Health Physics

Boice, John D.; Ellis, Elizabeth D.; Golden, Ashley P.; Girardi, David J.; Cohen, Sarah S.; Chen, Heidi; Mumma, Michael T.; Shore, Roy E.; Leggett, Richard W.

doi: 10.1097/HP.0000000000000825pmid: 29481528

Abstract The purpose of this paper is to present an overview of ongoing work on the Million Worker Study (MWS), highlighting some of the key methods and progress so far as exemplified by the study of workers at the Mallinckrodt Chemical Works (MCW). The MWS began nearly 25 y ago and continues in a stepwise fashion, evaluating one study cohort at a time. It includes workers from U.S. Department of Energy (DOE) Manhattan Project facilities, U.S. Nuclear Regulatory Commission (NRC) regulated nuclear power plants, industrial radiographers, U.S. Department of Defense (DoD) nuclear weapons test participants, and physicians and technologists working with medical radiation. The purpose is to fill the major gap in radiation protection and science: What is the risk when exposure is received gradually over time rather than briefly as for the atomic bomb survivors? Studies published or planned in 2018 include leukemia (and dosimetry) among atomic veterans, leukemia among nuclear power plant workers, mortality among workers at the MCW, and a comprehensive National Council on Radiation Protection and Measurements (NCRP) Report on dosimetry for the MWS. MCW has a singular place in history: the 40 tons (T) of uranium oxide produced at MCW were used by Enrico Fermi on 2 December 1942 to produce the first manmade sustained and controlled nuclear reaction, and the atomic age was born. Seventy-six years later, the authors followed the over 2,500 MCW workers for mortality and reconstructed dose from six sources of exposure: external gamma rays from the radioactive elements in pitchblende; medical x rays from occupationally required chest examinations; intakes of pitchblende (uranium, radium, and silica) measured by urine samples; radon breath analyses and dust surveys overseen by Robley Evans and Merril Eisenbud; occupational exposures received before and after employment at MCW; and cumulative radon concentrations and lung dose from the decay of radium in the work environment. The unique exposure reconstructions allow for multiple evaluations, including estimates of silica dust. The study results are relevant today. For example, NASA is interested that radium, deposited in the brain, releases high-LET alpha particles - the only human analogue, though limited, for high energy, high-Z particles (galactic cosmic rays) traveling through space that might affect astronauts on Mars missions. Don’t discount the past; it’s the prologue to the future!

Ellis, Elizabeth D.; Boice, John D.; Golden, Ashley P.; Girardi, David J.; Cohen, Sarah S.; Mumma, Michael T.; Shore, Roy E.; Leggett, Richard W.; Kerr, George D.

doi: 10.1097/HP.0000000000000847pmid: 29481529

Abstract Mallinckrodt Chemical Works was the earliest uranium processing facility in the Manhattan Project, beginning in 1942. Even then, concern existed about possible health effects resulting from exposure to radiation and pitchblende dust. This concern was well founded as the facility processed Belgian Congo pitchblende ore that was up to 60% pure uranium with high 235U content and up to 100 mg of radium per ton. Workers were exposed to external gamma radiation plus internal radiation from inhalation and ingestion of pitchblende dust (uranium, radium, and silica). Multiple sources of exposure were available for organ dose reconstruction to a degree unique for an epidemiologic study. Personal film badge measures available from 1945 captured external exposures. Additional external exposure included 15,518 occupational medical x-rays and 210 radiation exposure records from other facilities outside of Mallinckrodt employment. Organ dose calculations considered organ-specific coefficients that account for photon energy and job-specific orientation of workers to the radiation source during processing. Intakes of uranium and radium were based on 39,451 uranium urine bioassays and 2,341 breath radon measurements, and International Commission on Radiological Protection (ICRP) Publication 68 biokinetic models were used to estimate organ-specific radiation absorbed dose. Estimates of exposure to airborne radon and its short-lived progeny were based on radon measurements in work areas where radium-containing materials were handled or stored, together with estimated exposure times in these areas based on job titles. Dose estimates for radon and its short-lived progeny were based on models and methods recently recommended in ICRP Publication 137. This comprehensive dosimetric approach follows methods outlined by the National Council on Radiation Protection Scientific Committee 6‐9 for the Million Worker Study. Annual doses were calculated for six organs: lung, brain, heart, kidney, colon and red bone marrow. Evaluation and adjustment for individual cumulative measures of pitchblende dust inhalation were made for lung and kidney diseases.

Harley, Naomi H.

doi: 10.1097/HP.0000000000000828pmid: 29481530

Abstract Guidelines for occupational exposure to radiation are based on annual absorbed or effective dose. Guidelines for 222Rn exposure are currently based on air concentrations of 222Rn or decay products. Models of bronchial dose from decay product exposure are based on calculations that have five major parameters with parameter variabilities ranging from 20 to 50%. Many countries currently use the ICRP dose conversion convention, which is a ratio of lifetime 222Rn lung cancer risk to lifetime atomic bomb dose risk. The results of ongoing epidemiology changed both lifetime risk values, and the dose conversion convention has increased by a factor of 2. Therefore, the current dose conversion convention risk ratio is to be replaced by biokinetic dosimetric models. The main effect of variability in the value of 222Rn dose factors on industry is that the workplace atmosphere must be characterized accurately, and at present, this is not possible. A history of the dose factor models is central to factor development. The values of the dose model parameters are described illustrating the difficulty in calculation of a dose factor with universal applicability. The objective is to show the range of each parameter and the effect of the dose factor used when reporting occupational or residential bronchial dose.

Minter, Kelsey M.; Jannik, G. Timothy; Stagich, Brooke H.; Dixon, Kenneth L.; Newton, Joseph R.

doi: 10.1097/HP.0000000000000835pmid: 29481531

Abstract The U.S. Environmental Protection Agency (EPA) requires the use of the model CAP88 to estimate the total effective dose (TED) to an offsite maximally exposed individual (MEI) for demonstrating compliance with 40 CFR 61, Subpart H: The National Emission Standards for Hazardous Air Pollutants (NESHAP) regulations. For NESHAP compliance at the Savannah River Site (SRS), the EPA, the U.S. Department of Energy (DOE), South Carolina’s Department of Health and Environmental Control, and SRS approved a dose assessment method in 1991 that models all radiological emissions as if originating from a generalized center of site (COS) location at two allowable stack heights (0 m and 61 m). However, due to changes in SRS missions, radiological emissions are no longer evenly distributed about the COS. An area-specific simulation of the 2015 SRS radiological airborne emissions was conducted to compare to the current COS method. The results produced a slightly higher dose estimate (2.97 × 10−4 mSv vs. 2.22 × 10−4 mSv), marginally changed the overall MEI location, and noted that H-Area tritium emissions dominated the dose. Thus, an H-Area dose model was executed as a potential simplification of the area-specific simulation by adopting the COS methodology and modeling all site emissions from a single location in H-Area using six stack heights that reference stacks specific to the tritium production facilities within H-Area. This “H-Area Tritium Stacks” method produced a small increase in TED estimates (3.03 × 10−4 mSv vs. 2.97 × 10−4 mSv) when compared to the area-specific simulation. This suggests that the current COS method is still appropriate for demonstrating compliance with NESHAP regulations but that changing to the H-Area Tritium Stacks assessment method may now be a more appropriate representation of operations at SRS.

O’Mara, Ryan; Hayes, Robert

doi: 10.1097/HP.0000000000000843pmid: 29481532

Abstract In nuclear forensics or accident dosimetry, building materials such as bricks can be used to retrospectively determine radiation fields using thermoluminescence and/or optically stimulated luminescence. A major problem with brick material is that significant chemical processing is generally necessary to isolate the quartz from the brick. In this study, a simplified treatment process has been tested in an effort to lessen the processing burden for retrospective dosimetry studies. It was found that by using thermoluminescence responses, the dose deposition profile of a brick sample could be reconstructed without any chemical treatment. This method was tested by estimating the gamma-ray energies of an 241Am source from the dose deposition in a brick. The results demonstrated the ability to retrospectively measure the source energy with an overall energy resolution of approximately 6 keV. This technique has the potential to greatly expedite dose reconstructions in the wake of nuclear accidents or for any related application where doses of interest are large compared to overall process system noise.

Barrett, Christina; Hellickson, Ivy; Ben-Avi, Lily; Lamb, Dayna; Krahenbuhl, Melinda; Cerveny, Kara L.

doi: 10.1097/HP.0000000000000788pmid: 29481533

Abstract Ionizing radiation (IR) has been linked to multiple types of cellular responses, but its effects on developing organisms are still poorly understood. The authors investigated whether zebrafish embryos exhibit differential responses relative to IR dose and developmental age at time of exposure. Early-stage zebrafish embryos were exposed to different levels of gamma radiation and then, at varying points after irradiation, assayed for morphological defects and levels of cell death. To quantify in vivo cellular responses to low-dose IR exposure and explore how tissue-specific cell functions affect radiation response, apoptotic cells were counted in three regions: the tail, urogenital papilla, and left eye. The authors found that increased gamma radiation doses correlated with increased levels of apoptosis in the developing tail and eye, whereas cells of the urogenital papilla appeared to undergo apoptosis independently of radiation dose. This suggests that the linear-no-threshold model may not be appropriate in all contexts. Grouping embryos by age at IR exposure revealed that gamma radiation exposure resulted in higher levels of apoptosis in embryos irradiated at 2 d post fertilization (dpf), suggesting a radiosensitive stage of development. Moreover, levels of apoptosis were statistically influenced by days grown after irradiation, with embryos fixed at later stages showing more dramatic apoptotic responses to radiation exposure. This latency to effect suggests potential competition between DNA repair and apoptosis pathways, which may lead to the accumulation of apoptotic cells only after an initial lag period.

Brown, Steven H.; Chambers, Douglas B.

doi: 10.1097/HP.0000000000000786pmid: 29481534

Abstract Two traditional methods are used, often in combination, for assessing the intake and resulting dose from the inhalation of radioactive aerosols. The first calculates the intake based on air sampling programs and assessing and assigning dose using published dose conversion factors. The second approach assigns dose from the results of bioassay programs using measurements of radionuclides in human excreta (ex vivo, sometimes referred to as “in vitro”) or via direct measurements of radionuclides in the body (in vivo) in combination with metabolic models. This paper describes standard practices using each of these methods to assess and assign worker dose from inhalation of uranium products produced at natural uranium processing facilities, namely uranium mills and in-situ uranium recovery facilities (ISRs). Chemical speciation is an important consideration, which relates directly to solubility in body fluids and associated metabolic behavior. The concepts are illustrated by specific examples applicable to the products to which workers can be exposed at natural uranium processing facilities.

Misdaq, M.A.; Aitayoub, A.; Chaouqi, A.

doi: 10.1097/HP.0000000000000777pmid: 29481535

Abstract Consumption of seafoods has increased during the last two decades in many countries. In Morocco, annual fresh marine fish consumption has increased significantly due to the existence of modern fish markets in major cities. To explore the exposure pathway of 238U, 232Th, 222Rn, and 220Rn radionuclides to the human body of consumers, these radionuclides were measured in various fresh and canned marine fish samples widely consumed by the Moroccan population by using two types of solid state nuclear track detectors (SSNTDs). A census was taken of the fresh and canned marine fish consumed by adult members of the public and building material workers. Committed equivalent doses due to annual intakes of 238U, 232Th, 222Rn, and 220Rn were determined in the organs of adult members of the urban Moroccan population from the ingestion of fresh and canned marine fish samples. The influence of pollution caused by building material dusts on committed effective doses to workers due to the 238U, 232Th, 222Rn, and 220Rn radionuclides from the ingestion of canned fish samples was investigated.

Bednarz, Bryan; Grudzinski, Joseph; Marsh, Ian; Besemer, Abby; Baiu, Dana; Weichert, Jamey; Otto, Mario

doi: 10.1097/HP.0000000000000789pmid: 29481536

Abstract There is a growing need to estimate the absorbed dose to small animals from preclinical investigations involving diagnostic and therapeutic radiopharmaceuticals. This paper introduces a Monte Carlo-based dosimetry platform called RAPID, which is capable of calculating murine-specific three-dimensional (3D) dose distributions. A comparison is performed between absorbed doses calculated with RAPID and absorbed doses calculated in a commonly used reference mouse phantom called MOBY. Four test mice containing different xenografts underwent serial PET/CT imaging using a novel diagnostic therapy (theranostic) agent NM404, which can be labeled with 124I for imaging or 131I for therapy. Using the PET/CT data, 3D dose distributions from 131I-NM404 were calculated in the mice using RAPID. Mean organ doses in these four test mice were compared to mean organ doses derived by using two previously published 131I S-values datasets in MOBY. In addition, mean tumor doses calculated in RAPID were compared to mean organ doses derived from unit density spheres. Large differences were identified between mean organ doses calculated in the test mice using RAPID and those derived in the MOBY phantom. Mean absorbed dose percent errors in organs ranged between 0.3% and 333%. Overall, mass scaling improved agreement between MOBY phantom calculations and RAPID, where percent errors were all less than 26%, with the exception of the lung in which percent errors reached values of 48%. Percent errors in mean tumor doses in the test mice and unit density spheres were less pronounced but still ranged between 8% and 23%. This work demonstrates the limitations of using pre-computed S-values in computational phantoms to predict organ doses in small animals from theranostic procedures. RAPID can generate accurate 3D dose distributions in small animals and in turn offer much greater insight on the ability of a given theranostic agent to image and treat diseases.

Bramlitt, Edward T.

doi: 10.1097/HP.0000000000000829pmid: 29481537