USTUR faculty members were authors on five abstracts that were presented at the 56th Annual Health Physics Society Meeting in West Palm Beach, FL, June 26 – 30, 2011:
USTUR’s Stacey McCord gave an oral presentation titled “Distribution of Terminal Lung and Liver Dose Rates in United States Transuranium and Uranium Registries Registrants.”
Dr. Gary Kramer of Health Canada, Ottawa, gave an oral presentation titled, “Comparison of two leg phantoms containing Am-241 in bone.”
Three Idaho State University students – George Tabatadze, Maia Avtandilashvili, and Majid Khalaf – gave poster presentations on their PhD research. USTUR’s Dr. Anthony James is on each of these students’ doctoral committees and he is an author on their poster presentations.
Distribution of Terminal Lung and Liver Dose Rates in United States Transuranium and Uranium Registries Registrants
S.L. McCord (USTUR), A.C. James (USTUR), S.Y. Tolmachev (USTUR)
Initiated in the 1960’s with the mission of acquiring and providing precise information about the effects of plutonium and other transuranic elements in man, the United States Transuranium Registries (USTUR) have followed up over 400 volunteer Registrants who worked at weapons sites and received measurable internal doses from actinide elements. Samples of body organs are donated by our deceased Registrants. The activity concentrations of 241Am, 238Pu, 239/240Pu, 241Pu, 234U, 235U, and/or 238U have been radiochemically measured in post-mortem lung specimens from 295 of our 332 donors. Actinide activities have also been measured in liver samples from 287 of our donors. The average alpha absorbed dose rates at the time of death – terminal dose rates (TDRs) – to the liver and lungs from actinides have been calculated from these activity concentrations. The lung TDRs overlap with those in beagle dogs from PNNL/ITRI’s lifespan inhalation studies and vary from a minimum of 2.4 x 10-6 mGy/y to a maximum of 242 mGy/y. The geometric mean of the lung TDRs is 5.0 x 10-2 mGy/y with a geometric standard deviation (GSD) of 29 mGy/y. Liver TDRs vary from 1.3 x 10-5 to 690 mGy/y. The geometric mean of the liver TDRs is 3.5 x 10-2 with a GSD of 12 mGy/y. No increase in the incidence of lung or liver cancer with increasing lung TDR or liver TDR, respectively, is apparent.
Comparison of Two Leg Phantoms Containing Am-241 in Bone
G.H. Kramer, B.M. Hauck, K. Capello, W. Rühm , D. Broggio, D. Franck, M.A. Lopez, T. Navarro, J.F. Navarro, S. Tolmachev
Three facilities (Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas , Helmholtz Zentrum München, and the Human Monitoring Laboratory) have used their in vivo counters to compare two leg phantoms. One was commercially produced with activity artificially added to the bone inserts. The other was manufactured from Am-241 contaminated bones resulting from an intake. The comparison of a commercially available leg phantom in which the activity has been artificially distributed with a leg phantom in which the activity has been deposited though normal metabolic processes shows a distinct difference in the activity distribution between the two phantoms. An error in the activity estimate can be quite large if the commercial leg phantom is used to estimate what is contained in the United States Transuranium and Uranium Registries (USTUR) leg phantom and, consequently, a real person. As the latter phantom was created as a result of a real contamination it is deemed to be the more representative of what would actually happen if a person were internally contaminated with Am-241. Thus it is concluded that, whenever available, a naturally contaminated phantom should be used rather than artificially contaminated ones. It is clear, however, that those naturally contaminated phantoms are very rare as they require body donations of contaminated individuals. To the best of the authors’ knowledge, USTUR is one of the very few places worldwide (if not the only one) where such naturally contaminated phantoms can be and have already been produced. This demonstrates the unique position USTUR has to support in vivo counting techniques developed for actinide measurements and help Internal Dosimetrists make the best possible dose estimate (and hence health risk).
Modeling Am-241 Distribution in Bones of the USTUR Case 0102 Human Leg Phantom
G. Tabatadze (ISU), R. Brey (ISU), A. James (USTUR)
Whole-body-counting gamma-spectrometry is one of the specialized techniques for monitoring internal exposure to various radionuclides. Calibration of these systems is based on the use of tissue equivalent plastic phantoms which contain a known amount of activity of specific radionuclides. Although this technique has broad application, questions arise about the accuracy of results obtained using in vivo measurement methods and techniques. These questions might be resolved by developing computational phantoms representing the variation of radionuclide concentration in the human skeleton. These voxel geometries can be incorporated into a Monte Carlo code to estimate detector response. In this study, the United States Transuranium and Uranium Registries’ (USTUR) Case 0102 Am-241 Leg phantom was created using a real human skeleton. The phantom serves as a realistic standard for intercomparisons of whole body counting systems at US DOE facilities and other laboratories world-wide. The post mortem radiochemical analysis of the Case 0102 skeleton showed a significant variation of Am-241 concentration within and between different bones. This study describes an approach of modeling the radionuclide concentration distribution for use in a Monte Carlo simulation. A 3D voxel model of the phantom has been developed. DICOM (Digital Imaging and Communications in Medicine) images of the phantom have been segmented using Eclipse® radiotherapy planning software. Each Dicom image was segmented into multiple regions of interest. Additionally, all bones of the voxel phantom were divided into multiple sections to represent samples used in the radiochemical analysis. A method of simulating photon emission from the non-uniformly distributed Am-241 source is presented. Once the voxel representation of the phantom is imported into the Geant4 Monte Carlo code, experimental response of external planar germanium detectors can be simulated for various distributions of Am-241 concentration in the human bones of the phantom.
Validation of Proposed Revisions to ICRP Human Respiratory Tract Model Using Bioassay Data Associated with an Acute Inhalation of Refractory PuO2
M. Avtandilashvili (ISU), R. Brey (ISU), A. James (USTUR)
The International Commission on Radiological Protection (ICRP) is currently in the process of updating its biokinetic and dosimetric models, including the Human Respiratory Tract Model (HRTM). In order to account for the observed long-term retention of insoluble material in the lungs, Gregoratto et al. proposed a physiologically-based particle transport model that significantly simplifies the representation of particle clearance from alveolar-interstitial (AI) region. In proposed revision to the HRTM, the material deposited in the AI region is partitioned into just two clearance pathways: an “alveolar” compartment (A) is cleared only to the bronchioles and an “interstitial” compartment (I) is cleared only to the thoracic lymph nodes. This model was applied to the extensive bioassay data from the U.S. Transuranium and Uranium Registries’ (USTUR) tissue donors exposed to Refractory PuO2 during the 1965 plutonium fire accident at the Rocky Flats Plant. Case 0202 and Case 0407 are the two highest exposed of 18 USTUR tissue donors involved in this accident. The respiratory tract of the registrant 0202 was most likely compromised by his prior occupational exposure to coal dust, smoking habit and chronic obstructive pulmonary disease, while donor 0407 was a non-smoker and had no prior history of lung disorder. Bayesian analysis using the Weighted Likelihood Monte-Carlo Sampling (WeLMoS) method was performed in order to calculate the posterior probability distributions of critical model parameter values and dose estimates directly from the respective sets of bioassay and tissue analysis data. Similarities in and differences between the results for these two cases are discussed. It is demonstrated that, with appropriate adjustments, the simplified particle transport model proposed by Gregoratto et al. results in an acceptable fit to both USTUR data sets. The results of the study support the hypothesis that the PuO2 particles produced by the fire are extremely insoluble, with less than 1% absorbed relatively rapidly (at a rate of ~2 d-1) while the remainder is absorbed very slowly (at a rate of about 5 ´ 10-6 d-1 or less). Hence, the recommended dose coefficient for type S plutonium significantly underestimates the lung doses for this type of material.
Download ISU’s poster presentation titled, “Validation of Proposed Revisions to ICRP Human Respiratory Tract Model Using Bioassay Data Associated with an Acute Inhalation of Refractory PuO2” [USTUR-0310-11A]
Monte Carlo Simulation of In vivo Measurement of the Most Suitable Position of the Knee for the Most Accurate Measurement of the Activity
M. Khalaf (ISU), R. Brey (ISU), A. James (USTUR)
To assess the amount of radioactivity of certain radionuclide whose best indicators are low energy X-rays may be accomplished by a passive radioactive measurement of the knee. A correlation of the activity in the knee to that in the entire skeleton is possible. A question which arises is what is a suitable position of the leg by which all the knee bones contribute to detectable activity. The aim of this study was to create a new and valid model for Monte Carlo simulation of in vivo measurement of the knee to find an optimal position and therefore improve the validity of this measurement technique. CT scan images of the United States Transuranium and Uranium Registries (USTUR) case 0846 leg at different positions were obtained.These images were saved in DICOM format and they were segmented manually prior to voxelization and MCNP input. Monte Carlo modeling was employed to determine an optimized knee position; one that provides the best signal to noise ratio. Four different measurements of the USTUR 0846 leg knee in two different positions using a germanium detector were obtained. We noted that the best signal to noise ratio was observed with the leg in a bent positio and the detector close to the patella.