Dosimetry based on EPR spectral analysis of fingernail clippings

Abstract

Exposure of fingernails and toenails to ionizing radiation creates radicals that are stable over a relatively long period (days to weeks) and characterized by an isotropic EPR signal at g = 2.003 (so-called radiation-induced signal, RIS). This signal in readily obtained fingernail parings has the potential to be used in screening a population for exposure to radiation and determining individual dose to guide medical treatment. However, the mechanical harvesting of fingernail parings also creates radicals, and their EPR signals (so-called mechanically-induced signals, MIS) overlap the g approximately 2.0 region, interfering with efforts to quantify the RIS and, therefore, the radiation dose. Careful analysis of the time evolution and power-dependence of the EPR spectra of freshly cut fingernail parings has now resolved the MIS into three major components, including one that is described for the first time. It dominates the MIS soon after cutting, but decays within the first hour and consists of a unique doublet that can be resolved from the RIS. The MIS obtained within the first few minutes after cutting is consistent among fingernail samples and provides an opportunity to achieve the two important dosimetry objectives. First, perturbation of the initial MIS by the presence of RIS in fingernails that have received a threshold dose of radiation leads to spectral signatures that can be used for rapid screening. Second, decomposition of the EPR spectra from irradiated fingernails into MIS and RIS components can be used to isolate and thus quantify the RIS for determining individual exposure dose.

Figure 1

Cut-away representation of the configuration of a whole fingernail sample in an EPR tube positioned in the EPR resonator cavity adjacent to an EPR standard.

Figure 2

EPR spectra (1 mW) of a fingernail sample that had not been irradiated (top) and a fingernail sample that had received 10 Gy radiation (bottom); in each case the spectra were taken at the indicated time after the sample was cut into five pieces; features at 3455 and 3545 G are two of the six hyperfine lines of the Mn⁺² in CaO EPR standard.

Figure 3

EPR spectra (1 mW) of the initial transient MIS of a fingernail sample at the indicated time after it was cut into five pieces; EPR spectra of the final (persistent) MIS and the EPR standard have been subtracted from each spectrum.

Figure 4

EPR spectra at the indicated microwave power of the final (persistent) MIS of a fingernail sample ≥2 hr after it was cut into five pieces; features at 3455 and 3545 G are two of the six hyperfine lines of the Mn⁺² in CaO EPR standard.

Figure 5

EPR spectra at the indicated microwave power of the g = 2.003 feature (top) and the broad features (bottom) of the final (persistent) MIS of a fingernail sample ≥2 hr after it was cut into five pieces; the g = 2.003 spectra were obtained by subtracting a normalized spectrum of the sample at high power, and the broad features were obtained by subtracting a normalized spectrum of the sample at low power; inserts indicate the signal intensity as a function of microwave power.

Figure 6

EPR spectrum (3 mW) of a fingernail sample 2 min after it was cut into five pieces (black), and EPR spectra of its three MIS components; MIS2 (red) was obtained by subtraction of a 3 mW spectrum from a 12 mW spectrum, and MIS1 (green) and MIS3 (lavender) were obtained by subtracting MIS2 from the fingernail EPR spectrum obtained 2 hr and 2 min after the cutting, respectively.

Figure 7

EPR spectra (1 mW) of a fingernail sample that had not been irradiated (top) and a fingernail sample that had received 10 Gy radiation (bottom) taken 2, 15 and 120 min after the sample was cut into five pieces; constant derivative features on both ends of each spectra are two of the six hyperfine lines of the Mn⁺² in CaO EPR standard.

Figure 8

Top: normalized EPR spectra (3 mW) of the initial transient MIS in fingernail samples from 11 volunteers obtained 2 min after the fingernails were cut into five pieces; Bottom: EPR spectrum of a 10 Gy irradiated fingernail sample obtained 2 min after it was cut into five pieces (black, MIS/RIS), a normalized average EPR spectrum obtained from non-irradiated fingernail samples 2 min after they were cut into five pieces (red, MIS), and the EPR spectrum (blue, RIS) resulting from subtraction of the MIS spectrum (red) from the MIS/RIS spectrum (black); EPR spectra of the broad MIS2 signal and the Mn⁺² standard have been subtracted from each spectrum.