Health Physics Society Meeting, Cleveland, OH, July 15-19, 2018
USTUR/COP student, Sara Dumit, presented the findings of her PhD research at the 63rd Annual Health Physics Society Meeting in Cleveland, Ohio. Additionally, Dan Strom presented a 2-dimensional representation of Leggett’s 2005 plutonium systemic model that emphasizes the recycling nature of the model.
New biokinetic model simultaneously fits Ca-DTPA affected and non-affected urine bioassay data after plutonium contamination
Sara Dumit (USTUR), Daniel J. Strom (USTUR), Stacey L. McComish (USTUR), Maia Avtandilashvil (USTUR)i, George Tabatadze (USTUR), Sergei Y. Tolmachev (USTUR)
Individuals with significant internal deposition of plutonium typically undergo medical treatment with chelating agents to enhance decorporation. The trisodium salt form of calcium diethylenetriaminepentaacetate (CaDTPA) is a commonly used decorporation drug that forms stable complexes with plutonium in vivo, enhancing its excretion in urine. Since plutonium biokinetics (absorption, distribution, retention, and excretion) are strongly altered by its complexation with the chelating agent, standard models cannot be used directly to estimate the radionuclide intake. Prior to this work, only empirical descriptions and ad hoc models and approaches were available to model data affected by chelation treatment. In this study, a new model that describes plutonium biokinetics during and following chelation therapy was developed, parameterized, and validated. A USTUR whole-body donor (Case 0212) was selected for this study. This individual was exposed to plutonium as a result of an occupational wound injury and underwent extensive treatment with Ca-DTPA. Urinary excretion measurements and post-mortem plutonium activities in the liver and the skeleton were used for model development and validation, respectively. The new model (linked with the Leggett et al. Plutonium Systemic Model, the ICRP 100 Human Alimentary Tract Model, and the NCRP 156 Wound Model) was implemented in SAAM II® software. The Coordinated Network for Radiation Dosimetry (CONRAD) approach to biokinetic modeling of decorporation therapy was applied by using a chelation constant to describe the kinetics of the in vivo chelation process. The new assumptions and parameters account for both the intravenously injected Ca-DTPA and the in vivo formed Pu-DTPA chelate. The new model structure was also tested with the ICRP 67 and the Luciani and Polig Plutonium Systemic Models. The fitting of urinary excretion and autopsy data using the new model was compared to the original CONRAD Model and its optimized version, resulting in both improved goodness-of-fit to the bioassay data by order of magnitude and more accurate predictions of post-mortem plutonium retention in major depository sites. [USTUR-0497-18A]
A simple visualization of the “Lekskam 2005 Model” of systemic plutonium biokinetics
Daniel J. Strom (USTUR)
In 2005, Leggett, Eckerman, Khokhryakov, Suslova, Krahenbuhl, and Miller (LEKSKaM) published a revision to the 1993 ICRP Publication 67 systemic biokinetic model for plutonium. Using data from plutonium workers in the former Soviet Union and Russian Federation, the model added a second blood compartment to mathematically deal with recycling. The resultant model is somewhat difficult to grasp conceptually, since one blood compartment is depicted inside another, necessitating pathways crossing compartment boundaries. Also, arrows in the model go in all directions. In an effort to develop a more intuitive representation of the model, an alternative view is presented. The visualization is a 2-dimensional surface projected in 3 dimensions onto the surface of a cylinder, emphasizing the recycling nature of the model. With uptake to Blood 1 shown at the top, excretion pathways shown at the bottom, and recycling going from left to right, all arrows go down or to the right. The Intake compartment is shown explicitly. The Skeleton, “Other” Kidney, Gonads, Soft Tissue 1 and 2, and Liver take Pu up from Blood 1 and gradually return it to Blood 2. The Intake Compartment, Renal Tubules, Urinary Bladder Contents, Small Intestine Contents, and Upper Large Intestine Contents are seen to be outside of the recycling part of the model. The unusual nature of ST0 (rapid turnover soft tissue) is clear. While there is no new science in this visualization, the flow of plutonium in the system is more easily comprehended. In principle, such visualizations can be made of all recycling models. [USTUR-0498-18A]