Elsevier

Radiation Measurements

Volume 42, Issues 6–7, July–August 2007, Pages 1110-1113
Radiation Measurements

EPR dosimetry in chemically treated fingernails

https://doi.org/10.1016/j.radmeas.2007.05.026Get rights and content

Abstract

By using EPR measurements of radiation-induced radicals it is possible to utilize human fingernails to estimate radiation dose after-the-fact. One of the potentially limiting factors in this approach is the presence of artifacts due to mechanically induced EPR signals (MIS) caused by mechanical stress during the collection and preparation of the samples and the so-called background (non-radiation) signal (BKS). The MIS and BKS have spectral parameters (shape, g-factor and linewidth) that overlap with the radiation-induced signal (RIS) and therefore, if not taken into account properly, could result in a considerable overestimation of the dose. We have investigated the use of different treatments of fingernails with chemical reagents to reduce the MIS and BKS. The most promising chemical treatment (20 min with 0.1 M dithiothreitol aqueous solution) reduced the contribution of MIS and BKS to the total intensity of EPR signal of irradiated fingernails by a factor of 10. This makes it potentially feasible to measure doses as low as 1 Gy almost immediately after irradiation. However, the chemical treatment reduces the intensity of the RIS and modifies dose dependence. This can be compensated by use of an appropriate calibration curve for assessment of dose. On the basis of obtained results it appears feasible to develop a field-deployable protocol that could use EPR measurements of samples of fingernails to assist in the triage of individuals with potential exposure to clinically significant doses of radiation.

Introduction

Experience has demonstrated that despite all precautions, radiation accidents occur. According to the Radiation Emergency Assistance Center/Training Site Radiation Accident Registries, in the period of 1944–2004 there were 421 major radiation accidents worldwide. There also is a high possibility of a terrorist act or the use of a strategic nuclear weapon that could result in the radiation exposure of civilians and military personnel. Therefore, development of a non-invasive, rapid and reliable method for measuring radiation dose that is able to provide results immediately after the radiation event is highly desirable. The use of fingernails as an EPR radiation dosimeter has a number of potential advantages including high sensitivity (Symons et al., 1995; Trompier et al., 2007a, Trompier et al., 2007b estimated low dose limits as 1–2 Gy); sampling is much more facile compared to hematologically based biodosimetry sampling (does not require drawing blood); and the measurement can be made at the site of the incident (does not require transport of the sample to a different site, avoiding the considerable logistical problems of linking back the individual with the sample under disaster conditions). The radiation-induced EPR signal persists for many hours and is dose proportional. If needed, the signal can be preserved indefinitely by storage at low temperatures.

But there is a problem—it is known from Symons et al. (1995) and Chandra and Symons (1987) that cutting fingernails generates mechanically induced radicals (MIS). In 1995, Symons et al. presented evidence that the dominant MIS species is a sulfur centered radical. The MIS has spectral parameters (shape, g-factor and linewidth) quite similar to the radiation-induced signal (RIS). Calculations that do not take this into account obviously overestimate the absorbed dose, e.g. the MIS could give a dose offset up to 10 Gy.

There are several possible approaches to try to solve this problem: annealing of the sample to accelerate fading of the MIS: numerical deconvolution of the fingernail spectrum to determine the radiation response from the complex spectrum; chemical treatment of the cut fingernails to oxidize the radical further; or a chemical reduction of the mechanically induced radicals.

It was reported by Chandra and Symons in 1987 that treatment with sodium thioglycolate reduces the MIS in cut fingernails. However, in the later paper by Symons et al. (1995), the authors, without reporting the details on which their decision was based, stated that they discontinued the use of this treatment because it “significantly modified the radiation response in fingernails”. In the present communication we report the results of the use of seven different chemicals (acetone, hydroxylamine, D,L-dithiothreitol, urea, sodium thioglycolate and hydrogen peroxide) to reduce the MIS in fingernails. Special attention was paid to the dose dependence of EPR radiation response in fingernails treated with D,L-dithiothreitol, a commonly used chemically reducing agent for proteins and peptides, which we found to be the most effective chemical treatment.

Section snippets

Experimental

Fingernails were collected from four different donors and were used in these experiments. Sharp surgical scissors were used to cut the fingernails. The pieces of fingernails all were about 1–2 mm wide and about 7–10 mm long. The typical sample mass was 15 mg. All chemicals were obtained from Aldrich and were 99+% pure. The water used for the rinsing steps and for solutions was 18.2MΩ and was provided by Millipore (Billerica, MA). A 137Cs radiation source with a dose rate of 0.7 Gy/min was used for

Results and discussion

Fig. 1 shows typical results of the experiments using the various treatments on unirradiated samples from one donor. Similar results were obtained with repetitions from the same donor and from measurements with three other donors, but because the experimental conditions had some variation, at this time the additional data should be viewed as supportive but cannot contribute to a statement of statistical significance. The best result (minimum MIS) was with the treatment with 0.1 M dithiothreitol

Conclusions

The chemical treatment procedure (10–20 min with an aqueous solution of 0.1 M dithiothreitol) reduced the MIS and BKS to 0.3 Gy from 10 Gy. These results suggest that it should be feasible to measure radiation doses in fingernails to below 1 Gy almost immediately after irradiation. Further experiments with replications and extension to using fingernails in which the MIS is generated after the irradiation (this could be done by irradiating “aged” fingernail clippings whose original MIS has decayed).

Acknowledgments

This study was supported in part by NIH Grant U19 AI067733 and used the facilities of the EPR Center for the Study of Viable Systems (P41 EB002032).

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