Electron paramagnetic resonance in irradiated fingernails: variability of dose dependence and possibilities of initial dose assessment

Abstract

The results of electron paramagnetic resonance (EPR) measurements in irradiated fingernails are presented. In total, 83 samples of different fingernails were studied. Five different groups of samples were selected based on the collection time of fingernail samples, their level of mechanical stress, and the number and size of clippings: (1) recently (<24 h) cut, irradiated and measured with EPR without any treatment of samples, and with rigorous control of size and number of clippings (stressed-fresh, controlled); (2) recently (<24 h) cut, irradiated and measured with EPR after application of a special treatment (10 min of water soaking, 5 min of drying time) to reduce the mechanical stress caused by cutting the samples, and with rigorous control of size and number of clippings (unstressed-fresh, controlled); (3) previously (>24 h) cut, stored at room temperature, additionally cut into small pieces immediately prior to study, irradiated and measured with EPR without any treatment of samples, and with rigorous control of size and number of clippings (stressed-old, controlled); (4) previously (>24 h) cut, stored at room temperature, additionally cut into small pieces immediately prior to the study, irradiated and measured with EPR after application of a special treatment to reduce mechanical stress caused by cut, and with rigorous control of size and number of clippings (unstressed-old, controlled); and (5) recently (<24 h) cut, irradiated and measured with EPR after application of a special treatment to reduce the mechanical stress caused by cut, and without rigorous control of size and number of clippings (unstressed-fresh, uncontrolled). Except for the fifth selected group, variability of the dose dependence inside all groups was found to be not statistically significant, although the variability among the different groups was significant. Comparison of the mean dose dependences obtained for each group allowed selection of key factors responsible for radiation sensitivity (dose response per unit of mass and dose) and the shape of dose dependence in fingernails. The major factor responsible for radiation sensitivity of fingernails was identified as their water content, which can affect radiation sensitivity up to 35%. The major factor responsible for the shape of the radiation sensitivity was identified as the mechanical stress. At a significant level of mechanical stress, the shape of the dose dependence is linear in the studied dose range (<20 Gy), and in lesser-stressed samples it is of an exponential growth including saturation, which depends on the degree of mechanical stress. In view of the findings, recommendations are discussed and presented for the appropriate protocol for EPR dose measurements in fingernails.

EPR measurements of fingernails in Q-band

“…In order to reduce the MIS intensity, a procedure of short-time (5e10 min) soaking in water was suggested by Trompier et al (2007) and further developed in Reyes et al, 2008Reyes et al, , 2009 using a very small sample (2 mg). As it was discussed by Reyes et al (2008) soaking in water effectively eliminate MIS1, while MIS2 (stable mechanically-induced component) has a trend of slow increase with time after treatment.…”

“…1 shows the fading evolution of the MIS EPR spectra with time in freshly-cut unirradiated fingernail sample (1 piece, 2 mg) measured in Q-band. When comparing the MIS appearance in the X-band to that in the Q-band, no significant differences are observed in the spectra recorded immediately after the cuts of the nails (Chandra and Symons, 1987;Romanyukha et al, 2007b;Reyes et al, 2008Reyes et al, , 2009Wilcox et al, 2010;Black and Swarts, 2010). Although Q-band does not allow distinguishing more than the two main components of the MIS already observed in X-band: MIS1 (the doublet) and MIS2 (the singlet) (Reyes et al, 2009;Wilcox et al, 2010;Black and Swarts, 2010); the EPR spectrum measured at 181 min in Fig.…”

“…Significant progress in the development of electron paramagnetic resonance (EPR) dosimetry in fingernails has been achieved in recent years (see Reyes et al, 2008Reyes et al, , 2009Romanyukha et al, 2007bRomanyukha et al, , 2010Trompier et al, 2007Trompier et al, , 2009. Chemically, fingernails are mainly composed of alpha keratin, a protein made of three alpha helical peptide chains, twisted in a left-handed coil that is strengthened by disulfide bridges from adjacent cystein groups.…”

“…Variability of radiation sensitivity and RIS shape. According to Reyes et al (2009), the major factor responsible for variation of radiation sensitivity in fingernails is its water content, which can affect radiation sensitivity of fingernails up to 35%. The major factor responsible for the type (linear or exponential decay) of dose dependence of radiation-induced signal intensity was identified as the mechanical stress in fingernails at their cutting.…”

Comparison of Continuous Wave and Rapid Scan X-band Electron Paramagnetic Resonance of Irradiated Clipped Fingernails

“…There is renewed interest in quantitation of these electron paramagnetic resonance (EPR) signals because of their potential utility for measuring radiation dose, especially for medical triage in situations where there is a need to determine whether large numbers of people were exposed to medically significant doses of radiation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) . Fingernail dosimetry has been applied to three cases of accidental radiation exposure (14) .…”