Validation of Monte Carlo Simulation of a Thyroid Uptake System Using Various Sources and a Slab Phantom

In the event of a terrorist act involving a radiological agent, internal contamination due to inhalation is a potential health threat. When a large population is potentially impacted, there is need for methodology to serve as an initial screening or triage tool to rapidly identify individuals with significant amounts of internal contamination and to assist in prioritizing collection of large numbers of bioassay samples needed in such an incident. Common handheld radiation detectors and medical devices are tools that can effectively and rapidly screen a large number of people for internal contamination due to gamma-emitting isotopes. This work investigated the use of a common medical device, a thyroid uptake system or thyroid probe, in screening for internal contamination in individuals. The response of a thyroid uptake system in such a situation can be estimated by using a validated Monte Carlo model of the thyroid uptake system and various human phantoms. A computational model of the thyroid uptake system was built using the Los Alamos Particle Transport Code, MCNP Version 5. The validation of this computational model was demonstrated by comparisons to a series of benchmark measurements using the actual device and six isotopes with a range of gamma-ray emission energies.