EPR retrospective dosimetry with fingernails: report on first application cases.

For localized irradiation to hands, in case of sources accidentally handled, it is very difficult to estimate the dose distribution by calculation. Doses may reach several tens of grays, and the dose distribution is usually very heterogeneous. Until recently, doses in such situations could be estimated only by analysis of bone biopsies using Electron Paramagnetic Resonance (EPR) spectroscopy. This technique was used previously on surgical wastes or after amputation of a finger. In this case, the dose information was available in one or a few locations on the hand only, due to the limited number of biopsy fragments usually collected. The idea to measure free radicals (FRs) induced by radiation in nails to estimate a dose is not new, but up to now, no application cases were reported. As a matter of fact, the EPR analysis of nails is complex due to the presence of intrinsic signals and parasitic signals induced by the mechanical stress (when nails are collected), which overlaps the radio-induced components. In addition, the radio-induced FRs identified up to now are unstable and very sensitive to humidity. In these conditions, it was difficult to foresee any application for dosimetry with fingernails. Recently, stable radio-induced FRs in nails has been identified and an associated protocol for dose assessment developed. This protocol has been applied by the Institut de Radioprotection et de Sûreté Nucléaire on fingernail samples from victims of three different radiological accidents that occurred between 2008 and 2012 in different places.