Retrospective radiation dosimetry study of human teeth, bone and finger nail using electron paramagnetic resonance

Electron paramagnetic resonance (EPR) dosimetry of tooth enamel in X-band has been established as a suitable method for individual dose reconstruction of doses 0.1 Gy and higher. The principal disadvantage of this method has been the necessity to have extracted teeth available to supply the necessary large (∼100 mg) samples for dose measurements. To overcome this limitation, we investigated the use of Q-band EPR (34 GHz) instead of the conventional X-band (9 GHz). Q-band EPR requires significantly smaller amounts of enamel for measurements than does X-band. The objective of this study was to demonstrate the feasibility of using Q-band EPR in small tooth enamel biopsies to provide accurate measurements of absorbed radiation doses. We also investigated the use of Q-band EPR dosimetry with human dentin and bone, and with finger nails. An enamel biopsy technique was developed in vitro to obtain 2--4 mg enamel chips that caused minimal disturbance to tooth structure, leaving defects that could be quickly and easily restored with modern light-cured dental composite restorative materials. Our results have shown that Q-band provides accurate measurements of radiation doses higher than 0.5 Gy in tooth enamel biopsy samples as small as 2 mg. The other important advantage of Q-band is full resolution of the radiation-induced EPR signal from the radiation-independent native background signal. Feasibility study of the use of Q-band measurements in small (< 10 mg) samples of bone and dentin also showed better spectral resolution than X-band and enhanced possibility for dose assessment. Also by using Q-band 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 line width) 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.