EPR dosimetry in nail samples irradiated in vivo during total body irradiation procedures

Abstract

Electron paramagnetic resonance (EPR) measurements of human's nails is a newly proposed method of retrospective biodosimetry based on quantitative ex vivo determination of EPR signals originating from free radicals induced in nails by ionizing radiation. In the presented study the nails were irradiated in vivo under controlled exposure conditions during total body irradiation (TBI) procedures with doses in nails about 15 Gy delivered through 3 days in 2 fractions per day. The authors applied two methods of reconstruction of the doses: one based on individualized calibration of the radiation-induced EPR signal (RIS) and the second one based on determination of the dose of maximum response (DMR) of so-called RIS5 EPR signal. The first method yielded doses from −3.5 Gy to 22.1 Gy for seven TBI patients. In all but one patient the reconstructed doses were considerably lower than the actual doses calculated by treatment plan, probably due to decay of the dosimetric EPR signal caused by contact of the nails with water during the patients' personal hygiene activities. The second method, based on the RIS5 signal, did not allow for reconstruction of the TBI doses mostly due to lack of the dose saturation features characteristic to RIS5. Further studies on the RIS5 method suggested, that its applicability can be related to the samples' geometry, i.e. the ratio of the total length (l) of cut edges to the mass (m) of the nail clippings: the dose saturation effect, characteristic for RIS5 radicals, was not observed for samples of relatively high l/m ratio. In addition, the study showed only limited resistance of the RIS5 radicals to water – water treatments longer than 10 min resulted in a decrease in the RIS intensity up to complete decay of the RIS for 60 min exposures of the irradiated clippings to water. Therefore it is concluded, that both methods are of limited reliability – only the method of direct calibration can provide, under conditions of minimized contact of nails with water before and after cutting, an indication of the radiation exposure in the examined dose range.