[en] 'Full text:' It is widely accepted that the dicentric chromosome assay (DCA) is currently the most sensitive and radiation-specific assay for measuring biological damage due to exposure to ionizing radiation. However, the utility of this assay following radiological or nuclear accidents is limited due to the time- and expertise-intensive nature of the microscopic scoring. As a strategy to increase throughput for this assay, a new scoring technique (termed DCA QuickScan) has been validated as an alternative rapid scoring approach. Unlike conventional DCA scoring, the individual centromeres are not counted when scoring using DCA QuickScan criteria, rather the metaphase spread is quickly examined (< 10 seconds) to confirm that it appears to be complete. If no damage is obvious during that examination, then the spread is scored as normal. If damage is observed (i.e. fragments, visible rings and/or dicentrics), the scorer carefully enumerates the damage. Each dicentric must be accompanied by an acentric fragment to reduce the chance of mistaking overlapping chromatids with true dicentrics. Evaluating spread morphology is a useful parameter for QuickScan scoring, where round or oval spreads are most reliably found to contain a complete chromosome compliment. As well, the use of an automated slide-maker has proven useful for providing spreads of consistent quality for use in QuickScan scoring. In a previous study, triage-quality conventional DCA and DCA QuickScan analyses were compared based upon scoring a minimum of 50 metaphase cells or 30 dicentrics by 9-15 scorers across 4 laboratories. Results from this pilot study indicated that QuickScan scoring was as accurate, and much faster than, conventional DCA analysis (a 6-fold decrease in scoring time was realized using DCA QuickScan). As a follow-up study, and as validation of this scoring strategy, these scoring methods have been compared by generating full dose response curves with 1000 metaphases or 200 dicentrics scored for each dose point. Blood samples were exposed to 0-4 Gy of gamma radiation, cultured by standard methods and scored using either conventional DCA or DCA QuickScan criteria. The time required for construction of the dose response curves, and the sensitivity of DCA QuickScan scoring in comparison to conventional DCA scoring, will be reported. (author)

[en] Enhanced cellular DNA repair efficiency and suppression of genomic instability have been proposed as mechanisms underlying the reduction of spontaneous and radiation-induced carcinogenesis in laboratory mice following low-dose radiation exposures. Our previous studies revealed that low-dose irradiation does not generate radio-adaptation by lowering radiation-induced DNA double-strand breaks, as indicated by the number of micronuclei in mouse spleen lymphocytes. These results were extended here by measuring dose and time dependent cytogenetic damage and proliferation changes in bone marrow erythrocyte populations of C57BL/6 and BALB/c mice. In C57BL/6 mice, the induction of micro-nucleated polychromatic erythrocytes (MN-PCE) was observed at doses of 100 mGy and greater, and suppression of erythroblast maturation occurred at doses of 500 mGy and higher. A linear dose response relationship for bone marrow MN-PCE frequencies 24 to 28 hours post-irradiation in C57BL/6 mice was established for doses between 100 mGy and 1 Gy, with departure from linearity at doses ≥ 1Gy. BALB/c mice exhibited increased MN-PCE frequencies following a 20 mGy radiation exposure but did not exhibit radio-sensitivity for MN-PCE frequencies following 2 Gy exposure. Radio-adaptation of bone marrow erythrocytes was not observed in either strain of mice exposed to low-dose priming irradiation (20, 100 mGy or 20 mGy x 4) administered at various times prior to acute 2 Gy irradiation, confirming the lack of radio-adaptive response for induction of cytogenetic damage or suppression or erythrocyte proliferation/maturation in bone marrow of these mouse strains. (author)

[en] The dicentric chromosome assay (DCA) is the 'gold'-standard assay for accurately estimating unknown radiological doses to individuals following radiological or nuclear accidents. However in a mass casualty scenario, the conventional DCA is not well suited for providing timely dose estimates due to the time- and expertise-intensive nature of this assay. In Canada, two approaches are being developed in an attempt to increase triage-quality biological dosimetry in a mass casualty scenario. These are: 1) increasing the number of trained personnel capable of conducting the DCA and, 2) evaluating alternative biodosimetry approaches or DCA variations, such as decreasing the number of metaphase cells scored. In a recent exercise, a new scoring technique (termed DCA QuickScan) was evaluated as an alternative rapid scoring approach. Conventional DCA and DCA QuickScan analysis was based upon scoring a minimum of 50 metaphase cells or 30 dicentrics by 9-15 scorers across 4 laboratories. Dose estimates for the conventional DCA were found to be within 0.5 Gy of the actual dose for 83% of the unknown samples, while DCA QuickScan dose estimates were within 0.5 Gy for 80% of the samples. Of the dose estimates falling 0.5 Gy or more outside the actual dose, the majority were dose over-estimates. It was concluded that the DCA QuickScan approach can provide critical dose information at a much faster rate than the conventional DCA without sacrificing accuracy. Future studies will further evaluate the accuracy of the DCA QuickScan method. (author)

[en] Currently, the dicentric chromosome assay (DCA) is used to estimate radiation doses to individuals following accidental radiological and nuclear overexposures when traditional dosimetry methods are not available. While being an exceptionally sensitive method for estimating doses by radiation, conventional DCA is time-intensive and requires highly trained expertise for analysis. For this reason, in a mass casualty situation, triage-quality conventional DCA struggles to provide dose estimations in a timely manner for triage purposes. In Canada, a new scoring technique, termed DCA QuickScan, has been devised to increase the throughput of this assay. DCA QuickScan uses traditional DCA sample preparation methods while adapting a rapid scoring approach. In this study, both conventional and QuickScan methods of scoring the DCA assay were compared for accuracy and sensitivity. Dose response curves were completed on four different donors based on the analysis of 1,000 metaphases or 200 events at eight to nine dose points by eight different scorers across two laboratories. Statistical analysis was performed on the data to compare the two methods within and across the laboratories and to test their respective sensitivities for dose estimation. This study demonstrated that QuickScan is statistically similar to conventional DCA analysis and is capable of producing dose estimates as low as 0.1 Gy but up to six times faster. Therefore, DCA QuickScan analysis can be used as a sensitive and accurate method for scoring samples for radiological biodosimetry in mass casualty situations or where faster dose assessment is required. (author)