SUMMARY

This study investigated the use of a common medical device, a thyroid uptake system or thyroid probe, in assessing internal contamination in individuals. In the event of a terrorist act involving a radiological agent, there will be a need to effectively and rapidly screen a large number of people for internal contamination. Using the methodology outlined in this study, those needing further medical assistance can be identified and separated from uncontaminated or very lightly contaminated people. Additionally, this information could be stored in a registry to track population contamination. A series of measurements and models was used in this study to estimate the response of the thyroid probe to radioactive isotopes in various human phantoms. First, benchmark measurements were made using a polymethyl methacrylate (PMMA) slab phantom and a variety of gamma-ray emitting isotopes. The laboratory setup was recreated in a computational model using the Los Alamos Monte Carlo N-Particle Transport Code, MCNP5. The thyroid uptake collimator was also modeled using this code, and simulations were completed for each laboratory measurement. A comparison of these results validated the computational model of the thyroid uptake collimator. Six anthropomorphic phantoms of varying age and body type were then used in conjunction with the thyroid uptake collimator. These phantoms are based on the Medical Internal Radiation Dose (MIRD) phantoms, and were originally developed at Oak Ridge National Laboratory. Uniformly distributed sources were placed in all the affected organs according to biokinetic models generated by the Dose and Risk Calculation Software (DCAL). This study found that a collimated thyroid uptake probe could not be used to assess individuals contaminated with Am-241. The thyroid uptake probe is a viable tool for assessing internal contamination due to Cs-137, Co-60, I-131, and Ir-192, even at relatively high levels of background.