THAM-C - Dose Reconstruction and Radiation Effects Orlando VI 10:00 - 12:30
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| Chair(s): Wesley Bolch, Joseph Shonka
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THAM-C.1
10:00 Estimation of Lifetime Doses to the Public Living Close to NPPs Using Electron Paramagnetic Resonance (EPR) Measurements on Extracted Tooth Enamel L Ghimire*, University of Ontario Institute of Technology
; E Waller, University of Ontario Institute of Technology
Abstract: There are uncertainties in the low dose (less than 100mGy) measurements in tooth enamel dosimetry and those uncertainties need to be minimized to determine a low dose with high precision and accuracy using X-band EPR spectroscopy. Some studies have shown that chronic low dose radiation may have adverse health effects when exposure occurs over a long period. But still it is unclear about the effects of chronic low dose radiation to the local population and the environment. Thus, there are worries and concerns regarding the exposure of low dose radiation from anthropogenic sources. One of the main challenges in a low dose measurement using EPR tooth enamel dosimetry is the sample preparation and the EPR analysis to achieve high precision, accuracy and reproducibility of the results. This presentation discusses the EPR (x-band) spectral acquisition and measurement algorithm used to determine the anthropogenic low dose radiation that people get by being in close proximity to Nuclear Generating Stations (NGSs). The measurement technique (algorithm) eliminates the background and noise from the tubes and resonator which might interfere with a low dose signal and performs the g-factor calibration using the marker accessary (E4100MK) for a precise dose measurement in tooth enamel. The spectrometer calibration and sensitivity (i.e., both sample related and instrument related) are optimized prior to the analysis. At the same time, the background dose (DBG), total dose from the ultraviolet (UV) radiation in incisor teeth (DUV), radiation dose from diagnostic and medical dental procedure (DX?ray) are subtracted to calculate the total anthropogenic dose (DT) in a local population with high accuracy. The uncertainty of the dose is calculated by subtracting contributions from impurities in tooth enamel, instabilities in an EPR spectrometer, errors due to variations in enamel sensitivity and uncertainties in calibration curve slope determination. The factor affecting the precision and accuracy in the low dose EPR tooth enamel dosimetry and the advantages and disadvantages of the EPR techniques in a low dose radiation research are discussed.
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THAM-C.2
10:15 Dosimetric Impact of a New Computational Voxel Phantom Series for the Japanese Atomic Bomb Survivors: Children and Adults K Griffin, National Cancer Institute
; C Paulbeck, University of Florida; WE Bolch*, University of Florida; H Cullings, Radiation Effects Research Foundation; S Egbert, Consultant; S Funamoto, Radiation Effects Research Foundation; T Sato, Japan Atomic Energy Agency; A Endo, Atomic Energy Agency; N Hertel, Georgia Institute of Technology; C Lee, National Cancer Institute
Abstract: One of the largest sources of data on radiation exposure to human beings lies in the study of the atomic bomb survivors at Hiroshima and Nagasaki, Japan performed by the Radiation Effects Research Foundation (RERF). As part of their retrospective dosimetry efforts for the atomic bomb survivors, RERF has published two core systems: Dosimetry System 1986 (DS86) and Dosimetry System 2002 (DS02). Due to computing limitations of the time, only three stylized phantoms were used in DS86 and DS02 to represent the entire Japanese population: an infant, child, and adult. Our study aimed to evaluate the dosimetric impact that should be expected from using an updated and age-expanded phantom series with the survivor cohort. To this end, we developed a new series of hybrid phantoms, based on the Japanese population of 1945, which has greater anatomical realism and improved age resolution over those used by RERF. These phantoms were converted to voxel format and compared to their older counterparts through the calculation of organ dose coefficients using DS02 free-in-air particle fluences at three distances from bomb hypocenter. From the photon portion of the spectra, organ dose differences of up to nearly 25% are expected between the old and new series, while organ dose differences of up to nearly 70% are expected from the neutron portion. We also compared organ dose coefficients amongst themselves to determine the accuracy in the use of one organ dose as the epidemiological surrogate to another. Certain organ-surrogate pairs were shown to be inappropriate, such as using the colon dose for breast risk analyses. Overall, our new series of phantoms provides significant improvements to survivor organ dosimetry, especially to those survivors who were previously misrepresented in body size by their stylized phantom and to those who experienced a highly-directional irradiation field.
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THAM-C.3
10:30 DOSIMETRIC IMPACT OF A NEW COMPUTATIONAL VOXEL PHANTOM SERIES FOR THE JAPANESE ATOMIC BOMB SURVIVORS: PREGNANT FEMALES CJ Paulbeck*, UF
; K Griffin, NCI; L Choonsik, NCI; H Cullings, RERF; S Egbert; S Funamoto, RERF; T Sato, JAEA; A Endo, JAEA; N Hertel, Georgia Tech; W Bolch, UF
Abstract: An important cohort of the atomic bomb survivors are pregnant females, as well as their children who were exposed in-utero. Estimates of organ dose to the developing fetus thus allow for the development of dose and gestation age-dependent models of deterministic (e.g., organ malformation) and stochastic (e.g., leukemia) risk of in-utero exposure. To date, both the 1986 and 2002 dosimetry systems at the Radiation Effects Research Foundation have utilized the uterine wall in the non-pregnant adult female as a dose surrogate for fetal organs and tissues. In this study, we present a new J45 (Japan 1945) series of phantoms of the adult pregnant female at 8-weeks, 15-weeks, 25-weeks, and 38-weeks post-conception. These models were derived from their UF phantom counterparts but have been rescaled to approximate the pregnant mother using 1945 Japanese morphometry data. Fetal and maternal organ doses were estimated by computationally exposing the pregnant female phantom series to DS02 free-in-air photon and neutron fluences at three distances from the hypocenter at both Hiroshima and Nagasaki under frontal (AP) and isotropic (ISO) particle incidence. For the fetal organ doses, our results indicate that the uterine wall of the non-pregnant female generally underestimates fetal organ dose within the pregnant female. The magnitude of these differences varies with both radiation type and irradiation geometry, with the smallest differences (5-7%) seen for ISO photon fields and the largest differences (20-30%) seen for AP neutron fields. Significant discrepancies were seen in fetal brain dose and its uterine wall surrogate, particularly for photon AP fields (ratio of uterine wall to brain dose varied from 0.9 to 1.3) and neutron AP fields (dose ratios from 0.75 to 2.0). These results demonstrate that the J45 pregnant female phantom series offers the opportunity for significant improvements in fetal organ dose assessment within this unique cohort of the atomic bomb survivors.
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THAM-C.4
10:45 Uncertainty of Dose Factors for Bone Marrow Dosimetry of Bone-seeking Sr-90 and Sr-89 E Shishkina*, Urals Research Center for Radiation Medicine, URCRM
; A Volchkova, Urals Research Center for Radiation Medicine, URCRM; P Sharagin, Urals Research Center for Radiation Medicine, URCRM; M Smith, Pacific Northwest National Laboratory, Richland, Washington, USA; M Degteva, Urals Research Center for Radiation Medicine, URCRM; B Napier, Pacific Northwest National Laboratory, Richland, Washington, USA
Abstract: Evaluation of bone marrow doses from 89/90Sr incorporated in trabecular and cortical bone is very important for enhancements in the Techa River Dosimetry System (TRDS). For dosimetric modeling of bone marrow, conversion factors (DFs) are needed from radionuclide concentration in bone tissues to dose in active marrow. Analysis of DF uncertainties is necessary for the development of a stochastic version of the TRDS providing both dose estimates and associated overall uncertainty. The purpose of this study was to evaluate the uncertainties of bone marrow dose factors for 89/90Sr incorporated in the trabecular and cortical bone tissues. For this purpose, parametric random generation of computational phantoms of bone segments of different dimensions was performed. Electron transport in bone segments for 90Sr+90Y and 89Sr beta spectra were simulated and dose factors were calculated. This study presents an analysis of computational results and evaluation of uncertainty due to bone segmentation and shape stylization. The effect of individual variability of bone dimensions was also considered.
Systematic error resulting from restriction of electron-photon transport in spongiosa was evaluated. Uncertainty of the correction does not exceed 5%. Uncertainty induced by stylization of irregularly shaped bones does not exceed 15%. Segment-specific uncertainties due to individual variability vary from 12% to 45% depending on individual variability of dimensions of different bones. Skeletal-average DF variability for the adult male can be described by a lognormal distribution with coefficients of variation equal to 24% and 27% for trabecular and cortical bone contamination, respectively.
*This work was funded by the U.S. Department of Energy’s Russian Health Studies Program and the Federal Medical Biological Agency of the Russian Federation under the auspices of the Joint Coordinating Committee for Radiation Effects Research Project 1.1, Techa River Population Dosimetry.
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THAM-C.5
11:00 The First Dirty Bomb, Trinity JJ Shonka, SRA
Abstract: The Trinity test in 1945 was similar to what might occur with a dirty bomb. A fraction of the plutonium was used in the explosion. The device was detonated at low altitude, on a 100-foot steel tower. As a result, the fireball contacted the soil. Because of the low altitude, fallout exhibited a “skip distance” with little fallout near the test site. Although there were plans for evacuation, radio communication was lost as the survey teams traveled out to follow the overhead plume. Thus, the command center was unsure of whether that the criteria had been met (15R/hr; 75R/2 weeks) and failed to order the evacuation. The population in New Mexico was ten times closer than those downwind from the NTS. Cattle on the Chupadera Mesa received 20,000 R skin exposure from the fallout. Potential doses to downwinders will be summarized, along with one person’s personal experience.
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THAM-C.6
11:15 CANCELLED Health Effects from Exposure to Thorium LS Keith*, ATSDR
; L Ingerman, SRC; DW Wohlers, SRC; MD Brooks, ATSDR; PA Charp, ATSDR
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THAM-C.7
11:30 Limitations of Cause of Death Data Among Autopsied Population in the United States Transuranium and Uranium Registries SL McComish*, U.S. Transuranium and Uranium Registries, Washington State University
; J Zhou, Office of Domestic and International Health Studies, U.S. Department of Energy; FT Martinez, U.S. Transuranium and Uranium Registries, Washington State University; SY Tolmachev, U.S. Transuranium and Uranium Registries, Washington State University
Abstract: The United States Transuranium and Uranium Registries (USTUR) is a human tissue program that studies the biokinetics and internal dosimetry of actinides – such as uranium, plutonium, and americium – in former nuclear workers who were occupationally exposed to these elements. Tissue donors were predominantly Caucasian males, who volunteered portions of their bodies, or their whole bodies, for scientific use posthumously. The causes of death among 356 USTUR Registrants were determined, and a preliminary analysis of discrepancies between death certificates and autopsy findings was conducted. Although the USTUR population is not a representative sample of U.S. nuclear workers due to self-selection, it provides valuable information such as the accuracy of death certificates among this autopsied population.
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THAM-C.8
11:45 Case Studies in Brain Dosimetry for Internally Deposited Radionuclides SY Tolmachev*, US Transuranium and Uranium Registries, Washington State University
; RW Leggett, Oak Ridge National Laboratory; M Avtandilashvili, US Transuranium and Uranium Registries, Washington State University; JD Boice, Jr, National Council on Radiation Protection and Measurements
Abstract: Element-specific biokinetic models are used to reconstruct radiation doses to systemic tissues from internally deposited radionuclides. These models typically represent explicitly only those tissues that tend to dominate the systemic behaviour of the element over time. The remaining tissues are aggregated into a pool called Other tissue in which activity is assumed to be uniformly distributed. Explicitly identified tissues usually consist of some subset of the tissues: liver, kidneys, bone, bone marrow, gonads, thyroid, spleen, and skin. The brain is included explicitly in systemic biokinetic models for a few elements; however, it is typically addressed as an implicit mass fraction of Other tissue. There is increasing interest in potential adverse effects of internal emitters, particularly alpha emitters, on the brain as limited analogues for galactic cosmic ray exposures during space travel. The Million Person Study is estimating brain doses from exposure to radionuclides and evaluating dementia, Alzheimer’s disease, Parkinson’s disease, and motor neuron disease as possible adverse outcomes of combined high- and low-LET exposures to brain tissue. This paper summarizes an assessment of potential improvements in brain dosimetry for internal emitters from explicit modelling of brain biokinetics in place of treating the brain as an implicit mass fraction of Other tissue. Comparisons are made of dose coefficients for selected radionuclides based on alternate versions of the systemic biokinetic model for each radionuclide, differing only in the handling of brain tissue.
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