In vivo EPR dosimetry of accidental exposures to radiation: experimental results indicating the feasibility of practical use in human subjects

Low frequency electron paramagnetic resonance (EPR) provides the potential advantage of making accurate and sensitive measurements of absorbed radiati on dose in teeth in situ, i.e. without removing the teeth from the potentia l victim. The potential limiting factors for making such measurements are: (1) whether low frequency EPR is sufficiently sensitive to detect radiation -induced signal in human teeth; (2) whether sufficient sensitivity can be m aintained under in vivo conditions. In this manuscript, we summarize result s indicating that this approach is feasible. Using 1.2 GHz EPR spectroscopy , we found that the lower limit for these measurements in isolated human te eth is 0.2 Gy or lower. Measurements of radiation-induced EPR signals in th e teeth of living rats were achieved with sufficient sensitivity to indicat e that, when taking into consideration the larger mass of human teeth, simi lar measurements in human teeth in situ would provide sensitivity in the do se range for potential accidental exposures. We estimate that the current l ower limit for detecting radiation doses in human teeth in situ (in vivo) i s 0.5-1.0 Gy; this would be sufficient for determining if a person has been exposed to potentially life threatening doses of ionizing radiation. The l imiting factor for sensitivity appears to be background signals rather than signal/noise, and there are feasible means to overcome this problem and fu rther increase sensitivity. The additional instrumental developments requir ed to make an effective in vivo EPR dosimetric spectrometer for the measure ments in teeth in human subjects in situ, seem quite achievable. (C) 2000 E lsevier Science Ltd. All rights reserved.