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A new modification of the prior human lung compartment plutonium model, Doses-2005, has been described. The modified model was named "Mayak Worker Dosimetry System-2008" (MWDS-2008). In contrast to earlier models developed for workers at the Mayak Production Association (Mayak PA), the new model more correctly describes plutonium biokinetics and metabolism in pulmonary lymph nodes. The MWDS-2008 also provides two sets of doses estimates: one based on bioassay data and the other based on autopsy data, where available. The algorithm of internal dose calculation from autopsy data will be described in a separate paper. Results of comparative analyses of Doses-2005 and MWDS-2008 are provided. Perspectives on the further development of plutonium dosimetry are discussed.

Plutonium-238 (238Pu) has a half-life of about 87.7 y and thus a higher specific activity than 239Pu. It is used in radioisotope thermoelectric generators and is a substantial source of plutonium alpha-radiation in spent nuclear fuels. Early animal studies demonstrated differences in the biokinetics of inhaled oxides of 238Pu and 239Pu with 238Pu having a substantially more rapid translocation from the lungs to the systemic organs, particularly the skeleton. This resulted in the predominant occurrence of skeletal cancers in animals exposed to 238Pu oxides but lung cancers in those with exposures to 239Pu oxides. The anatomical distribution of osteogenic sarcomas seen in animal studies was similar to that observed with 239Pu and also in plutonium workers but differed from naturally occurring tumors. The in vivo "solubility" of 238Pu has been associated with the relative amounts of 238Pu/239Pu in the particles and calcination temperatures during the preparation of the dioxides. There is experimental evidence of in vivo 238Pu particle fragmentation attributed to nuclear recoil during radioactive decay. The resulting conversion of microparticles to nanoparticles may alter their interactions with macrophages and transport across epithelial barriers. There are few documented cases of human exposures, but the biokinetics appeared to depend on the chemical and physical nature of the aerosols. Robust human biokinetic and dosimetric models have not been developed, due in part to the lack of data. With the acceleration of nuclear technologies and the greater demand for reprocessing and/or disposal of spent nuclear fuels, the potential for human exposure to 238Pu will likely increase in the future.

The Doses-2005 model is a combination of the International Commission on Radiological Protection (ICRP) models modified using data from the Mayak Production Association cohort. Surrogate doses from inhaled plutonium can be assigned to approximately 29% of the Mayak workers using their urine bioassay measurements and other history records. The purpose of this study was to quantify and qualify the uncertainties in the estimates for radiation doses calculated with the Doses-2005 model by using Monte Carlo methods and perturbation theory. The average uncertainty in the yearly dose estimates for most organs was approximately 100% regardless of the transportability classification. The relative source of the uncertainties comes from three main sources: 45% from the urine bioassay measurements, 29% from the Doses-2005 model parameters, and 26% from the reference masses for the organs. The most significant reduction in the overall dose uncertainties would result from improved methods in bioassay measurement with additional improvements generated through further model refinement. Additional uncertainties were determined for dose estimates resulting from changes in the transportability classification and the smoking toggle. A comparison was performed to determine the effect of using the model with data from either urine bioassay or autopsy data; no direct correlation could be established. Analysis of the model using autopsy data and incorporation of results from other research efforts that have utilized plutonium ICRP models could improve the Doses-2005 model and reduce the overall uncertainty in the dose estimates.

The purpose of this study was to develop a biokinetic model that uses urinary plutonium excretion rate data to estimate the plutonium accumulation in the human respiratory tract after occupational exposure. The model is based on autopsy and urinalysis data, specifically the plutonium distribution between the respiratory tract and the remainder of the body, taken from 543 former workers of a radiochemical facility at the Mayak Production Association (MPA) plant. The metabolism of plutonium was represented with a compartmental model, which considers individual exposure histories and the inherent solubility properties of industrial plutonium aerosols. The transport properties of plutonium-containing aerosols were estimated by experimentally defining their in vitro solubility. The in vitro solubilities were found by dialysis in a Ringer's solution. Analysis of the autopsy data indicated that a considerable fraction of the inhaled plutonium is systemically redistributed rapidly after inhalation. After the initial dynamic period, a three-compartment model describes the retention in the respiratory tract. One compartment describes the nuclide retained in the lungs, the second compartment describes a plutonium lung concentration that exponentially decreases with time, and the third compartment describes the concentration in the pulmonary lymph nodes. The model parameters were estimated by minimizing sum squared of the error between the tissue and bioassay data and the model results. The parameters reflect the inverse relationship between plutonium retention in lungs and the experimentally derived aerosol transportability. The model was validated by comparing the autopsy results with in vivo data for 347 cases. The validation indicates that the model parameters are unbiased. This model is being used to estimate individual levels of nuclide accumulation and to compute radiation doses based upon the urinary excretion rates.

One of the objectives of the Joint Coordinating Committee for Radiation Effects Research Project 2.4 is to document the methodology used to determine the radiation doses in workers from the Mayak Production Association who were exposed to plutonium. The doses have been employed in numerous dose response studies measuring both stochastic and deterministic effects. This article documents both the historical (pre-1999) and current ("Doses 1999") methods used by the FIB-1 scientists to determine the doses. Both methods are based on a three-chamber lung model developed by the FIB-1 scientists. This method was developed in partial isolation from the West and has unique characteristics from the more familiar ICRP biokinetic models. Some of these characteristics are the use of empirically based transportability classifications and the parameter modification for chelation-therapy-enhanced excretion data. An example dose calculation is provided and compared to the dose that would be obtained if the ICRP models were used. The comparison demonstrates that the models are not interchangeable and produce different results.

The United States Transuranium and Uranium Registries (USTUR) and the Dosimetry Registry of the Mayak Industrial Association (DRMIA) havebeen independently collecting tissues at autopsy of plutonium workers in their respective countries for nearly 30 y. The tissues are analyzed radiochemically and the analytical data are used to develop, modify, or refine biokinetic models that describe the depositions and translocations of plutonium and transplutonium elements in the human body. The purpose of this collaborative research project is to combine the unique information on humans, gathered by the two Registries, into a joint database and perform analyses of the data. A series of project tasks are directly concerned with dosimetry in Mayak workers and involve biokinetic modeling for actinide elements. Transportability coefficients derived from in-vitro solubility measurements of actinide-containing aerosols (as measured by the DRMIA) were related to specific workplaces within Mayak facilities. The transportability coefficients of inhaled aerosols significantly affected the translocation rates of plutonium from the respiratory tract to the systemic circulation. Parameters for a simplified lung model, used by Branch No. 1, Federal Research Center Institute of Biophysics (FIB-1) and the Mayak Production Association for dose assessment at long times after inhalation of plutonium-containing aerosols, were developed on the basis of joint USTUR and DRMIA data. This model has separate sets of deposition and transfer parameters for three aerosol transportability groups, allowing work histories of the workers to be considered in the dose-assessment process. FIB-1 biokinetic models were extended to include thedistributions of actinide elements in systemic organs of workers, and a relationship between the health of individual workers and plutonium distribution in tissues was determined. Workers who suffered from liver diseases generally had a smaller fraction of systemic plutoniumin [ABSTRACT FROM AUTHOR]