Effects of Ultraviolet Rays on L-Band In Vivo EPR Dosimetry Using Tooth Enamel

L-band electron paramagnetic resonance (EPR) in vivo dosimetry has the potential advantage of being able to accurately and sensitively measure the absorbed dose of ionizing radiation by measurements of teeth in situ. The equipment is transportable to the site where a radiation incident occurred and can be operated without specialized facilities. It, therefore, is very suitable for medical triage of victims in a large-scale radiation incident to quickly determine whether the dose was large enough to require urgent care. The measurements are made on the outer surfaces of the two upper incisor teeth. However, some in vitro studies of extracted teeth using higher frequency EPR have suggested that exposure to ultraviolet rays (UV) from sunlight might confound estimates of the dose of ionizing radiation made with EPR. Because the outer surfaces of incisors are likely to be exposed to UV/sunlight, it, therefore, is essential to determine the potential quantitative impact of UV on L-band EPR dosimetry measurements based on incisors. We, therefore, investigated the quantitative effect of UV on the EPR signal from ionizing irradiation of human teeth using the L-band spectrometer developed for field dosimetry. The UV-generated EPR signal was very small relative to the signals resulting from doses of ionizing radiation that are used for triage. For example, using our estimates of the effects of UV, for a lifetime of 50 years of exposure of these teeth (assuming an average exposure to sunlight of two hours/day), the expected average lifetime effect of UV-induced signal would be equivalent to 0.33 Gy; in contrast, triage criteria for accidental exposure to ionizing irradiation generally start at 2.0 Gy.