Health Physics Society Meeting, Sacramento, CA, July 22-26, 2012
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USTUR faculty were authors on three presentations at the 57th Annual Meeting of the Health Physics Society (HPS) in Sacramento, CA, July 22-26, 2012.
Maia Avtandilashvili’s platform presentation was based upon her PhD research. Dr. Avtandilashvili received her PhD degree from Idaho State University (ISU) in December 2011, and joined the USTUR faculty as a health physics research associate in January 2012.
Sergei Tolmachev presented the sabbatical research of Bastian Breustedt, who was unable to attend the HPS meeting. Dr. Breustedt, a scientist from the Karlsruhe Institute of Technology in Germany, conducted a six-month sabbatical at the USTUR in 2011.
Majid Khalaf’s poster presentation described progress that he has made toward completion of his PhD. Mr. Khalaf is a student at ISU.
Maximum likelihood analysis of bioassay data from long-term follow-up of two refractory PuO2 inhalation cases
M. Avtandilashvili (ISU/USTUR), R. Brey (ISU), A. C. James (USTUR)
The U.S. Transuranium and Uranium Registries’ tissue donors 0202 and 0407 are the two most highly exposed of the 18 registrants who were involved in the 1965 plutonium fire accident at a defense nuclear facility. Material released during the fire was well characterized as “high fired,” refractory plutonium dioxide with 0.32 micrometer mass median diameter. The extensive bioassay data from long-term follow-up of these two cases were used to evaluate the applicability of the Human Respiratory Tract Model presented by International Commission on Radiological Protection in Publication 66 and its revision proposed by Gregoratto et al. in order to account for the observed long-term retention of insoluble material in the lungs. The maximum likelihood method was used to calculate the point estimates of intake and tissue doses and to examine the effect of different lung clearance, blood absorption and systemic models on the goodness-of-fit and estimated dose values. With appropriate adjustments, Gregoratto et al. particle transport model coupled with the customized blood absorption parameters yielded a credible fit to the bioassay data for both cases and predicted the Case 0202 liver and skeletal activities measured post-mortem. PuO2 particles produced by the plutonium fire are extremely insoluble. About 1% of this material is absorbed from the respiratory tract relatively rapidly, at a rate of about 1 to 2 d-1 (half-time about 8 to 16 h). The remainder (99%) is absorbed extremely slowly, at a rate of about 5×10-6 d-1 (half-time about 400 y). When considering this situation, it appears that doses to other body organs are negligible in comparison to those to tissues of the respiratory tract. About 96% of the total committed weighted dose equivalent is contributed by the lungs. Doses absorbed by these workers’ lungs were high: 3.2 Gy to the alveolar-interstitial region and 6.5 Gy to the thoracic lymph nodes for Case 0202 (18 y post-intake); 3.2 Gy to the alveolar-interstitial region and 55.5 Gy to the thoracic lymph nodes for Case 0407 (43 y post-intake). This evaluation supports the Gregoratto et al. proposed revision to the ICRP 66 model when considering situations of extremely insoluble particles. [USTUR-0317-11A]
Biokinetic modeling of chelation therapy for 241Am – USTUR Case 0846
B. Breustedt (KIT), S. McCord (USTUR), S. Tolmachev (USTUR)
Chelation therapy is a method to avert doses after incorporation of actinides. The perturbation of the biological processes cannot be described by the existing biokinetic models. Currently no generic model to describe the perturbation by chelation therapy exists. USTUR Case 0846 was a whole body donor who accidentally inhaled ~67 kBq 241Am, which was first reported in 1967. After confirmation of the intake, he was extensively chelated over 380 wk. Overall 313.5 g DTPA were given in 342 i.v. injections; 57 of them were 0.5 g doses, and 285 were 1 g doses. Virtually all urine was collected during the therapy. The gentleman, who died more than 40 years after the intake, was a whole body donor to the U.S. Transuranium and Uranium Registries (USTUR). Data available at USTUR, including original dosimetry and medical reports, have been analyzed to generate a dataset suitable for thorough biokinetic modeling of the chelation therapy. Based on post-mortem radiochemical tissue analyses, the total skeleton and liver were estimated to contain 30 kBq and 290 Bq of 241Am, respectively. The dataset will be completed when the remaining tissues have also been radiochemically analyzed. These radiochemistry results will provide an insight on the effects of DTPA-chelation therapy and support the biokinetic modeling. The methods used to generate the dataset, and the first steps in the assessment of this case and the development of a biokinetic model of decorporation therapy will be presented. [USTUR-0324-12A]
A new leg voxel model in two different positions for simulation of the non-uniform distribution of 241Am in leg bones
M. Khalaf (ISU), R. Brey (ISU), S. Tolmachev (USTUR)
A high quality new leg voxel model in two different positions (straight and bent) has been developed for in-vivo measurement calibration purpose. This voxel phantom is a representation of a human leg that may provide a substantial enhancement in Monte Carlo modeling, because it more accurately models different geometrical leg positions and the non-uniform distribution of 241Am throughout the leg bones, instead of assuming a one-position geometry and a uniform distribution of radionuclides. This was accomplished by performing a radiochemical analysis on small sections of the leg bones from the USTUR case 0846. To construct the voxel model, high resolution (2 mm) Computed Tomography (CT) images of the United States Transuranium and Uranium Registries USTUR case 0846 leg were obtained in different positions. Thirty-six objects (universes) were segmented manually from the CT images using the 3D-Doctor software. Bones were divided into 30-small sections with an assigned weight exactly equal to the weight of bone sections obtained from radiochemical analysis of the USTUR case 0846 leg. The segmented images were then converted into a boundary file and the Human Monitoring Laboratory (HML) voxelizer was utilized to convert the boundary file into the leg voxel phantom. Excluding the surrounding air regions, the straight leg phantom consists of 592,023 voxels, while the bent leg consists of 337,567 voxels. The resulting leg voxel model is now ready for use as a MCNPX input file to simulate in-vivo measurement of bone seeking radionuclides. [USTUR-0335-12A]