Abstract
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.
Highlights
Exposure to ionizing radiations poses an increasing threat to public health, from accidents involving medical radiological equipment failure, nuclear reactors, lost radioactive sources, and terrorist events incriminating radiation dispersal devices, radiation exposure devices, and improvised nuclear devices (INDs) [1]
We have previously described the establishment of a cytogenetic biodosimetry laboratory in Saudi Arabia along with producing a preliminary calibration curve composed of four volunteers [20]
Number of cells in metaphase assessed; No dicentrics, total number of dicentrics found in the metaphases assessed; Y, yield of dicentrics, i.e., the number of dicentrics per metaphase; SE, standard error on yield (Y); DI, dispersion index
Summary
Exposure to ionizing radiations poses an increasing threat to public health, from accidents involving medical radiological equipment failure, nuclear reactors, lost radioactive sources, and terrorist events incriminating radiation dispersal devices, radiation exposure devices, and improvised nuclear devices (INDs) [1]. To provide diagnostic information to treating physicians, the effective medical management of suspected acute radiation overexposures includes recording dynamic medical data, performing appropriate radiation bioassays for dose estimation, and measuring radioactivity for dose reconstruction [4] These include observing and documenting radiation-induced prodromal signs and symptoms, obtaining initial blood sample for complete blood counts and white blood cell differentials, assessing physical dose directly from the accident scene and personal dosimeters if available, and sampling blood for radiation bioassays. This is important because in the cases of radiation accidents with estimated exposures greater than 1 Gy, treating physicians may expect a range of dose-dependent deterministic effects, including serious acute radiation syndromes (ARSs) arising in the following weeks and months [5]. In the cases of radiation exposures with doses of less than 1 Gy, dose estimation is informative because of the potential risk of developing late stochastic effects, such as cancer, which mainly require long-term follow-up of exposed individuals [7]
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