Retention of Highly Insoluble Plutonium Studied using Bayesian Statistics

USTUR Research Associate, Maia Avtandilashvili, has employed advanced statistical techniques to study the long-term retention of high-fired PuO₂ in the lungs of two USTUR donors (Cases 0202 and 0407). Dr. Avtandilashvili found that the current ICRP models may significantly underestimate the dose from this material. This is because high-fired PuO₂ is very insoluble and therefore takes longer to clear from the lungs than other forms of plutonium. For this type of material, the largest dose from deposited plutonium is delivered to the respiratory tract. Doses to other organs were approximately 10 to 100 times lower.

This work was performed as Dr. Avtandilashvili’s doctoral dissertation, while studying under Dr. Richard Brey at Idaho State University. Dr. Avtandilashvili graduated in December 2011 and was hired by the USTUR in January of 2012. Her work has been published as two papers in the Journal of Health Physics and presented at numerous Health Physics Society meetings.

Papers:
Avtandilashvili M., Brey R., James A.C. Maximum Likelihood Analysis of Bioassay Data from Long-term Follow-up of Two Refractory PuO₂ Inhalation Cases. Health Phys. 2012, 103(1): 70-79. (abstract)

Avtandilashvili M., Brey R., Birchall A. Application of Bayesian Inference to the Bioassay Data from Long-term Follow-up of Two Refractory PuO₂ Inhalation Cases. Health Phys. 2013. 104(4): 394-404. (abstract)

Most Recent Presentation:
Avtandilashvili M., Brey R., James A.C. Maximum Likelihood Analysis of Bioassay Data from Long-term Follow-up of Two Refractory PuO₂ Inhalation Cases. Health Phys. 57^th Annual Meeting of the Health Physics Society. Sacramento, CA. July 22-26, 2012. (read more)

Testing a Proposed Biokinetic Model

Q&A: What is a Biokinetic Model?

Biokinetic models are mathematical representations of the movement of material within the human body. The Gregoratto et al. model (above) breaks the respiratory tract into 10 compartments. Each compartment represents a different physiological region of the lung. For example, BBseq refers to material that is sequestered in the airway walls of the bronchial region, and LNTH refers to the thoracic lymph nodes. The arrows indicate how quickly material is cleared from one compartment to another. For example, plutonium is cleared from BBseq to LNTH at a rate of 0.01 d-1.

The International Commission on Radiation Protection’s (ICRP) Human Respiratory Tract Model (HRTM)¹ describes the deposition and clearance of inhaled material in the lungs. Since its publication in 1994, the HRTM has demonstrated merit under a broad set of situations. However, based upon new experimental evidence and reevaluation of existing data, the ICRP will be publishing an updated respiratory tract model. The new model will be based upon the work of Gregoratto et al.² who proposed a modified particle transport model that significantly simplified clearance from the lungs.

Dr. Avtandilashvili tested the Gregoratto et al. model by applying Bayesian statistics to bioassay data from two USTUR Registrants. These data included urinalyses, lung count results, and postmortem analysis of plutonium contents when available. It was found that “the Gregoratto et al. particle transport model can be applied to represent the bioassay and autopsy data available for two USTUR donors who were exposed to PuO₂ aerosols. However, case-specific model parameters [clearance rates] are still needed for an adequate representation of the observed data.”³ In light of the forthcoming revisions to the ICRP HRTM, Dr. Avtandilashvili’s work is very timely.

References

1. International Commission on Radiological Protection. Human respiratory tract model for radiological protection. New York: Pergamon Press. ICRP Publication 66. Ann ICRP. 1994, 24(1-3).
2. Gregoratto D., Bailey M.R., Marsh J.W. Modelling particle retention in the alveolar-interstitial region of the human lungs. J Radiol Prot. 2010, 30(3): 491-512.
3. Avtandilashvili M., Brey R., Birchall A. Application of Bayesian Inference to the Bioassay Data from Long-term Follow-up of Two Refractory PuO₂ Inhalation Cases. Health Phys. 2013. 104(4): 394-404.