An age- and sex-specific biokinetic model for radon.

Publication 137 of the International Commission on Radiological Protection (ICRP) describes a biokinetic model for radon used to derive dose coefficients for occupational intake of radon isotopes. The model depicts transfer of inhaled or ingested radon to blood, exchange of radon between blood and tissues, and gradual loss of radon from the body based on physical laws governing transfer of a non-reactive and soluble gas between materials. This paper describes an age- and sex-specific variation of that model developed for use in an upcoming ICRP series of reports on environmental intake of radionuclides by members of the public titled 'Dose Coefficients for Intakes of Radionuclides by Members of the Public'. The proposed model modifies the model structure and transfer coefficients presented in Publication 137 to allow more realistic dosimetric treatment of bone marrow and breast and expands the model to address pre-adult ages, based on the physical principles used in the development of the model of Publication 137 together with anatomical and physiological changes occurring during human development.

Dose reconstruction for plutonium-239 intakes at the Rocky Flats Plant.

PURPOSE: The Rocky Flats (RF) Plant was a weapons manufacturing facility that operated from the early 1950s to 1989. Its primary missions were the production of plutonium (Pu) pits for thermonuclear weapons and the processing of retired weapons for Pu recovery. The purpose of this study was to estimate radiation doses to a cohort of 4499 RF workers from an intake of 239Pu, the primary plutonium isotope handled at the site. MATERIALS AND METHODS: The latest biokinetic models of the International Commission on Radiological Protection, or site-specific variations of those models, were used to estimate 239Pu intakes for each worker based on model fits to bioassay data often coupled with lung measurements. RESULTS: Urinary excretion and lung retention data for most 239Pu intakes could be fit reasonably well by a mixture of Pu dioxide and moderately soluble material. For some workers, better fits were obtained by application of other absorption types including Type S, 239Pu nitrate, or pure 239Pu dioxide, or by assuming intake via a wound. The lungs typically received the highest tissue doses, with fifty-year committed equivalent doses in the range of 0.5-1 Sv for 275 workers, 1-5 Sv for 115 workers, and greater than 5 Sv for 12 workers. CONCLUSIONS: RF was a unique site regarding a large number of lung measurements available for determining the appropriate absorption types for inhaled material. This provided higher confidence in reconstructed 239Pu doses than is generally gained from urinary data alone.

Measurable radiation levels around individuals externally contaminated by nuclear fallout‡.

During the early response to large-scale radioactive contamination events, people who are potentially affected need to be screened for radioactive contamination and public health staff need to triage individuals who may need immediate decontamination. This is typically done by screening individuals for external contamination using ionising radiation detection equipment. In this study, spatially and temporally dependent isotopic compositions from a simulated nuclear detonation and Monte Carlo methods were used to relate contamination activity levels to the measurable radiation levels at select distances away from an individual with whole-body contamination. Radionuclide-specific air kerma rate coefficients and Geiger-Mueller instrument response coefficients at five select distances from contaminated individuals are presented for 662 radionuclides. Temporally and spatially dependent incident-specific coefficients are presented for a hypothetical surface detonation of a 235U-fueled device.

Methods of improving brain dose estimates for internally deposited radionuclides.

The US National Council on Radiation Protection and Measurements (NCRP) convened Scientific Committee 6-12 (SC 6-12) to examine methods for improving dose estimates for brain tissue for internally deposited radionuclides, with emphasis on alpha emitters. This Memorandum summarises the main findings of SC 6-12 described in the recently published NCRP Commentary No. 31, 'Development of Kinetic and Anatomical Models for Brain Dosimetry for Internally Deposited Radionuclides'. The Commentary examines the extent to which dose estimates for the brain could be improved through increased realism in the biokinetic and dosimetric models currently used in radiation protection and epidemiology. A limitation of most of the current element-specific systemic biokinetic models is the absence of brain as an explicitly identified source region with its unique rate(s) of exchange of the element with blood. The brain is usually included in a large source region calledOtherthat contains all tissues not considered major repositories for the element. In effect, all tissues inOtherare assigned a common set of exchange rates with blood. A limitation of current dosimetric models for internal emitters is that activity in the brain is treated as a well-mixed pool, although more sophisticated models allowing consideration of different activity concentrations in different regions of the brain have been proposed. Case studies for 18 internal emitters indicate that brain dose estimates using current dosimetric models may change substantially (by a factor of 5 or more), or may change only modestly, by addition of a sub-model of the brain in the biokinetic model, with transfer rates based on results of published biokinetic studies and autopsy data for the element of interest. As a starting place for improving brain dose estimates, development of biokinetic models with explicit sub-models of the brain (when sufficient biokinetic data are available) is underway for radionuclides frequently encountered in radiation epidemiology. A longer-term goal is development of coordinated biokinetic and dosimetric models that address the distribution of major radioelements among radiosensitive brain tissues.

Basis for the ICRP's updated biokinetic model for systemic astatine.

The International Commission on Radiological Protection (ICRP) recently updated its biokinetic models for workers in a series of reports called the OIR (occupational intakes of radionuclides) series. A new biokinetic model for astatine (At), the heaviest member of the halogen family, was adopted in OIR Part 5 (ICRP in press). Occupational intakes of radionuclides: Part 5). This paper provides an overview of available biokinetic data for At; describes the basis for the ICRP's updated model for At; and tabulates dose coefficients for intravenous injection of each of the two longest lived and most important At isotopes,211At and210At. At-211 (T1/2= 7.214 h) is a promising radionuclide for use in targetedα-particle therapy due to several favourable properties including its half-life and the absence of progeny that could deliver significant radiation doses outside the region ofα-particle therapy. At-210 (T1/2= 8.1 h) is an impurity generated in the production of211At in a cyclotron and represents a potential radiation hazard via its long-lived progeny210Po (T1/2= 138 days). Tissue dose coefficients for injected210At and211At based on the updated model are shown to differ considerably from values based on the ICRP's previous model for At, particularly for the thyroid, stomach wall, salivary glands, lungs, spleen, and kidneys.

A million persons, a million dreams: a vision for a national center of radiation epidemiology and biology.

BACKGROUND: Epidemiologic studies of radiation-exposed populations form the basis for human safety standards. They also help shape public health policy and evidence-based health practices by identifying and quantifying health risks of exposure in defined populations. For more than a century, epidemiologists have studied the consequences of radiation exposures, yet the health effects of low levels delivered at a low-dose rate remain equivocal. MATERIALS AND METHODS: The Million Person Study (MPS) of U.S. Radiation Workers and Veterans was designed to examine health effects following chronic exposures in contrast with brief exposures as experienced by the Japanese atomic bomb survivors. Radiation associations for rare cancers, intakes of radionuclides, and differences between men and women are being evaluated, as well as noncancers such as cardiovascular disease and conditions such as dementia and cognitive function. The first international symposium, held November 6, 2020, provided a broad overview of the MPS. Representatives from four U.S. government agencies addressed the importance of this research for their respective missions: U.S. Department of Energy (DOE), the Centers for Disease Control and Prevention (CDC), the U.S. Department of Defense (DOD), and the National Aeronautics and Space Administration (NASA). The major components of the MPS were discussed and recent findings summarized. The importance of radiation dosimetry, an essential feature of each MPS investigation, was emphasized. RESULTS: The seven components of the MPS are DOE workers, nuclear weapons test participants, nuclear power plant workers, industrial radiographers, medical radiation workers, nuclear submariners, other U.S. Navy personnel, and radium dial painters. The MPS cohorts include tens of thousands of workers with elevated intakes of alpha particle emitters for which organ-specific doses are determined. Findings to date for chronic radiation exposure suggest that leukemia risk is lower than after acute exposure; lung cancer risk is much lower and there is little difference in risks between men and women; an increase in ischemic heart disease is yet to be seen; esophageal cancer is frequently elevated but not myelodysplastic syndrome; and Parkinson's disease may be associated with radiation exposure. CONCLUSIONS: The MPS has provided provocative insights into the possible range of health effects following low-level chronic radiation exposure. When the 34 MPS cohorts are completed and combined, a powerful evaluation of radiation-effects will be possible. This final article in the MPS special issue summarizes the findings to date and the possibilities for the future. A National Center for Radiation Epidemiology and Biology is envisioned.

Mortality among workers at the Los Alamos National Laboratory, 1943-2017.

BACKGROUND: During World War II (WWII), the Manhattan Engineering District established a secret laboratory in the mountains of northern New Mexico. The mission was to design, construct and test the first atomic weapon, nicknamed 'The Gadget' that was detonated at the TRINITY site in Alamogordo, NM. After WWII, nuclear weapons research continued, and the laboratory became the Los Alamos National Laboratory (LANL). MATERIALS AND METHODS: The mortality experience of 26,328 workers first employed between 1943 and 1980 at LANL was determined through 2017. Included were 6157 contract workers employed by the ZIA Company. Organ dose estimates for each worker considered all sources of exposure, notably photons, neutrons, tritium, 238Pu and 239Pu. Vital status determination included searches within the National Death Index, Social Security Administration and New Mexico State Mortality Files. Standardized Mortality Ratios (SMR) and Cox regression models were used in the analyses. RESULTS: Most workers (55%) were hired before 1960, 38% had a college degree, 25% were female, 81% white, 13% Hispanic and 60% had died. Vital status was complete, with only 0.1% lost to follow-up. The mean dose to the lung for the 17,053 workers monitored for radiation was 28.6 weighted-mGy (maximum 16.8 weighted-Gy) assuming a Dose Weighting Factor of 20 for alpha particle dose to lung. The Excess Relative Risk (ERR) at 100 weighted-mGy was 0.01 (95%CI -0.02, 0.03; n = 839) for lung cancer. The ERR at 100 mGy was -0.43 (95%CI -1.11, 0.24; n = 160) for leukemia other than chronic lymphocytic leukemia (CLL), -0.06 (95%CI -0.16, 0.04; n = 3043) for ischemic heart disease (IHD), and 0.29 (95%CI 0.02, 0.55; n = 106) for esophageal cancer. Among the 6499 workers with measurable intakes of plutonium, an increase in bone cancer (SMR 2.44; 95%CI 0.98, 5.03; n = 7) was related to dose. The SMR for berylliosis was significantly high, based on 4 deaths. SMRs for Hispanic workers were significantly high for cancers of the stomach and liver, cirrhosis of the liver, nonmalignant kidney disease and diabetes, but the excesses were not related to radiation dose. CONCLUSIONS: There was little evidence that radiation increased the risk of lung cancer or leukemia. Esophageal cancer was associated with radiation, and plutonium intakes were linked to an increase of bone cancer. IHD was not associated with radiation dose. More precise evaluations will await the pooled analysis of workers with similar exposures such as at Rocky Flats, Savannah River and Hanford.

A biokinetic model for systemic sodium.

This paper describes an updated biokinetic model for systemic sodium (Na), developed for use in a series of reports by the International Commission on Radiological Protection (ICRP) on occupational intake of radionuclides. In contrast to the ICRP's previous model for intake of radio-sodium by workers, the updated model depicts realistic directions of movement of Na in the body including recycling of activity between blood and tissues. The updated model structure facilitates extension of the baseline transfer coefficients for adults to different age groups and to special exposure scenarios such as transfer of radio-sodium from the mother to the foetus or the nursing infant. Dose coefficients for22Na and24Na based on the updated model generally do not differ greatly from those based on the ICRP's previous Na model when both models are connected to the ICRP's latest dosimetry system. The main exception is that the updated model yields roughly twofold higher dose coefficients for endosteal bone surface than does the previous model due to the dosimetrically cautious assumption in the updated model that exchangeable Na in bone resides on bone surface.

COEFFICIENTS FOR ESTIMATING PRENATAL DOSE IN PREGNANT WORKERS FROM ACUTE INTAKES.

Inhalation and ingestion dose coefficients for the embryo and fetus from intakes of radionuclides by the mother are provided in the International Commission on Radiological Protection (ICRP) Publication 88 for intake of each of 74 radionuclides. To address the many other possible radionuclides to which workers may be exposed, effective dose coefficients were developed for the embryo/fetus for all additional radionuclides addressed in ICRP Publication 107 with half-life of 10 min or more. The general approach was to use the estimated dose to the mother's uterus during pregnancy as a scalable proxy for the dose to the embryo/fetus. The set of scaling factors used in the study was derived from analyses of the relationships of the dose to the mother's uterus and the effective dose to the embryo/fetus for the ~400 cases (considering two intake modes and multiple forms of many of the radionuclides) addressed in Publication 88.

Biokinetic models for group IVB elements.

The International Commission on Radiological Protection (ICRP) is updating its biokinetic models in a series of reports titled Occupational Intakes of Radionuclides (OIR series). This paper provides an overview of biokinetic data for the group IVB elements hafnium (Hf) and titanium (Ti), compares these data with findings for the more extensively studied Group IVB element zirconium (Zr), and proposes biokinetic models for systemic Hf and Ti for use in the OIR series. The biokinetic model for systemic Zr adopted in OIR Part 2 (ICRP, 2016a) is proposed for application to Hf in view of the nearly identical chemical and physical properties of these two elements, their closely similar behavior in the environment, and their nearly identical biokinetic properties suggested by available comparative data. The model structure applied to Zr and Hf is also applied to Ti, but a separate set of transfer coefficients is proposed for Ti.