Triage of populations potentially exposed to clinically significant doses of ionizing radiation using in vivo EPR measurements of teeth

Full text: Purpose: Under the sponsorship of NIH, DTRA, and DARPA a multidisciplinary, multi-institutional team is developing a field deployable device capable of carrying out triage under field conditions for large numbers of exposed individuals. Method: The approach involves the development of techniques to obtain sufficiently accurate measurements of radiation-induced EPR signals in vivo from intact teeth in situ using a 1200 MHz EPR spectrometer developed specifically for making measurements in human subjects. The resonator utilizes a coupled loop that is placed on the tooth or teeth to be measured. The bridge and associated electronics detect and record the EPR signal, usually utilizing about 90 three second scans to obtain a sufficient signal/noise ratio. Post-acquisition software using the known characteristics of the radiation-induced EPR signal and the native background signal provides the estimate of the exposure dose. The technique is being developed, evaluated, and calibrated in vitro, and in vivo using normal subjects in which teeth which have been irradiated to specified doses, are placed at suitable vacancies in the dentition, and measurements made in vivo. Measurements for the same purposes also are made in patients who have received significant doses of radiation to their teeth in the course of radiation therapy. Additional measurements are being made in patients undergoing radiation therapy at the U. of Rochester using a clone of the EPR instrument developed at Dartmouth. Several permanent magnet systems are being evaluated for potential use for field deployment. These include the capability of transporting a version of the currently being used magnet on the back of a pick-up truck, and several smaller magnets that would not require the use of a vehicle for transportability. The latter include magnets that would be placed intra orally as well as compact extra oral magnets. The latter include a flat magnet that would be placed on one side of the head and several variants of more traditional shaped magnets. Major Findings: Between the time of submission and the meeting there will be a very intense period of research supported by a contract from DARPA and the continuing research supported by NIH, so the findings summarized here are expected to advance significantly in the interval. The technique already appears to have the capability of making the desired differentiation of the doses required for triage, although at the present time achievement of this resolution requires more time (about 15 minutes) than is desired for purposes of triage in the field for large numbers of individuals. The current technology uses loop tips that fit on the surface of molars, premolars, or canines. An intense effort at making the measurements in incisors is underway, because these teeth provide a more uniform surface among individuals and some advantages for rapid and accurate placement of the resonators by non-expert operators. Conclusions: In vivo EPR dosimetry using the radiation-induced free radicals in teeth appears to have considerable promise for triage of large numbers of individuals after an incident. It has the potential to provide immediate results without the need to gather samples and process them. (author)