Optimization of cytogenetic procedures for population triage in case of radiological emergency

Titre de la revue : Radiation Measurements Volume : 42 N° : 6-7 Pagination : 1143-1146 Date de publication : 01/07/2007

In case of accidental overexposure to ionizing radiation, the scoring of dicentrics in lymphocytes from blood is the current reference method to estimate the dose received. When only few individuals are accidentally overexposed, at least 500 cells are scored to have a good estimation of the dose. But such a practice is too time consuming when many people are exposed such as in a radiological emergency. In order to reduce the time required to estimate a dose, specific strategies have been developed in the laboratory. Population triage based on the adaptation of the dicentrics assay: In order to reduce the analysis time it is possible to have a dose estimation based on only 50 cells analysed in an hour with a 95% confidence limit of 1 Gy. Population triage based on the use of image analysis systems: The metaphase finder increases the speed of the scoring by a factor of 2. It is also possible to detect automatically the dicentrics. The system proposes to the operator some candidate dicentrics which are then verified manually. In this case, 50% of the dicentrics are correctly detected with a 95% confidence limit of 0.4 Gy. Establishment of a network: Biological dosimetry laboratories are small, hence their capacity can be overloaded by a large number of suspected overexposed individuals. That is why international and national networks should be established, they should perform periodically intecomparisons and population triage exercises. Population triage based on micronuclei assay: As micronuclei are easier to score than dicentrics, in an hour 500 binucleated cells can be scored resulting in a 95% confidence limit of about 0.5 Gy versus 1 Gy with the dicentric assay. However, the micronuclei technique is not efficient to estimate accurately the dose because it lacks specificity. Use ofγ -H2AX for population triage: This assay is based on the scoring of double-strand breaks. Whereas with the other technique a cell culture is required, here it is possible to estimate a dose 3 h after receiving the sample in the laboratory with a sensitivity below 0.5 Gy. But one major limitation is the decrease of the signal with time. Therefore, this assay can only be used in case of population triage starting within minutes post-exposure.