Health Physics Society Meeting, Orlando, FL, July 7-11, 2019
USTUR faculty members were authors on four presentations at the 64th Annual Health Physics Society Meeting in July 2019. Additionally, adjunct professor Daniel Strom gave a continuing education lecture (CEL) on the importance of the measurand in Health Physics.
Case studies in brain dosimetry for internally deposited radionuclides
Sergei Y. Tolmachev (USTUR), Richard W. Leggett (ORNL), Maia Avtandilashvili (USTUR), John D. Boice, Jr. (Vanderbilt University)
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 but typically is addressed as an implicit mass fraction of Other tissue. There is increasing interest in the potential adverse effects of internal emitters, particularly alpha emitters, on the brain as limited analogues for galactic cosmic ray exposures during space travel and for possible assessment of radiogenic effects on brain in nuclear medicine patients and radiation workers. 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. [USTUR-0520-19A]
Macrodistribution of plutonium among dosimetric compartments of the human respiratory tract
Maia Avtandilashvili (USTUR), Sergei Y. Tolmachev (USTUR)
The International Commission on Radiological Protection (ICRP) Publication 66 human respiratory tract model (HRTM) and its revised version published in ICRP Publication 130 divide the thoracic region of the lungs into three compartments: bronchial (BB), bronchiolar (bb), and alveolar-interstitial (AI). Human lungs consist of five anatomical lobes. Each lobe contains tissues from all three dosimetric compartments.
Most extensive data published in the peer-reviewed literature on retention and distribution of inhaled plutonium in different anatomical regions and segments of the human lungs were obtained from the autopsy studies of the Mayak PA workers. However, there are very limited data on plutonium distribution among compartments of the ICRP HRTM. From dosimetry standpoint, information on plutonium retention in BB, bb and AI compartments is critical.
In this study, the lungs from four US Transuranium and Uranium Registries’ (USTUR) tissue donors were dissected based on the ICRP human respiratory tract model and radiochemically analyzed. Plutonium activity was measured separately in BB, bb and AI. Three of these donors had documented inhalation intake of soluble plutonium nitrate while the fourth individual inhaled very insoluble, refractory PuO2 particles. Two of these four individuals were smokers. Results indicated that plutonium was uniformly distributed among dosimetric compartments. Plutonium distribution was independent of smoking status and plutonium material solubility type. [USTUR-0522-19A]
Limitations of cause of death data among autopsied population in the United States Transuranium and Uranium Registries
Stacey L. McComish (USTUR), Joey Zhou (DOE), Florencio T. Martinez (USTUR), Sergei Y. Tolmachev (USTUR)
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. [USTUR-0519-19A]
Cylindrical representations of recycling biokinetic models
Daniel J. Strom (USTUR), Sara Dumit (USTUR), Maia Avtandilashvili (USTUR), Stacey L. McComish (USTUR), George Tabatadze (USTUR), Sergei Y. Tolmachev (USTUR)
In 2018, the USTUR developed a cylindrical representation of the Leggett et al. (2005) recycling model describing the biokinetics of systemic plutonium. That visualization is updated to incorporate the International Commission on Radiological Protection (ICRP) human alimentary tract model (HATM) in place of the “GI Tract” compartment, which required assuming that uptake from the small intestine goes into the Blood 2 compartment rather than the Blood 1 compartment. New cylindrical visualizations are presented for recycling models for uranium and americium based on the ICRP publication series on occupational intakes of radionuclides (OIR). The OIR publications or drafts currently show these models with “GI Tract” compartments; in this work, the HATM has been used in place of the GI tract in the uranium and americium models. Extensions of the models to include an explicit compartment for brain have also been developed, since the effects of high-linear energy transfer radiation on the brain are of interest to those studying the effects of space radiation on astronauts. The insights provided by these novel representations are discussed. [USTUR-0521-19A]
CEL: The importance of the measurand in health physics
Daniel J. Strom (USTUR)
When making a measurement for radiation protection or regulatory compliance, what is “the quantity intended to be measured?” That phrase is the definition of “measurand” that appears in the latest version of the International Vocabulary of Metrology (the VIM). For example, one may conduct a counting experiment to determine the amount of activity in a sample or the amount of activity in a lake. These two different measurands come with differing assumptions, although they may be based on the same measurement result. Another example is the distinction between the result of a measurement in counts per second and the measurand in becquerels (or cpm versus dpm). Alas, most US writing, such as ANSI standards, regulations, MARLAP, and MARSSIM, ignores the concept of the measurand, making it very difficult to convey concepts such as minimum detectable amount, a terribly misleading name for the smallest usually detectable measurand (SUDM). The concept of measurand gives clearer meaning to the notions of population parameter (a measurand) and sample parameter (one or more measurement results or inferences based on those results). When the concepts of variability, uncertainty, bias, error and blunder are combined with models used to make inferences about measurands, or probabilistic statements about measurands using Bayes’s theorem, the distinction between measurement results and measurands is key. While the measurand has sometimes been called the “true value,” those words are not adequate in understanding metrology. All health physicists need to be able to state what the measurand is for every measurement result they make or use. [USTUR-0523-19P]