RENEB/EURADOS Field Exercise 2019: Robust Dose Estimation under outdoor Conditions based on the Dicentric Chromosome Assay

Depending on the exposure scenario, different biological and/or physical assays will be required to recover the exposure situation and to obtain reliable dose estimates to aid medical decision making. Inter-laboratory comparisons (ILCs) are a central tool to validate and improve the performance of methods and laboratories. In most cases such ILCs are performed under laboratory conditions where the influence of parameters contributing to uncertainties can be minimized. In a real-life scenario, the situation is much more complicated, and it is therefore crucial to validate methods and laboratories’ abilities to carry out these methods under more realistic conditions. In 2019, EURADOS (The European Radiation Dosimetry Group) Working Group 10 (Retrospective Dosimetry) and RENEB (Running the European Network of Biological and retrospective Physical dosimetry) organized a field exercise in Lund, Sweden, to validate different methods for biological and physical retrospective dosimetry in parallel by simulating real-life exposure scenarios. For the dicentric chromosome assay (DCA), 18 blood tubes were distributed across 8 thermos flasks filled with heated water and positioned at the hips and shoulders of anthropomorphic phantoms in different geometries. Two irradiations were performed with a 1.36 TBq ¹⁹²Ir-source, each with two phantoms, to simulate close, distant, lateral or partially shielded exposures. For each of the blood tubes DCA dose estimates were provided by at least one laboratory and for tubes from four thermos flasks by 17 participating RENEB laboratories. In addition, blood from the different thermos flasks on each phantom was mixed to simulate heterogeneous exposures. Three radio-photoluminescence (RPL) glass dosimeters (GD) were placed at each tube to assess reference doses and the inter- and intra-tube variability. The results from the DCA were homogeneous between participants and matched well with RPL GD reference doses (≥95% of estimates within ±0.5 Gy of the reference). For samples close to the source, exposed to doses >1 Gy, systematic underestimation could be corrected by accounting for exposure time. Heterogeneity within and between tubes was detected for RPL GD reference doses as well as for doses estimates from the DCA. The sample simulating a heterogeneous exposure with two different doses was detected by ∼50% of the participants. The participants were able to successfully estimate the doses and to provide important information on the exposure scenarios under conditions closely resembling a real-life situation. The reliability of the results emphasizes the value of the DCA for retrospective dosimetry under field conditions.