The 61st Annual Meeting of the Health Physics Society

17-21 July 2016, Spokane, WA

Single Session

[Schedule Grid]

TAM-A1 - Technical Session I: USTUR Internal Research

100 C   10:30 - 12:00

Chair(s): Carol Iddins, Dunstana Melo
TAM-A1.1   10:30  Estimation of Actinide Skeletal Content from a Single Bone Analysis SY Tolmachev*, USTUR, Washington State University ; RL Kathren, Washington State University

Abstract: Estimation of the total skeletal actinide content (Ask) is important to support biokinetic modeling of actinides. Ask is calculated as a product of radionuclide activity concentration (Crad) and skeletal weight (Wsk), Ask = Crad � Wsk. The large uncertainties are typically associated with the estimated activity, as generally only few bones are analyzed and ICRP reference weight of 10.5 kg or height-weight equation are used to estimate the skeleton weight. Several approaches are published for plutonium and americium activities estimation in a human skeleton based on the analyses of limited number of bones collected at autopsy and various assumptions on skeleton weight. Alternatively, Ask can be estimated from a single bone analysis if a fraction of total skeleton activity (deposition coefficient, Kdep) is known for this particular bone. The use of Kdep = Abone/Ask, allows simple straightforward calculation of total skeleton activity from a single bone analysis with reduced uncertainties. In addition, a linear regression equation, Ask = a�Abone + b, can be used. In this study, Kdep values were calculated for patella bone using data from 16 whole body donors to the United States Transuranium and Uranium Registries (USTUR) with known exposure to 238Pu, 239Pu, and 241Am. Total 238Pu, 239Pu, and 241Am skeletal activities were calculated using a standardized methodology. The average Kdep values (±standard deviation) for 238Pu, 239Pu, and 241Am were calculated as 0.0037±0.0015, 0.0033±0.0012, and 0.0040±0.0013, respectively. With repeated ANOVA test, no significant difference was found among Kdep for 238Pu, 239Pu, and 241Am (p=0.126) resulting in the average Kdep = 0.0037±0.0013 (n=48) for the actinides. Thus, the measured activity of plutonium or americium in patella can be reliably used to estimate the total skeletal content. Actinide total skeletal content can be simply obtained by multiplying the measured activity in the patella by 1/Kdep = 273±98. Using linear regression analysis for log-transformed data (n=48), the excellent correlation, with a slope of 0.957±0.023, and 2.411±0.036 intercept, was found between activity in patella and that in the skeleton (r2=0.973).

TAM-A1.2   10:45  Updating ICRP 70 Skeleton Weight vs. Body Height Equation M Avtandilashvili*, USTUR, Washington State University ; SY Tolmachev, USTUR, Washington State University

Abstract: A total skeletal activity is one of the fundamental quantities for modeling biokinetics of bone-seeking radionuclides. The uncertainty in the activity estimates depends on the precision of radionuclide bone concentration measurements and the accuracy of the calculated skeleton weights. This is a challenging task, especially if only limited number of bones are collected and analyzed and no prior information on skeleton weight is available. In 1995, the International Commission on Radiological Protection (ICRP) published the skeleton weight vs. body height equation, W(kg) = 10.7 + 0.119 x H(cm), based upon data from 31 male individuals including two US Transuranium and Uranium Registries (USTUR) whole-body donors. Currently, data are available from additional USTUR whole-body donations that provide a unique opportunity to update the ICRP 70 equation. In this study, the total skeleton weights were estimated for 39 male whole-body donors, including 2 previously used by ICRP. All skeleton weights were calculated using a standardized approach and corrected for bilateral asymmetry, and possible bone mass losses during dissection. Body heights were based upon autopsy reports (when available) or medical examination records. To update the skeleton weight vs. body height correlation, original ICRP 70 and new USTUR data were combined in a set of 68 data points representing a group of 25 to 90+ year old individuals. For this group, body heights and skeleton weights ranged from 155 to 188 cm and 6.5 to 13.4 kg, respectively. Data were fitted with a linear least-square regression. A significant correlation between two parameters was observed (r = 0.55), and a new skeleton weight vs. body height equation was derived: W(kg) = 6.65 + 0.094 x H(cm). This equation will be used to estimate the skeleton weights and, ultimately, total skeletal actinide activities for biokinetic modeling of the USTUR partial-body donation cases.

TAM-A1.3   11:00  USTUR Case 0785: Modeling Pu Decorporation Following Complex Exposure. S Dumit*, USTUR, Washington State University ; M Avtandilashvili, USTUR, Washington State University; B Breustedt, Karlsruhe Institute of Technology; SY Tolmachev, USTUR, Washington State University

Abstract: High levels of exposure to actinides can cause severe health effects. Individuals with significant internal contamination typically undergo treatment with chelating agents to accelerate urinary excretion and thus reduce radiation dose to sensitive tissues. The US Transuranium and Uranium Registries (USTUR) studies actinide biokinetics and tissue dosimetry by following up occupationally exposed workers. These studies are fundamental to improving the reliability of, and confidence in, radiation dose and risk assessment methods. By linking radiation exposure history, bioassay results, and medical data with post-mortem measurements of actinides in the human body, we aim to develop and parameterize a biokinetic model for plutonium decorporation therapy. USTUR Case 0785 was selected for this study. This individual was exposed to plutonium via inhalation and wounds due to an explosion at the defense nuclear facility, and underwent chelation treatment. Worksite personnel estimated his systemic deposition at 7.4 kBq. The 239Pu whole-body activity at the time of death, estimated from tissue radiochemical analysis, was 2.8 kBq. Of these, 69.7% was deposited in the skeleton, 21.7% in the liver, and 6.5% in the respiratory tract. The results confirmed that internal deposition of plutonium was caused by inhalation and wound intake, and provided additional information on material solubility type. In this preliminary study, IMBA Professional Plus software was applied to fit post-mortem plutonium activities measured in the lungs, liver and skeleton. The ICRP 130 human respiratory tract model, NCRP 156 wound model, and Leggett plutonium systemic model were used with default assumptions of material type. As small particles are typically generated due to explosion, 1 µm particle size was used instead of ICRP 130’s default value of 5 µm. Inhalation and wound intake regimes were fitted simultaneously. Results of calculations were consistent with the ICRP 68 Type S material. The residual fraction of total intake, not removed by chelation treatment, was estimated at approximately 24 kBq with 89% contributed by inhalation. This information will be used for modeling plutonium decorporation therapy.

TAM-A1.4   11:15  Digital Autoradiography of Am-241 Spatial Distribution within Trabecular Bone Regions G Tabatadze*, USTUR, Washington State University ; BW Miller, Pacific Northwest National Laboratory. University of Arizona; SY Tolmachev, USTUR, Washington State University

Abstract: The ionizing-radiation Quantum Imaging Detector (iQID) is used at the United States Transuranium and Uranium Registries (USTUR) for imaging Alpha-emitters: Am-241, Pu-239, and Ra-226. The iQID allows visualizing the distribution of Alpha-particle events and differentiating between the surface-seeker (Am, Pu) and bone volume-seeker (Ra) radionuclides and their activity quantification. In this study, spatial distribution of metabolized Am-241 within trabecular bone regions was investigated using USTUR Case 0846 (voluntary donor). For this individual, initial Am-241 whole-body deposition was estimated to be 66.6 kBq. Post-mortem radiochemical analysis indicated that 29.6 kBq were retained in the skeleton 40 years post exposure. Bone specimens were sampled from humerus proximal end, humerus proximal shaft, and clavicle acromial end. These specimens were embedded in methyl methacrylate plastic and processed to produce multiple 100µm-thick sections. Bone sections were polished to a fine surface and anatomical structure images were taken with a digital microscope. All bone sections were imaged at 35 µm resolution for at least two weeks. In order to evaluate the radionuclide distribution and corresponding histology precisely, iQID images were co-registered and superimposed with the anatomical structure images. The Am-241 activity distributions were visualized and quantified in cortical bone and trabecular spongiosa. These two bone regions are well represented within the humerus proximal end. High activity concentration of Am-241 was measured in trabecular bone region. Activity concentration ratio was used to represent radionuclide distribution within different bone regions. The cortical bone-to-trabecular spongiosa activity concentration ratio of 1:0.7 was calculated for the humerus proximal end. This is in agreement with ratios obtained from radiochemical analysis 1:0.7 and ICRP biokinetic model predictions 1:0.5. The cortical-to-trabecular bone activity concentration ratio of 1:2.7 was in agreement with that of 1:3 obtained from radiochemical analysis. This quantitative digital autoradiography imaging approach is proven to be an effective method for micro-scale heterogeneous distribution studies, where traditional counting methods do not apply.

TAM-A1.5   11:30  Reanalysis of Radiation and Mesothelioma in the U.S. Transuranium and Uranium Registries JY Zhou*, U.S. Department of Energy ; SL McComish, USTUR, Washington State University; SY Tolmachev, USTUR, Washington State University

Abstract: It has been noted for years that there is an excess of mesothelioma deaths among the Registrants of the U.S. Transuranium and Uranium Registries (USTUR). The previous analyses to link the excess of mesothelioma to radiation were done inappropriately in part due to the small number of mesothelioma cases and the use of the U.S. general population as a comparison group. The reanalysis applied an internally matched case control approach to evaluate the cluster of mesothelioma cases in association with cumulative external radiation exposures. First, all causes of USTUR Registrants� deaths were classified into 4 groups: mesothelioma cases (Meso), lung cancers (LC), other cancers (OC), and non-cancers (NC). Second, for each case of mesothelioma, controls were identified in the LC (2 ~ 3 controls per case), OC (2 ~ 5 controls per case), and NC (2 ~ 5 controls per case) groups matching gender (male), race (white), years of employment (± 2.5 years), first hire (± 5 years), birth year (±5), and age at death (±5 years). Third, a paired t-test (one sided) was used to examine whether there were statistically significant differences in cumulative external radiation doses between cases in Meso group and respective controls in LC, OC, and NC groups. In practice, a permutation paired t-test (PPTT) was developed to run the significance tests based on a large number of paired t-tests. For each paired t-test, one control for each case was randomly selected from multiple (2 ~5 controls per case) matching controls. This procedure was repeated at least 5,000 times, and the percentage of statistically significant (p � 0.05) paired t-tests was counted. Inference was reached based on whether or not 5% or more of PPTTs were statistically significant. PPTTs were not significant for Meso vs. LC, and Meso vs. OC; PPTTs were significant, however, for Meso vs. NC with larger than 9.0% of significant paired t-tests. A follow up conditional logistic regression for the Meso and NC groups showed a non-statistically significant odd ratio (OR) of 1.001 (95% CI: 0.997 ~ 1.006) between cumulative external radiation doses and mesothelioma. The internally matched case control analysis suggested that the excess of mesothelioma deaths among USTUR Registrants was not associated with cumulative external radiation exposures.

TAM-A1.6   11:45  Open Discussion

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