TAM-C - Internal Dosimetry Orlando VI 08:30 - 11:30
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| Chair(s): Dan Strom, John Klumpp
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TAM-C.1
08:30 Radon Recommendations: NCRP vs. ICRP NH Harley*, NYU School of Medicine
; Na Harley
Abstract: NCRP and ICRP are independent organizations that evaluate scientific information and provide guidance and recommendations for radiation protection. Both have proposed limits for occupational and residential 222Rn exposure, however ICRP is also used by many countries for regulatory purposes. NCRP was the first to publish a lung dose and risk model for 222Rn exposure and proposed a recommendation for personal exposure of <2 WLM per year corresponding to an estimated annual lung cancer risk of < 4x10-5. This exposure was half the annual US occupational exposure of 4 WLM adopted in 1971. In 1981, ICRP proposed an annual occupational limit of 4.8 WLM and in 1983 proposed an action level for intervention in homes between 3 and10 mSv per year or 0.9 and 2.6 WLM. The difficulty in going between concentration and dose limits is the use of a factor for dose conversion, known to be quite variable. In 2018, NCRP recommended that 222Rn concentration be reduced in dwellings and workplaces to < 300 Bq m-3 but no unique dose was associated except that an annual dose for this concentration lies between 1-20 mSv. In 2014, ICRP recommended an upper reference value of 300 Bq m-3 corresponding to an annual dose of 1-20 mSv but corresponds to an annual dose of 10 mSv when ICRP dose conversion units are used. The history, background and present dose factors are presented.
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TAM-C.2
08:45 Cylindrical Representations of Recycling Biokinetic Models DJ Strom*, Washington State University
; S Dumit, Los Alamos National Laboratory; M Avtandilashvili, Washington State University; SL McComish, Washington State University; G Tabatadze, Washington State University; SY Tolmachev, Washington State University; Strom
Abstract: 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.
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TAM-C.3
09:00 Macrodistribution of Plutonium among Dosimetric Compartments of the Human Respiratory Tract M Avtandilashvili*, USTUR, Washington State University
; SY Tolmachev, USTUR, Washington State University
Abstract: 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 of extensive data, published in peer-reviewed literature on retention and distribution of inhaled plutonium in different anatomical regions and segments of the human lungs, were obtained from autopsy studies of the Mayak Production Association workers. However, there are very limited data on plutonium distribution among the compartments of the ICRP HRTM. From a 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 individuals were smokers. Results indicated that plutonium was uniformly distributed among the dosimetric compartments. Plutonium distribution was independent of smoking status and plutonium material solubility type.
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TAM-C.4
09:15 Biokinetics of Pu-238 Oxides: Inferences from Bioassay Data D Poudel*, Radiation Protection Division, LANL
; L Bertelli, Radiation Protection Division, LANL; JA Klumpp, Radiation Protection Division, LANL; S Dumit, Radiation Protection Division, LANL; TL Waters, Radiation Protection Division, LANL
Abstract: The analysis of the bioassay data collected from several workers involved in different Pu-238 inhalation incidents at Los Alamos National Laboratory indicated the possibility of two competing mechanisms that could affect the intrinsic solubility of Pu-238 particles. The first is the fragmentation/dissolution mechanism, the consequence of which is a steadily increasing urinary excretion peaking around 2-3 years and gradually decreasing thereafter. The second is self-heating due to the decay heat of Pu-238, which results in slower-than-expected solubility. In many cases, modification of the default absorption parameters – those described in Occupational Intakes of Radionuclides (OIR): Part 4 – was necessary to describe the bioassay data. The urinary excretion patterns from all incidents and the corresponding dose coefficients have been calculated and compared.
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TAM-C.5
10:00 Investigation of a Plutonium 238 Skin Puncture Event SA Costigan*, Los Alamos National Laboratory
Abstract: On August 30, 2018 radiation protection (RP) personnel at Los Alamos National Laboratory (LANL) became aware that an individual had received an intake of Pu-238 via skin penetration at the LANL plutonium facility on August 18, 2018. While contaminated wounds are rare, this event was unique in LANL’s operational history in that no one, including the contaminated individual and responding personnel, recognized that a skin puncture had occurred. The original event was attributed to the penetration of a glove box glove and anti-contamination glove by a fine wire during maintenance activities causing low-level contamination of the skin surface. Due to the observed external skin contamination, the individual was placed on a special bioassay regimen. The first bioassay result was consistent with an intake and subsequent scanning for penetrating radiation identified Pu-238 activity in a microscopic wound. Further medical intervention including chelation and excision, bioassay sampling, and dose assessment ensued. A formal investigation was conducted which identified incident causes and judgements of need. Practical lessons learned have been applied to the LANL RP program resulting in process changes needed to prevent similar reoccurrences. This presentation provides an overview of the event including its causes and actions taken following discovery.
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TAM-C.6
10:15 Application of the Los Alamos Screening Wound Counter to a 238Pu Contaminated Wound MS Gadd*, LANL
Abstract: Rapid screening of potentially contaminated wounds is necessary to detect or confirm potential intakes via injection, to guide medical treatment, and provide information for follow-up bioassay monitoring. For assessment of wounds involving isotopes of plutonium and americium-241, Los Alamos National Laboratory (LANL) utilizes a thin thallium doped sodium iodide (NaI(Tl)) detector coupled to a multi-channel analyzer to detect and quantify the L x-ray and 59.54 keV photons from these isotopes. The counter is deployed at the LANL Occupational Medicine facility for assessment of potentially contaminated wounds and to help in guiding follow-up treatment if contamination is detected. This presentation will discuss the application of the Los Alamos Screening Wound Counter to a recent case involving a 238Pu injection that was not identified as a wound at the time of the incident. The intake was subsequently detected by an elevated bioassay sample. The counter was able to detect and confirm the presence 238Pu contamination at the suspected wound site, determine the location of the contamination, and perform measurements on excised tissue and the wound site to evaluate the efficacy of the excision.
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TAM-C.7
10:30 Case Study of a Wound Contaminated With 238Pu JA Klumpp*, Los Alamos National Laboratory
; L Bertelli, Los Alamos National Laboratory; D Poudel, Los Alamos National Laboratory
Abstract: This presentation considers operational aspects of a wound contaminated with 238Pu at Los Alamos National Laboratory. The incident initially appeared to be a simple external contamination, and radiation protection personnel were only alerted that an intake had happened by an elevated bioassay sample. Since there seemed to be no plausible mechanism of intake, the elevated sample was assumed to have been contaminated in the counting laboratory. However, a wound count using a NaI counter was ordered as a precaution, and discovered that a significant quantity of plutonium had been deposited beneath the skin, in spite of the fact that there was no visible wound. The contamination was excised and the employee was given a course of DTPA. We will discuss the unusual circumstances which caused the wound to go unnoticed, the interaction between radiation protection and medical personnel in managing the case, and the decision making process regarding when to discontinue chelation therapy.
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TAM-C.8
10:45 Historical Plutonium Contaminated Wound: Progression of the Calculated Dose During and After Chelation Treatment S Dumit*, Los Alamos National Laboratory
; G Miller, Retired (Santa Fe, NM); L Bertelli, Los Alamos National Laboratory; JA Klumpp, Los Alamos National Laboratory; D Poudel, Los Alamos National Laboratory; T Waters, Los Alamos National Laboratory
Abstract: Chelation treatment is typically administered following significant occupational intakes of plutonium. It could also be used as a medical countermeasure after nuclear accidents or terrorist attacks, or in the event of nuclear war. However, the treatment poses a dose assessment challenge due to the enhancement of the actinide’s rate of excretion, which alters its normal biokinetics. The radiation dose for USTUR case 0212 (plutonium-contaminated wound) has been previously calculated elsewhere. However, it was necessary for a waiting period of almost 1 year after the contamination incident to elapse because of the administration of chelation treatment. The present study re-evaluates the radiation dose of this historical case, using a full chelation model that can be applied to the bioassay data affected by chelation to assess the radiation dose during the course of administration of chelation treatments. To determine how early dose estimates obtained using this technique might have compared to later, more definitive estimates, the dose assessment in the present study is repeated at multiple time points (corresponding to bioassay measurements), from the early bioassay measurements until the final autopsy measurements. Preliminary results showed that the progression of dose and uncertainty gradually became smaller with time, due to the larger number of chelation treatments and the increased amount of data being used. It is interesting that the 1-year-out dose estimated with the chelation model, using cumulative urine and wound count data, is consistent with the previously-calculated 1-year dose, using 24-hour urine data more than 100 days after the final chelation. The method based on ignoring chelation-affected 24-hour urine data assumes that most dose is imparted late in time, while the chelation model makes no such assumption.
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TAM-C.9
11:00 Mitigating the Psychological Harm from Actinide Intakes JA Klumpp*, Los Alamos National Laboratory
; L Bertelli, Los Alamos National Laboratory; J Hoffman, Los Alamos National Laboratory; D Poudel, Los Alamos National Laboratory; T Waters, Los Alamos National Laboratory
Abstract: Investigations into possible actinide intakes, as well as the intakes themselves, may result in significant psychological harm that should be mitigated by the internal dosimetrist. Many aspects of this psychological impact are unique to actinide intakes and have not been discussed in the literature. In particular, employees may have difficulty understanding the lengthy dose assessment process, uncertain results, and committed doses. This presentation reviews some of these unique considerations and describes how the Internal Dosimetry Team at Los Alamos National Laboratory (LANL) has, with input and guidance from LANL psychologists, tried to address them. The presentation will discuss how harm can be prevented in advance through education, and mitigated following an incident or elevated routine bioassay through improved communication. Given the lack of reliable, publicly available resources pertaining to internal doses, and the complexity of internal dosimetry, it is important to provide educational resources which specifically deal with this topic.
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TAM-C.10
11:15 A Review of Computational Dosimetry for Intakes of Strontium-90 DW Jokisch*, Francis Marion University and Oak Ridge National Laboratory
Abstract: Strontium-90 is one of the more significant radionuclides of concern in releases of fission products to the environment. The radionuclide is also used in a variety of diagnostic and therapeutic applications. When taken into the body, the radionuclide’s biochemical behavior and physical half-life result in it spending long periods of time in the mineral portion of the skeleton. The skeleton creates a unique physical geometry for the moderate to high energy beta particles released by strontium-90 and its progeny given the size and proximity of bone marrow to the surrounding mineral bone. The current work reviews the history of computational methods for determining doses from intakes of strontium-90. Emphasis is placed on the unique contributions from the radionuclide’s progeny, yttrium-90. Dose coefficients from recent ICRP publications will be compared to previously published work. Comparisons will be made to past and present computational dosimetry methods in both medical and radiation protection applications.
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