60th Annual Health Physics Society Meeting, Indianapolis, IN, July 2015
USTUR faculty were authors on three platform presentations, which were given at the 60th Annual Health Physics Society Meeting in Indianapolis, IN, July 12-16, 2015.
Modeling Uranium Hexafluoride Inhalation
Maia Avtandilashvili (USTUR), Matthew Puncher (Public Health England), Stacey McComish (USTUR), Sergei Tolmachev (USTUR)
The U.S. Transuranium and Uranium Registries' whole-body donor (Case 1031) was exposed to a single acute inhalation of uranium hexafluoride (UF6) produced from an explosion at a processing facility. Inductively coupled plasma mass-spectrometric analysis of tissue samples collected at the autopsy 65 y after the accident indicated unusually long-term retention of inhaled slightly-enriched uranium material (0.85% 235U) in the deep lungs and thoracic lymph nodes inconsistent with the International Commission on Radiological Protection (ICRP) human respiratory tract model predictions for soluble uranium compounds. The tissue measurement and bioassay monitoring data from this case were analyzed with the ICRP biokinetic models using both conventional (maximum likelihood) and Bayesian statistical analysis methods. Maximum likelihood analysis using the current ICRP human respiratory tract model resulted in an estimated intake of 79 mg of uranium composed of 86% soluble, Type F material and 14% insoluble, Type S material. For the Bayesian approach, the Markov Chain Monte Carlo (MCMC) method was applied to the data to estimate posterior probability distributions of intake and case-specific lung model parameters, using the revised human respiratory tract model that is being used by ICRP to calculate revised effective dose coefficients for workers. The MCMC results were fairly consistent with the maximum likelihood analysis, supporting the fact that the inhaled uranium material was predominantly Type F with a small but significant Type S component: 95% posterior ranges of the rapid fraction and slow dissolution rate were 0.12-0.91, and 0.00022‐0.00036 d-1 with the median values at 0.37 and 0.00031 d-1, respectively. The derived posterior distributions of dissolution parameter values were used to calculate the corresponding 95% range of effective dose per unit intake of uranium resulting from inhalation of the UF6 mixture. It was demonstrated that the ICRP effective dose coefficient recommended for UF6 was located below the lower 2.5%-quantile of this range. Hence, the use of the dissolution parameter values obtained here may be more appropriate for radiation protection purposes when individuals are exposed to a UF6 mixture that contains an insoluble uranium component.
Radionuclide distribution measurement within anatomical bone structures using digital autoradiography
George Tabatadze (USTUR), Brian Miller (PNNL), Sergei Tolmachev (USTUR)
The ionizing-radiation Quantum Imaging Detector (iQID) is a radiation camera originally developed for gamma-ray imaging applications such as scintigraphy and single-photon emission computed tomography. Recently, the detector's response was extended to a broader range of ionizing radiation, including: neutrons, spontaneous fission, conversion electrons, alpha and beta-particles. The iQID digital autoradiography imager allows for real‐time quantitative autoradiography at a resolution up to 20 μm when imaging alpha particles. With conventional autoradiography technique, imaging may take up to several months without knowledge that a sufficient number of decays has occurred to visualize the spatial distribution of alpha emitters. Quantification of the activity can also be difficult or impractical. The iQID allows studying radionuclide microdistribution in the anatomical bone structures, such as cortical and trabecular bone volumes and surfaces at sub mBq levels. The initial feasibility imaging experiments were performed using bone samples from individuals exposed to radium (Ra-226), plutonium (Pu-239), and americium (Am-241). The bone samples are available at the National Human Radiobiology Tissue Repository (NHRTR), which is a part of the U.S. Transuranium and Uranium Registries (USTUR). For the internally deposited Ra-226, Pu-239, and Am-241, activity distribution was visualized and quantified in various bone sections. Radionuclide activity distribution ranged between 0.002 and 0.003 mBq mm-2 for Pu-239, 0.1 and 0.7 mBq mm-2 for Ra-226, and 1.0 and 10.0 mBq mm-2 for Am-241. The initial feasibility studies are promising and prompt for additional sample imaging, especially those with small-scale heterogeneous distributions where traditional counting methods do not apply.
Quantitative Single-Particle Digital Autoradiography with the ionizing-Radiation Quantum Imaging Detector
Brian Miller (PNNL), George Tabatadze (USTUR), Michael Dion (PNNL), Sofia Frost (Fred Hutchinson Cancer Research Center), Johnnie Orozco (Fred Hutchinson Cancer Research Center), Oliver Press (Fred Hutchinson Cancer Research Center), Brenda Sandmaier (Fred Hutchinson Cancer Research Center), Matthias Miederer (Johannes Gutenberg University, Germany), Christoph Brochhausen (Johannes Gutenberg University, Germany), Sergei Tolmachev (USTUR)
Presented is a novel digital autoradiography camera and imaging methodology called iQID ionizing radiation Quantum Imaging Detector). The imager comprises a scintillator in direct contact with a micro-channel plate (MCP) image intensifier and a lens for imaging the intensifier screen on to a CCD or CMOS camera sensor, all within a compact light-tight enclosure. iQID is sensitive to a broad range of radiation including gamma-/X-rays, neutrons, spontaneous fission, conversion electrons, alpha and beta particles. Individual photons or particles absorbed in the scintillator crystal or phosphor screen produce a flash of light that is amplified via the image intensifier by a factor of 104-106 and then imaged on to the camera. Scintillation flashes associated with individual events are finely sampled with an array of pixels and referred to as an event cluster. iQID's ability to localize charged particles, both spatially and temporally, on an event-by-event basis enables alpha-particle radioactivity distributions to be quantified at millibecquerel-levels in small volumes, e.g., 10 × 10 × 10 μm3, even with short-lived isotopes. Images are constructed in real time at high spatial resolutions with an unrestricted dynamic range. The intrinsic spatial resolution of the detector has been measured to levels as high as 20 μm with alphas. iQID is a portable, laptop-operated system that requires no cooling and leverages the ever-increasing advances in CCD and CMOS camera sensor technology. The most recent system developed uses a 4-megapixel camera (2048 × 2048 pixels) that acquires full-resolution images at rates up to 90 frames per second. Large-area iQID configurations (up to 200 mm diameter) accommodate autoradiography studies requiring simultaneous imaging of an array of tissue sections. An overview of the technology and recent imaging studies with alpha (239Pu, 241Am, 226Ra, 232Th, and 211At) and beta emitters (90Y and 177Lu) will be presented that demonstrate the application of iQID as an integral imaging tool for radiobiology applications and microdosimetry in targeted radionuclide therapy.
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