Realising the European network of biodosimetry: RENEB-status quo

Potentials of cytokinesis blocked micronucleus assay in radiation triage and biological dosimetry

The measurement of micronucleus (MN) in the cytokinesis-block arrested binucleated cells has been extensively used as a biomarker in many radiation biology applications in specific biodosimetry. Following radiation casualties, medical management of exposed individuals begins with triage and biological dosimetry. The cytokinesis blocked micronucleus (CBMN) assay is the alternate for the gold standard dicentric chromosome assay in radiation dose assessment. In recent years, the CBMN assay has become well-validated and emerged as a method of choice for evaluating occupational and accidental exposures scenario. It is feasible due to its cost-effective, simple, and rapid dose assessment rather than a conventional chromosome aberration assay. PubMed search tool was used with keywords of MN, biodosimetry, radiotherapy and restricted to human samples. Since Fenech and Morely developed the assay, it has undergone many technical and technological reforms as a biomarker of various applications. In this review, we have abridged recent developments of the CBMN assay in radiation triage and biodosimetry, focusing on (a) the influence of variables on dose estimation, (b) the importance of baseline frequency and reported dose-response coefficient values among different laboratories, (c) inter-laboratory comparison and (d) its limitations and means to overcome them.

Identifying radiation responsive exon-regions of genes often used for biodosimetry and acute radiation syndrome prediction

Gene expression (GE) analysis of FDXR, DDB2, WNT3 and POU2AF1 is a promising approach for identification of clinically relevant groups (unexposed, low- and high exposed) after radiological/nuclear events. However, results from international biodosimetry exercises have shown differences in dose estimates based on radiation-induced GE of the four genes. Also, differences in GE using next-generation-sequening (NGS) and validation with quantitative real-time polymerase chain reaction (qRT-PCR) was reported. These discrepancies could be caused by radiation-responsive differences among exons of the same gene. We performed GE analysis with qRT-PCR using TaqMan-assays covering all exon-regions of FDXR, DDB2, WNT3 and POU2AF1. Peripheral whole blood from three healthy donors was X-irradiated with 0, 0.5 and 4 Gy. After 24 and 48 h a dose-dependent up-regulation across almost all exon-regions for FDXR and DDB2 (4–42-fold) was found. A down-regulation for POU2AF1 (two- to threefold) and WNT3 (< sevenfold) at the 3’-end was found at 4 Gy irradiation only. Hence, this confirms our hypothesis for radiation-responsive exon-regions for WNT3 and POU2AF1, but not for FDXR and DDB2. Finally, we identified the most promising TaqMan-assays for FDXR (e.g. AR7DTG3, Hs00244586_m1), DDB2 (AR47X6H, Hs03044951_m1), WNT3 (Hs00902258_m1, Hs00902257_m1) and POU2AF1 (Hs01573370_g1, Hs01573371_m1) for biodosimetry purposes and acute radiation syndrome prediction, considering several criteria (detection limit, dose dependency, time persistency, inter-individual variability).

The Potential of Omics in Biological Dosimetry

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

RENEB Inter-Laboratory comparison 2017: limits and pitfalls of ILCs

PURPOSE

In case of a mass-casualty radiological event, there would be a need for networking to overcome surge limitations and to quickly obtain homogeneous results (reported aberration frequencies or estimated doses) among biodosimetry laboratories. These results must be consistent within such network. Inter-laboratory comparisons (ILCs) are widely accepted to achieve this homogeneity. At the European level, a great effort has been made to harmonize biological dosimetry laboratories, notably during the MULTIBIODOSE and RENEB projects. In order to continue the harmonization efforts, the RENEB consortium launched this intercomparison which is larger than the RENEB network, as it involves 38 laboratories from 21 countries. In this ILC all steps of the process were monitored, from blood shipment to dose estimation. This exercise also aimed to evaluate the statistical tools used to compare laboratory performance.

MATERIALS AND METHODS

Blood samples were irradiated at three different doses, 1.8, 0.4 and 0 Gy (samples A, C and B) with 4-MV X-rays at 0.5 Gy min-1, and sent to the participant laboratories. Each laboratory was requested to blindly analyze 500 cells per sample and to report the observed frequency of dicentric chromosomes per metaphase and the corresponding estimated dose.

RESULTS

This ILC demonstrates that blood samples can be successfully distributed among laboratories worldwide to perform biological dosimetry in case of a mass casualty event. Having achieved a substantial harmonization in multiple areas among the RENEB laboratories issues were identified with the available statistical tools, which are not capable to advantageously exploit the richness of results of a large ILCs. Even though Z- and U-tests are accepted methods for biodosimetry ILCs, setting the number of analyzed metaphases to 500 and establishing a tests' common threshold for all studied doses is inappropriate for evaluating laboratory performance. Another problem highlighted by this ILC is the issue of the dose-effect curve diversity. It clearly appears that, despite the initial advantage of including the scoring specificities of each laboratory, the lack of defined criteria for assessing the robustness of each laboratory's curve is a disadvantage for the 'one curve per laboratory' model.

CONCLUSIONS

Based on our study, it seems relevant to develop tools better adapted to the collection and processing of results produced by the participant laboratories. We are confident that, after an initial harmonization phase reached by the RENEB laboratories, a new step toward a better optimization of the laboratory networks in biological dosimetry and associated ILC is on the way.

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

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

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.

Micronucleus Assay: The State of Art, and Future Directions

During almost 40 years of use, the micronucleus assay (MN) has become one of the most popular methods to assess genotoxicity of different chemical and physical factors, including ionizing radiation-induced DNA damage. In this minireview, we focus on the position of MN among the other genotoxicity tests, its usefulness in different applications and visibility by international organizations, such as International Atomic Energy Agency, Organization for Economic Co-operation and Development and International Organization for Standardization. In addition, the mechanism of micronuclei formation is discussed. Finally, foreseen directions of the MN development are pointed, such as automation, buccal cells MN and chromothripsis phenomenon.

The use of a centrifuge-free RABiT-II system for high-throughput micronucleus analysis

The cytokinesis-block micronucleus (CBMN) assay is considered to be the most suitable biodosimetry method for automation. Previously, we automated this assay on a commercial robotic biotech high-throughput system (RABiT-II) adopting both a traditional and an accelerated micronucleus protocol, using centrifugation steps for both lymphocyte harvesting and washing, after whole blood culturing. Here we describe further development of our accelerated CBMN assay protocol for use on high-throughput/high content screening (HTS/HCS) robotic systems without a centrifuge. This opens the way for implementation of the CBMN assay on a wider range of commercial automated HTS/HCS systems and thus increases the potential capacity for dose estimates following a mass-casualty radiological event.

CAPABILITIES OF THE ARADOS-WG03 REGIONAL NETWORK FOR LARGE-SCALE RADIOLOGICAL AND NUCLEAR EMERGENCY SITUATIONS IN ASIA

In 2015, the Asian Radiation Dosimetry Group established a regional network of biological dosimetry laboratories known as the ARADOS-WG03 (Working Group 03; Biological Dosimetry). A survey was conducted in 2017 to evaluate the capabilities and capacities of the participating laboratories for emergency preparedness and responses in large-scale nuclear and/or radiological incidents. The results of this survey were identified and assessed. The data provide important information on the current state of emergency cytogenetic biological dosimetry capabilities in the Asian region.

Development of an automatable micro-PCC biodosimetry assay for rapid individualized risk assessment in large-scale radiological emergencies

In radiation accidents and large-scale radiological emergencies, a fast and reliable triage of individuals according to their degree of exposure is important for accident management and identification of those who need medical assistance. In this work, the applicability of cell-fusion-mediated premature chromosome condensation (PCC) in G₀-lymphocytes is examined for the development of a rapid, minimally invasive and automatable micro-PCC assay, which requires blood volumes of only 100 μl and can be performed in 96-well plates, towards risk assessments and categorization of individuals based on dose estimates. Chromosomal aberrations are visualized for dose-estimation analysis within two hours, without the need of blood culturing for two days, as required by conventional cytogenetics. The various steps of the standard-PCC procedure were adapted and, for the first time, lymphocytes in blood volumes of 100 μl were successfully fused with CHO-mitotics in 96-well plates of 2 ml/well. The plates are advantageous for high-throughput analysis since the various steps required are applied to all 96-wells simultaneously. Interestingly, the use of only 1.5 ml hypotonic and Carnoy's fixative per well offers high quality PCC-images, and the morphology of lymphocyte PCCs is identical to that obtained using the conventional PCC-assay, which requires much larger blood volumes and 15 ml tubes. For dose assessments, appropriate calibration curves were constructed and for PCC analysis specialized software (MetaSystems) was used. The micro-PCC assay can be combined with fluorescence in situ hybridization (FISH), using simultaneously centromeric/telomeric (C/T) peptide nucleic acid (PNA) probes. This allows dose assessments on the basis of accurate scoring of dicentric and centric ring chromosomes in G₀-lymphocyte PCCs, which is particularly helpful when further evaluation into treatment-level categories of exposed individuals is needed. The micro-PCC assay has significant advantages for early triage biodosimetry when compared to other cytogenetic biodosimetry assays. It is rapid, cost-effective, and could pave the way to its subsequent automation.

UNCERTAINTY ON RADIATION DOSES ESTIMATED BY BIOLOGICAL AND RETROSPECTIVE PHYSICAL METHODS

Biological and physical retrospective dosimetry are recognised as key techniques to provide individual estimates of dose following unplanned exposures to ionising radiation. Whilst there has been a relatively large amount of recent development in the biological and physical procedures, development of statistical analysis techniques has failed to keep pace. The aim of this paper is to review the current state of the art in uncertainty analysis techniques across the 'EURADOS Working Group 10-Retrospective dosimetry' members, to give concrete examples of implementation of the techniques recommended in the international standards, and to further promote the use of Monte Carlo techniques to support characterisation of uncertainties. It is concluded that sufficient techniques are available and in use by most laboratories for acute, whole body exposures to highly penetrating radiation, but further work will be required to ensure that statistical analysis is always wholly sufficient for the more complex exposure scenarios.

Ionizing radiation biomarkers in epidemiological studies - An update

Recent epidemiology studies highlighted the detrimental health effects of exposure to low dose and low dose rate ionizing radiation (IR): nuclear industry workers studies have shown increased leukaemia and solid tumour risks following cumulative doses of <100mSv and dose rates of <10mGy per year; paediatric patients studies have reported increased leukaemia and brain tumours risks after doses of 30-60mGy from computed tomography scans. Questions arise, however, about the impact of even lower doses and dose rates where classical epidemiological studies have limited power but where subsets within the large cohorts are expected to have an increased risk. Further progress requires integration of biomarkers or bioassays of individual exposure, effects and susceptibility to IR. The European DoReMi (Low Dose Research towards Multidisciplinary Integration) consortium previously reviewed biomarkers for potential use in IR epidemiological studies. Given the increased mechanistic understanding of responses to low dose radiation the current review provides an update covering technical advances and recent studies. A key issue identified is deciding which biomarkers to progress. A roadmap is provided for biomarker development from discovery to implementation and used to summarise the current status of proposed biomarkers for epidemiological studies. Most potential biomarkers remain at the discovery stage and for some there is sufficient evidence that further development is not warranted. One biomarker identified in the final stages of development and as a priority for further research is radiation specific mRNA transcript profiles.

A New Cytogenetic Biodosimetry Image Repository for the Dicentric Assay

The BioDoseNet was founded by the World Health Organization as a global network of biodosimetry laboratories for building biodosimetry laboratory capacities in countries. The newly established BioDoseNet image repository is a databank of ~25 000 electronically captured images of metaphases from the dicentric assay, which have been previously analysed by international experts. The detailed scoring results and dose estimations have, in most cases, already been published. The compilation of these images into one image repository provides a valuable tool for training and research purposes in biological dosimetry. No special software is needed to view and score the image galleries. For those new to the dicentric assay, the BioDoseNet Image Repository provides an introduction to and training for the dicentric assay. It is an excellent instrument for intra-laboratory training purposes or inter-comparisons between laboratories, as recommended by the International Organization for Standardisation standards. In the event of a radiation accident, the repository can also increase the surge capacity and reduce the turnaround time for dose estimations. Finally, it provides a mechanism for the discussion of scoring discrepancies in difficult cases.

An update of the WHO Biodosenet: Developments since its Inception

In 2007 the World Health Organization established an international network of biodosimetry laboratories, the BioDoseNet. The goal of this network was to support international cooperation and capacity building in the area of biodosimetry around the world, including harmonisation of protocols and techniques to enable them to provide mutual assistance during a mass casualty event. In order to assess the progress and success of this network, the results of the second survey conducted in 2015 that assessed the capabilities and capacities of the members of the network, were compared to the similar first survey conducted in 2009. The results of the survey offer a unique cross-section of the global status of biodosimetry capacity and demonstrate how the BioDoseNet has brought together laboratories from around the world and strengthened the international capacity for biodosimetry.

Biodosimetry for High-Dose Exposures Based on Dicentric Analysis in Lymphocytes Released from the G2-Block by Caffeine

High-dose assessments using the conventional dicentric assay are essentially restricted to doses up to 5 Gy and only to lymphocytes that succeed to proceed to first post-exposure mitosis. Since G2-checkpoint activation facilitates DNA damage recognition and arrest of damaged cells, caffeine is used to release G2-blocked lymphocytes overcoming the mitotic index and dicentric yield saturation problems, enabling thus dicentric analysis even at high-dose exposures. Using the fluorescence in situ hybridization technique with telomere and centromere peptide nucleic acid probes, the released lymphocytes, identified as metaphases with decondensed chromosomes following 1.5 h caffeine treatment, show increased yield of dicentrics compared to that obtained in lymphocytes that reach metaphase without G2-checkpoint abrogation by caffeine. Here, a 3-h caffeine/colcemid co-treatment before harvesting at 55 h post-exposure is used so that the dicentric analysis using Giemsa staining is based predominantly on lymphocytes released from the G2-block, increasing thus dicentric yield and enabling construction of a dose-response calibration curve with improved precision of high-dose estimates.

Dose assessment intercomparisons within the RENEB network using G0-lymphocyte prematurely condensed chromosomes (PCC assay)

PURPOSE

Dose assessment intercomparisons within the RENEB network were performed for triage biodosimetry analyzing G₀-lymphocyte PCC for harmonization, standardization and optimization of the PCC assay.

MATERIALS AND METHODS

Comparative analysis among different partners for dose assessment included shipment of PCC-slides and captured images to construct dose-response curves for up to 6 Gy γ-rays. Accident simulation exercises were performed to assess the suitability of the PCC assay by detecting speed of analysis and minimum number of cells required for categorization of potentially exposed individuals.

RESULTS

Calibration data based on Giemsa-stained fragments in excess of 46 PCC were obtained by different partners using galleries of PCC images for each dose-point. Mean values derived from all scores yielded a linear dose-response with approximately 4 excess-fragments/cell/Gy. To unify scoring criteria, exercises were carried out using coded PCC-slides and/or coded irradiated blood samples. Analysis of samples received 24 h post-exposure was successfully performed using Giemsa staining (1 excess-fragment/cell/Gy) or centromere/telomere FISH-staining for dicentrics.

CONCLUSIONS

Dose assessments by RENEB partners using appropriate calibration curves were mostly in good agreement. The PCC assay is quick and reliable for whole- or partial-body triage biodosimetry by scoring excess-fragments or dicentrics in G₀-lymphocytes. Particularly, analysis of Giemsa-stained excess PCC-fragments is simple, inexpensive and its automation could increase throughput and scoring objectivity of the PCC assay.

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.

In vitro RABiT measurement of dose rate effects on radiation induction of micronuclei in human peripheral blood lymphocytes

Developing new methods for radiation biodosimetry has been identified as a high-priority need in case of a radiological accident or nuclear terrorist attacks. A large-scale radiological incident would result in an immediate critical need to assess the radiation doses received by thousands of individuals. Casualties will be exposed to different doses and dose rates due to their geographical position and sheltering conditions, and dose rate is one of the principal factors that determine the biological consequences of a given absorbed dose. In these scenarios, high-throughput platforms are required to identify the biological dose in a large number of exposed individuals for clinical monitoring and medical treatment. The Rapid Automated Biodosimetry Tool (RABiT) is designed to be completely automated from the input of blood sample into the machine to the output of a dose estimate. The primary goal of this paper was to quantify the dose rate effects for RABiT-measured micronuclei in vitro in human lymphocytes. Blood samples from healthy volunteers were exposed in vitro to different doses of X-rays to acute and protracted doses over a period up to 24 h. The acute dose was delivered at ~1.03 Gy/min and the low dose rate exposure at ~0.31 Gy/min. The results showed that the yield of micronuclei decreases with decreasing dose rate starting at 2 Gy, whereas response was indistinguishable from that of acute exposure in the low dose region, up to 0.5 Gy. The results showed a linear-quadratic dose-response relationship for the occurrence of micronuclei for the acute exposure and a linear dose-response relationship for the low dose rate exposure.

Comparing seven mitogens with PHA-M for improved lymphocyte stimulation in dicentric chromosome analysis for biodosimetry

Dicentric chromosome analysis (DCA) is the gold standard for individual radiation dose estimation. Two limiting factors of DCA are the time-consuming lymphocyte stimulation and proliferation using the lectin PHA-M and the upper dose limit of individual dose assessment of ∼4 Gy. By measuring the mitotic index (MI), the authors investigated systematically whether the stimulation of lymphocytes can be improved after administration of alternative (and combined) mitogens. The authors compared the lymphocyte stimulation effectiveness of the traditionally used PHA-M (from Phaseolus vulgaris) with seven cited mitogens by determination of MIs: five lectins namely CNA (concanavalin A), PW (pokeweed), LMA (Maackia amurensis), LTV (T. vulgaris), PHA-L (P. vulgaris) as well as LPS (lipopolysaccharide, Escherichia coli) and SLO (streptolysine O, Streptococcus pyogenes) were applied. The conventional protocol using PHA-M for lymphocyte stimulation proved to be superior over lower/higher PHA-M concentrations as well as seven other mitogens administered either alone or combined with SLO or LPS.

EURADOS strategic research agenda: vision for dosimetry of ionising radiation

Since autumn 2012, the European Radiation Dosimetry Group (EURADOS) has been developing its Strategic Research Agenda (SRA), which is intended to contribute to the identification of future research needs in radiation dosimetry in Europe. The present article summarises-based on input from EURADOS Working Groups (WGs) and Voting Members-five visions in dosimetry and defines key issues in dosimetry research that are considered important for the next decades. The five visions include scientific developments required towards (a) updated fundamental dose concepts and quantities, (b) improved radiation risk estimates deduced from epidemiological cohorts, (c) efficient dose assessment for radiological emergencies, (d) integrated personalised dosimetry in medical applications and (e) improved radiation protection of workers and the public. The SRA of EURADOS will be used as a guideline for future activities of the EURADOS WGs. A detailed version of the SRA can be downloaded as a EURADOS report from the EURADOS website (www.eurados.org).

Triage biodosimetry using centromeric/telomeric PNA probes and Giemsa staining to score dicentrics or excess fragments in non-stimulated lymphocyte prematurely condensed chromosomes

The frequency of dicentric chromosomes in human peripheral blood lymphocytes at metaphase is considered as the "gold-standard" method for biological dosimetry and, presently, it is the most widely used for dose assessment. Yet, it needs lymphocyte stimulation and a 2-day culture, failing the requirement of rapid dose estimation, which is a high priority in radiation emergency medicine and triage biodosimetry. In the present work, we assess the applicability of cell fusion mediated premature chromosome condensation (PCC) methodology, which enables the analysis of radiation-induced chromosomal aberrations directly in non-stimulated G0-lymphocytes, without the 2-day culture delay. Despite its advantages, quantification of an exposure by means of the PCC-method is not currently widely used, mainly because Giemsa-staining of interphase G0-lymphocyte chromosomes facilitates the analysis of fragments and rings, but not of dicentrics. To overcome this shortcoming, the PCC-method is combined with fluorescence in situ hybridization (FISH), using simultaneously centromeric/telomeric peptide nucleic acid (PNA)-probes. This new approach enables an accurate analysis of dicentric and centric ring chromosomes, which are formed within 8h post irradiation and will, therefore, be present in the blood sample by the time it arrives for dose estimation. For triage biodosimetry, a dose response curve for up to 10Gy was constructed and compared to that obtained using conventional metaphase analysis with Giemsa or centromeric/telomeric PNA-probes in metaphase. Since FISH is labor intensive, a simple PCC-method scoring Giemsa-stained fragments in excess of 46 was also assessed as an even more rapid approach for triage biodosimetry. First, we studied the rejoining kinetics of fragments and constructed a dose-response curve for 24h repair time. Then, its applicability was assessed for four different doses and compared with the PCC-method using centromeric/telomeric PNA-probes, through the evaluation of speed of analysis and minimum number of cells required for dose estimation and categorization of exposed individuals.