric yields for dose estimation. Fluorescence in situ hybridization (FISH) for translocations analysis is used when delayed sampling or suspected chronically irradiation dose assessment. Recommendations in technical considerations are based mainly in the IAEA Technical Report No. 405.(2.)

RESULTS

Experience in biological dosimetry at Gregorio Marañón General Hospital is described, including own calibration curves used for dose estimation, background studies and real cases of overexposition.

CONCLUSION

Dose assessment by biological dosimeters requires a large previous standardization work and a continuous update. Individual dose assessment involves high qualification professionals and its long time consuming, therefore requires specific Centres. For large mass casualties cooperation among specialized Institutions is needed.

The dose response of chromosome aberrations in human lymphocytes induced in vitro by very low-dose γ rays

This paper considers the dose-effect relationship for unstable chromosome aberration yields in human lymphocytes in very low-dose range. Data are presented for (60)Co γ-ray doses of 0, 10, 20, 40 and 1000 mGy. More than 5,000 metaphases were scored for each data point at the very low doses, and each cell was double-checked using a semi-automated metaphase finding/relocation system. Aberration yields of dicentrics plus centric rings followed an excellent linear dose response down to zero dose; the yields were significantly above the control frequency from 20 mGy.

Radiation-induced Chromosome Aberrations Analysed by Fluorescencein SituHybridization with a Triple Combination of Composite Whole Chromosome-specific DNA Probes

Fluorescence in situ hybridization (FISH) with a combination of three composite whole chromosome-specific DNA probes for human chromosomes 1, 4 and 12 was used to analyse in vitro radiation-induced dicentrics and symmetrical translocations in peripheral lymphocytes. Translocations could be rapidly and efficiently detected by FISH. Their frequencies were 1.8-fold higher than the frequencies for dicentrics at a given dose. The dose-response curves for translocations and dicentrics were linear quadratic with a significant higher quadratic component for translocations. The application of FISH for scoring stable translocations for biological dosimetry of radiation exposures is discussed.

Dose-rate effectiveness for unstable-type chromosome aberrations detected in mice after continuous irradiation with low-dose-rate gamma rays

Chronological changes in the chromosome aberration rates of splenocytes from specific-pathogen-free (SPF) mice after continuous and long-term exposure to low-dose-rate gamma rays were studied. Incidences of dicentrics plus centric rings (Dic+Rc), detected by conventional Giemsa staining, and dicentric chromosomes, detected by fluorescence in situ hybridization (Dic by FISH) using a centromere probe, showed an essentially linear increase up to a total accumulated dose of 8000 mGy after irradiation for about 400 days at a low dose rate of 20 mGy/day. For comparison, acute high-dose-rate and medium-dose-rate irradiation were performed. The values of the alpha coefficients in the linear regression lines for these unstable-type aberrations decreased as the dose rates were lowered from medium dose rates (200 and 400 mGy/day) to low dose rates (1 and 20 mGy/day). The dose and dose-rate effectiveness factor (DDREF), estimated by the ratio of calculated incidences using the best-fit regression lines at a high dose rate (890 mGy/min) and low dose rate (20 mGy/day), was 4.5 for Dic by FISH and 5.2 for Dic+Rc, respectively, at the same dose of 100 mGy, while different DDREFs were obtained for different accumulated doses. This is the first study to provide information regarding the effects of long-term exposure to low-dose-rate radiation on chromosomes.

Chromosome aberrations in peripheral blood lymphocytes of Croatian hospital staff occupationally exposed to low levels of ionising radiation

Medical staff is an occupational group exposed to different agents suspected to induce genetic damage. Among them ionising radiation is the most studied. Cytogenetic analysis of human chromosomes in peripheral lymphocytes allows direct detection of mutation in somatic cells. This study investigated the cytogenetic effects of low-level ionising x-radiation in 48-hour peripheral blood lymphocyte cultures sampled from 765 hospital staff occupationally exposed to several agents known or suspected to induce chromosome damage and compared them with 200 control subjects. The exposed subjects were divided in eight (8) groups according to their specialties and job titles. The exposed groups manifested an increase in all types of chromosome aberrations. Acentric fragments were the most frequent chromosome-type aberration. Dicentric chromosomes were statistically significant only in urologists/gynaecologists. Age and smoking significantly influenced the incidence of dicentrics in the exposed groups. The frequency of ring chromosomes was low in all exposed groups (range: 0-2), and none were found in the control group. These findings indicate the importance of periodic medical checkups of hospital staff occupationally exposed to low doses of ionising radiation. The purpose is to create an individual cytogenetic register, where changes could evidence individual risks.