MS Thesis Presentation by Ryan A. Lorio
Wednesday, August 10, 2005

(Dr. Nolan E. Hertel, Chair)

"Feasibility of Determining Radioactivity in Lungs Using a Thyroid Uptake Counter"

Abstract

In the event of a radiological attack on a civilian population, there will be a need to screen a large number of people for contamination in a timely and effective manner. With the increasing presence of nuclear medicine departments in local hospitals, a variety of radiation detection and imaging systems will exist that could be used to evaluate incoming patients. Utilizing the Monte Carlo N-Particle (MCNP5) radiation transport code developed by Los Alamos National Laboratory, the feasibility of using a thyroid uptake counter for detecting lung contamination has been investigated.

A variety of models were first created to validate the detector setup and code simulations against measured data obtained in a preliminary study. Measurements were previously made with discrete, encapsulated sources of 60 Co, 137 Cs, 192 Ir and 241 Am in an acrylic slab phantom as well as in air, with the source and detector system placed various distances apart. An additional setup was used to measure the count rates from a 131 I source uniformly distributed in a water-filled phantom.

The MCNP simulations provided the confidence required to do other calculations with the code and test geometries beyond those that were evaluated. Multiple anthropomorphic phantoms of various age, sex, and body mass were modeled to simulate variations in radioactive material distributions in the lungs as well as the change in detection efficiency due to varying thicknesses of intervening tissue. The minimal detectable activity of the thyroid probe and the corresponding dose to the human phantom were calculated for each setup. Collimated and uncollimated detector geometries were also analyzed to fully examine the detector's capabilities.