Dicentric assay: inter-laboratory comparison in Indian laboratories for routine and triage applications

An Inter-Laboratory Comparison (ILC) study on Dicentric Chromosome Assay (DCA) was carried out between biodosimetry labs located in and around Kalpakkam, Tamilnadu, India for capacity building. Four sets of human peripheral blood samples exposed to ten different doses (0-5 Gy) of X-rays (3 Gy/min) were shared between the labs and calibration curves constructed. No significant difference was observed between labs regarding their Dicentrics (DC) data (except at 2 Gy, p<0.05) and calibration curve parameters (t-test with Bonferroni correction, p<0.008). Validation of calibration curves was done by blind test method where dose blinded samples exposed to X-ray (1 and 2 Gy, at 3 Gy/min dose rate) or gamma radiation (1.71 and 2.14 Gy, at 0.63 Gy/min dose rate; ⁶⁰Co) were used. Doses were estimated by labs independently and are not significantly different from actual doses (p<0.006, with Bonferroni correction). Usefulness and reliability of the DCA data for triage application was evaluated by scoring 20, 50 and 100 metaphases in the dose range of 0.5-3.0 Gy. Prediction accuracy based on error (%) and sensitivity (proportion of actual positives correctly identified) was determined and results were highly comparable between labs. From the results it was observed that scoring 20 metaphases is adequate to detect radiation exposure of 2 Gy and above where as 50 metaphases is sufficient to determine radiation exposures of 0.5 Gy. However, it is recommended that for confirmation of such low doses a minimum of 100 metaphases be scored. This ILC study also reveals the reliability of DCA as a routine and triage biodosimetry tool in the biodosimetry labs indicated above. This is also a first step in the formation of biodosimetry network in India which is essential especially when the country is aiming at capacity building in nuclear energy in the next two decades. (author)