Automated Dicentric Aberration Scoring for Triage Dose Assessment: 60Co Gamma Ray Dose-response at Different Dose Rates

Baseline micronucleus frequencies and 60Co cytokinesis-block micronucleus assay dose-response curve for biodosimetry in Vietnam

This study aims to establish baseline micronucleus (MN) frequencies from various populations of residents in Vietnam and develop a 60Co dose-response curve for the cytokinesis-block micronucleus (CBMN) assay. Blood samples were exposed in vitro to a 60Co source at a dose rate of 275 mGy per min in a range of 0.1 to 4.0 Gy. MN background frequencies were 4.5 ± 3.2, 7.3 ± 4.6, 7.0 ± 3.8 and 13.1 ± 6.7 in 1000 binucleated (BN) cells for 96 healthy donors, 22 male radiation workers and 12 breast cancer patients, respectively. Blood samples from three healthy donors were used to generate the MN dose-response curve: y = C + (0.0496 ± 0.0069)D + (0.0143 ± 0.0026)D2. This curve was verified through an inter-laboratory comparison (RENEB ILC 2021). Our findings highlight the significance of the CBMN assay as an additional essential tool for biodosimetry in Vietnam.

Development of high-throughput systems for biodosimetry

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

Metaphase Cells Enrichment for Efficient Use in the Dicentric Chromosome Assay

The dicentric chromosome assay (DCA), is considered the 'gold standard' for radiation biodosimetry. Yet, DCA, as currently implemented, may be impractical for emergency response applications, especially when time is of the essence, owing to its labor-intensive and time-consuming nature. The growth of a primary lymphocyte culture for 48 h in vitro is required for DCA, and manual scoring of dicentric chromosomes (DCs) requires an additional 24-48 h, resulting in an overall processing time of 72-96 h for dose estimation. In order to improve this timing. we introduce a protocol that will detect the metaphase cells in a population of cells, and then will harvest only those metaphase cells. Our metaphase enrichment approach is based on fixed human lymphocytes incubated with monoclonal, anti-phosphorylated H3 histone (ser 10). Antibodies against this histone have been shown to be specific for mitotic cells. Colcemid is used to arrest the mitotic cells in metaphase. Following that, a flow-cytometric sorting apparatus isolates the mitotic fraction from a large population of cells, in a few minutes. These mitotic cells are then spread onto a slide and treated with our C-Banding procedure [Gonen et al. 2022], to visualize the centromeres with DAPI. This reduces the chemical processing time to ~2 h. This reduces the time required for the DCA and makes it practical for a much wider set of applications, such as emergency response following exposure of a large population to ionizing radiation.

Application of a semi-automated dicentric scoring system in triage and monitoring occupational radiation exposure

The dicentric chromosome assay (DCA) is considered the gold standard for radiation biodosimetry, but it is limited by its long dicentric scoring time and need for skilled scorers. The automation of scoring dicentrics has been considered a strategy to overcome the constraints of DCA. However, the studies on automated scoring methods are limited compared to those on conventional manual DCA. Our study aims to assess the performance of a semi-automated scoring method for DCA using ex vivo and in vivo irradiated samples. Dose estimations of 39 blind samples irradiated ex vivo and 35 industrial radiographers occupationally exposed in vivo were estimated using the manual and semi-automated scoring methods and subsequently compared. The semi-automated scoring method, which removed the false positives of automated scoring using the dicentric chromosome (DC) scoring algorithm, had an accuracy of 94.9% in the ex vivo irradiated samples. It also had more than 90% accuracy, sensitivity, and specificity to distinguish binary dose categories reflecting clinical, diagnostic, and epidemiological significance. These data were comparable to those of manual DCA. Moreover, Cohen's kappa statistic and McNemar's test showed a substantial agreement between the two methods for categorizing in vivo samples into never and ever radiation exposure. There was also a significant correlation between the two methods. Despite of comparable results with two methods, lower sensitivity of semi-automated scoring method could be limited to assess various radiation exposures. Taken together, our findings show the semi-automated scoring method can provide accurate dose estimation rapidly, and can be useful as an alternative to manual DCA for biodosimetry in large-scale accidents or cases to monitor radiation exposure of radiation workers.

Comparison and Evaluation of Different Radiotherapy Techniques Using Biodosimetry Based on Cytogenetics

Simple Summary

Cell killing and tumor response in cancer patients depends not only on the absorbed radiation dose but also on the dose rate and delivery time. In this study, a biodosimetry assay based on the frequency of dicentrics chromosomes scored in peripheral blood lymphocytes from prostate cancer patients and PC3 human prostate cancer cell line was used to investigate the radiobiological impact of the relative prolonged dose delivery time and/or decreased dose rate met in advanced modulated radiotherapy techniques (VMAT and IMRT) compared to conventional non-modulated (3D-CRT) in prostate patient plan irradiations. The results showed a small but statistically significant decrease in the number of dicentrics following radiation with the modulated techniques, suggesting a corresponding decrease on the radiation dose efficiency. The biodosimetry assay could be used as an alternative to the laborious conventional clonogenic assay, while both lymphocytes and cancer cell line could effectively be used for estimation of the biological absorbed dose.

Abstract

While rapid technological advances in radiotherapy techniques have led to a more precise delivery of radiation dose and to a decreased risk of side effects, there is still a need to evaluate the efficacy of the new techniques estimating the biological dose and to investigate the radiobiological impact of the protracted radiotherapy treatment duration. The aim of this study is to compare, at a cytogenetic level, advanced radiotherapy techniques VMAT and IMRT with the conventional 3D-CRT, using biological dosimetry. A dicentric biodosimetry assay based on the frequency of dicentrics chromosomes scored in peripheral blood lymphocytes from prostate cancer patients and PC3 human prostate cancer cell line was used. For each patient blood sample and each subpopulation of the cultured cell line, three different irradiations were performed using the 3D-CRT, IMRT, and VMAT technique. The absorbed dose was estimated with the biodosimetry method based on the induced dicentric chromosomes. The results showed a statistically significant underestimation of the biological absorbed dose of ~6% for the IMRT and VMAT compared to 3D-CRT irradiations for peripheral blood lymphocytes, whereas IMRT and VMAT results were comparable without a statistically significant difference, although slightly lower values were observed for VMAT compared to IMRT irradiation. Similar results were obtained using the PC3 cell line. The observed biological dose underestimation could be associated with the relative decreased dose rate and increase irradiation time met in modulated techniques compared to the conventional 3D-CRT irradiations.

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

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

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

INTRODUCTION

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

OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Celebrating 60 Years of Accomplishments of the Armed Forces Radiobiology Research Institute1

Chartered by the U.S. Congress in 1961, the Armed Forces Radiobiology Research Institute (AFRRI) is a Joint Department of Defense (DoD) entity with the mission of carrying out the Medical Radiological Defense Research Program in support of our military forces around the globe. In the last 60 years, the investigators at AFRRI have conducted exploratory and developmental research with broad application to the field of radiation sciences. As the only DoD facility dedicated to radiation research, AFRRI's Medical Radiobiology Advisory Team provides deployable medical and radiobiological subject matter expertise, advising commanders in the response to a U.S. nuclear weapon incident and other nuclear or radiological material incidents. AFRRI received the DoD Joint Meritorious Unit Award on February 17, 2004, for its exceptionally meritorious achievements from September 11, 2001 to June 20, 2003, in response to acts of terrorism and nuclear/radiological threats at home and abroad. In August 2009, the American Nuclear Society designated the institute a nuclear historic landmark as the U.S.'s primary source of medical nuclear and radiological research, preparedness and training. Since then, research has continued, and core areas of study include prevention, assessment and treatment of radiological injuries that may occur from exposure to a wide range of doses (low to high). AFRRI collaborates with other government entities, academic institutions, civilian laboratories and other countries to research the biological effects of ionizing radiation. Notable early research contributions were the establishment of dose limits for major acute radiation syndromes in primates, applicable to human exposures, followed by the subsequent evolution of radiobiology concepts, particularly the importance of immune collapse and combined injury. In this century, the program has been essential in the development and validation of prophylactic and therapeutic drugs, such as Amifostine, Neupogen®, Neulasta®, Nplate® and Leukine®, all of which are used to prevent and treat radiation injuries. Moreover, AFRRI has helped develop rapid, high-precision, biodosimetry tools ranging from novel assays to software decision support. New drug candidates and biological dose assessment technologies are currently being developed. Such efforts are supported by unique and unmatched radiation sources and generators that allow for comprehensive analyses across the various types and qualities of radiation. These include but are not limited to both 60Co facilities, a TRIGA® reactor providing variable mixed neutron and γ-ray fields, a clinical linear accelerator, and a small animal radiation research platform with low-energy photons. There are five major research areas at AFRRI that encompass the prevention, assessment and treatment of injuries resulting from the effects of ionizing radiation: 1. biodosimetry; 2. low-level and low-dose-rate radiation; 3. internal contamination and metal toxicity; 4. radiation combined injury; and 5. radiation medical countermeasures. These research areas are bolstered by an educational component to broadcast and increase awareness of the medical effects of ionizing radiation, in the mass-casualty scenario after a nuclear detonation or radiological accidents. This work provides a description of the military medical operations as well as the radiation facilities and capabilities present at AFRRI, followed by a review and discussion of each of the research areas.

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.