Dose Estimation for Exposure to Radioactive Fallout from Nuclear Detonations.

ABSTRACT: In recent years, the prospects that a nuclear device might be detonated due to a regional or global political conflict, by violation of present nuclear weapons test ban agreements, or due to an act of terrorism, has increased. Thus, the need exists for a well conceptualized, well described, and internally consistent methodology for dose estimation that takes full advantage of the experience gained over the last 70 y in both measurement technology and dose assessment methodology. Here, the models, rationale, and data needed for a detailed state-of-the-art dose assessment for exposure to radioactive fallout from nuclear detonations discussed in five companion papers are summarized. These five papers present methods and data for estimating radionuclide deposition of fallout radionuclides, internal and external dose from the deposited fallout, and discussion of the uncertainties in the assessed doses. In addition, this paper includes a brief discussion of secondary issues related to assessments of radiation dose from fallout. The intention of this work is to provide a usable and consistent methodology for both prospective and retrospective assessments of exposure from radioactive fallout from a nuclear detonation.

A Method for Estimating the Deposition Density of Fallout on the Ground and on Vegetation from a Low-yield, Low-altitude Nuclear Detonation.

ABSTRACT: This paper describes a relatively simple model developed from observations of local fallout from US and USSR nuclear tests that allows reasonable estimates to be made of the deposition density (activity per unit area) on both the ground and on vegetation for each radionuclide of interest produced in a nuclear fission detonation as a function of location and time after the explosion. In addition to accounting for decay rate and in-growth of radionuclides, the model accounts for the fractionation (modification of the relative activity of various fission and activation products in fallout relative to that produced in the explosion) that results from differences in the condensation temperatures of the various fission and activation products produced in the explosion. The proposed methodology can be used to estimate the deposition density of all fallout radionuclides produced in a low yield, low altitude fission detonation that contribute significantly to dose. The method requires only data from post-detonation measurements of exposure rate (or beta or a specific nuclide activity) and fallout time-of-arrival. These deposition-density estimates allow retrospective as well as rapid prospective estimates to be made of both external and internal radiation exposure to downwind populations living within a few hundred kilometers of ground zero, as described in the companion papers in this volume.

A Methodology for Estimating External Doses to Individuals and Populations Exposed to Radioactive Fallout from Nuclear Detonations.

ABSTRACT: A methodology of assessment of the doses from external irradiation resulting from the ground deposition of radioactive debris (fallout) from a nuclear detonation is proposed in this paper. The input data used to apply this methodology for a particular location are the outdoor exposure rate at any time after deposition of fallout and the time-of-arrival of fallout, as indicated and discussed in a companion paper titled "A Method for Estimating the Deposition Density of Fallout on the Ground and on Vegetation from a Low-yield Low-altitude Nuclear Detonation." Example doses are estimated for several age categories and for all radiosensitive organs and tissues identified in the most recent ICRP publications. Doses are calculated for the first year after the detonation, when more than 90% of the external dose is delivered for populations close to the detonation site over a time period of 70 y, which is intended to represent the lifetime dose. Modeled doses in their simplest form assume no environmental remediation, though modifications can be introduced. Two types of dose assessment are considered: (1) initial, for a rapid but only approximate dose estimation soon after the nuclear detonation; and (2) improved, for a later, more accurate, dose assessment following the analysis of post-detonation measurements of radiation exposure and fallout deposition and the access of information on the lifestyle of the exposed population.

A Methodology for Calculation of Internal Dose Following Exposure to Radioactive Fallout from the Detonation of a Nuclear Fission Device.

ABSTRACT: The purpose of this paper is to provide a methodology for the calculation of internal doses of radiation following exposure to radioactive fallout from the detonation of a nuclear fission device. Reliance is on methodology previously published in the open literature or in reports not readily available, though some new analysis is also included. Herein, we present two methodologic variations: one simpler to implement, the other more difficult but more flexible. The intention is to provide in one place a comprehensive methodology. Pathways considered are (1) the ingestion of vegetables and fruits contaminated by fallout directly, (2) the ingestion of vegetables and fruits contaminated by continuing deposition by rain- or irrigation-splash and resuspension, (3) the ingestion of vegetables and fruits contaminated by absorption of radionuclides by roots after tillage of soil, (4) the non-equilibrium transfer of short-lived radionuclides through the cow-milk and goat-milk food chains, (5) the equilibrium transfer of long lived radionuclides through milk and meat food chains, and (6) inhalation of descending fallout. Uncertainty in calculated results is considered. This is one of six companion papers that describe a comprehensive methodology for assessing both external and internal dose following exposures to fallout from a nuclear detonation. Input required to implement the dose-estimation model for any particular location consists of an estimate of the post-detonation external gamma-exposure rate and an estimate of the time of arrival of the fallout cloud. The additional data required to make such calculations are included in the six companion papers.

Parameter Values for Estimation of Internal Doses from Ingestion of Radioactive Fallout from Nuclear Detonations.

ABSTRACT: This paper suggests values or probability distributions for a variety of parameters used in estimating internal doses from radioactive fallout due to ingestion of food. Parameters include those needed to assess the interception and initial retention of radionuclides by vegetation, translocation of deposited radionuclides to edible plant parts, root uptake by plants, transfer of radionuclides from vegetation into milk and meat, transfer of radionuclides into non-agricultural plants and wildlife, and transfer from food and drinking water to mother's milk (human breast milk). The paper includes discussions of the weathering half-life for contamination on plant surfaces, biological half-lives of organisms, food processing (culinary factors), and contamination of drinking water. As appropriate, and as information exists, parameter values or distributions are specific for elements, chemical forms, plant types, or other relevant characteristics. Information has been obtained from the open literature and from publications of the International Atomic Energy Agency. These values and probability distributions are intended to be generic; they should be reviewed for applicability to a given location, time period, or season of the year, as appropriate. In particular, agricultural practices and dietary habits may vary considerably both with geography and over time in a given location.

Dosimetry and uncertainty approaches for the million person study of low-dose radiation health effects: overview of the recommendations in NCRP Report No. 178.

PURPOSE: Scientific Committee 6-9 was established by the National Council on Radiation Protection and Measurements (NCRP), charged to provide guidance in the derivation of organ doses and their uncertainty, and produced a report, NCRP Report No. 178, Deriving Organ Doses and their Uncertainty for Epidemiologic Studies with a focus on the Million Person Study of Low-Dose Radiation Health Effects (MPS). This review summarizes the conclusions and recommendations of NCRP Report No. 178, with a concentration on and overview of the dosimetry and uncertainty approaches for the cohorts in the MPS, along with guidelines regarding the essential approaches used to estimate organ doses and their uncertainties (from external and internal sources) within the framework of an epidemiologic study. CONCLUSIONS: The success of the MPS is tied to the validity of the dose reconstruction approaches to provide realistic estimates of organ-specific radiation absorbed doses that are as accurate and precise as possible and to properly evaluate their accompanying uncertainties. The dosimetry aspects for the MPS are challenging in that they address diverse exposure scenarios for diverse occupational groups being studied over a period of up to 70 y. Specific dosimetric reconstruction issues differ among the varied exposed populations that are considered: atomic veterans, U.S. Department of Energy workers exposed to both penetrating radiation and intakes of radionuclides, nuclear power plant workers, medical radiation workers, and industrial radiographers. While a major source of radiation exposure to the study population comes from external gamma- or x-ray sources, for some of the study groups, there is also a meaningful component of radionuclide intakes that requires internal radiation dosimetry assessments.

Dosimetry associated with veterans who participated in nuclear weapons testing.

BACKGROUND: This article summarizes the methodology, results, and challenges of the reconstruction of red bone marrow and male breast doses for a 1982-person sub-cohort of ∼114,270 U.S. military veterans who participated in eight atmospheric nuclear weapons tests between 1945 and 1962. These doses are being used in an epidemiological investigation of leukemia and male breast cancer as part of a study of one million U.S. persons to investigate risk from chronic low-dose radiation exposure. METHODS: Previous doses to these veterans had been estimated for compensation and tended to be biased high but newly available documentation made calculating individual doses and uncertainties using detailed exposure scenarios for each veteran possible. The techniques outlined in this report detail the methodology for developing individual scenarios and accounting for bias and uncertainty in dose based on the assumptions made about exposure. RESULTS: Doses to the atomic veterans in this sub-cohort were relatively low, with about two-thirds receiving red bone marrow doses <5 mGy and only four individuals receiving a red bone marrow dose >50 mGy. The average red bone marrow dose for members of the sub-cohort was 5.9 mGy. Doses to male breast were approximately 20% higher than red bone marrow doses. DISCUSSION AND CHALLENGES: Relatively low uncertainty was achieved as a result of our methodology for reconstructing exposures based on knowledge of the individual veterans' locations and activities from military records. Challenges did arise from use of military records to determine probability of participation in specific activities but accounted for in estimates of uncertainty.

Asbestos exposure and mesothelioma mortality among atomic veterans.

BACKGROUND: The United States (U.S.) conducted 230 above-ground atmospheric nuclear weapons tests between 1945 and 1962 involving over 250,000 military personnel. This is the first quantitative assessment of asbestos-related mesothelioma, including cancers of the pleura and peritoneum, among military personnel who participated in above-ground nuclear weapons testing. METHODS: Approximately 114,000 atomic veterans were selected for an epidemiological study because they were in one of eight series of weapons tests that were associated with somewhat higher personnel exposures than the other tests and because they have been previously studied. We were able to categorize specific jobs into potential for asbestos exposure based on a detailed database of the military activities of the atomic veterans. Standardized mortality ratios (SMR) were calculated by service, rank (officer/enlisted) and ratings (occupation code and work location aboard ship) after 65 years of follow-up. RESULTS: Mesothelioma deaths were significantly increased overall (SMR 1.56; 95% CI 1.32-1.82; n = 153). This increase was seen only among those serving in the PPG (SMR 1.97; 95% CI 1.65-2.34; n = 134), enlisted men (SMR 1.81; 95% CI 1.53-2.13; n = 145), and the 70,309 navy personnel (SMR 2.15; 95% CI 1.80-2.56; n = 130). No increased mortality rates were seen among the other services: army (SMR 0.45), air force (SMR 0.85), or marines (SMR 0.75). Job categories with the highest potential for asbestos exposure (machinist's mates, boiler technicians, water tender, pipe fitters, and fireman) had an of SMR 6.47. Job categories with lower potential (SMR =1.35) or no potential (SMR =1.28) for asbestos exposure had non-significantly elevated mesothelioma mortality. CONCLUSIONS: The large excess of mesothelioma deaths seen among atomic veterans was explained by asbestos exposure among enlisted naval personnel. The sources of exposure were determined to be on navy ships in areas (or with materials) with known asbestos content. No excess of mesothelioma was observed in other services or among naval personnel with minimal exposure to asbestos in this low-dose radiation exposed cohort.

Mortality among U.S. military participants at eight aboveground nuclear weapons test series.

BACKGROUND: Approximately 235,000 military personnel participated at one of 230 U.S. atmospheric nuclear weapons tests from 1945 through 1962. At the Nevada Test Site (NTS), the atomic veterans participated in military maneuvers, observed nuclear weapons tests, or provided technical support. At the Pacific Proving Ground (PPG), they served aboard ships or were stationed on islands during or after nuclear weapons tests. MATERIAL AND METHODS: Participants at seven test series, previously studied with high-quality dosimetry and personnel records, and the first test at TRINITY formed the cohort of 114,270 male military participants traced for vital status from 1945 through 2010. Dose reconstructions were based on Nuclear Test Personnel Review records, Department of Defense. Standardized mortality ratios (SMR) and Cox and Poisson regression models were used in the analysis. RESULTS: Most atomic veterans were enlisted men, served in the Navy at the PPG, and were born before 1930. Vital status was determined for 96.8% of the veterans; 60% had died. Enlisted men had significantly high all-causes mortality SMR (1.06); officers had significantly low all-causes mortality SMR (0.71). The pattern of risk over time showed a diminution of the 'healthy soldier effect': the all-causes mortality SMR after 50 years of follow-up was 1.00. The healthy soldier effect for all cancers also diminished over time. The all-cancer SMR was significantly high after 50 years (SMR 1.10) primarily from smoking-related cancers, attributed in part to the availability of cigarettes in military rations. The highest SMR was for mesothelioma (SMR 1.56) which was correlated with asbestos exposure in naval ships. Prostate cancer was significantly high (SMR 1.13). Ischemic heart disease was significantly low (SMR 0.84). Estimated mean doses varied by organ were low; e.g., the mean red bone marrow dose was 6 mGy (maximum 108 mGy). Internal cohort dose-response analyses provided no evidence for increasing trends with radiation dose for leukemia (excluding chronic lymphocytic leukemia (CLL)) [ERR (95% CI) per 100 mGy -0.37 (-1.08, 0.33); n = 710], CLL, myelodysplastic syndrome, multiple myeloma, ischemic heart disease, or cancers of the lung, prostate, breast, and brain. CONCLUSION: No statistically significant radiation associations were observed among 114,270 nuclear weapons test participants followed for up to 65 years. The 95% confidence limits were narrow and excluded mortality risks per unit dose that are two to four times higher than those reported in other investigations. Significantly elevated SMRs were seen for mesothelioma and asbestosis, attributed to asbestos exposure aboard ships.

Accounting for Unfissioned Plutonium from the Trinity Atomic Bomb Test.

The Trinity test device contained about 6 kg of plutonium as its fission source, resulting in a fission yield of 21 kT. However, only about 15% of the Pu actually underwent fission. The remaining unfissioned plutonium eventually was vaporized in the fireball and after cooling, was deposited downwind from the test site along with the various fission and activation products produced in the explosion. Using data from radiochemical analyses of soil samples collected postshot (most many years later), supplemented by model estimates of plutonium deposition density estimated from reported exposure rates at 12 h postshot, we have estimated the total activity and geographical distribution of the deposition density of this unfissioned plutonium in New Mexico. A majority (about 80%) of the unfissioned plutonium was deposited within the state of New Mexico, most in a relatively small area about 30-100 km downwind (the Chupadera Mesa area). For most of the state, the deposition density was a small fraction of the subsequent deposition density of Pu from Nevada Test Site tests (1951-1958) and later from global fallout from the large US and Russian thermonuclear tests (1952-1962). The fraction of the total unfissioned Pu that was deposited in New Mexico from Trinity was greater than the fraction of fission products deposited. Due to plutonium being highly refractory, a greater fraction of the Pu was incorporated into large particles that fell out closer to the test site as opposed to more volatile fission products (such as Cs and I) that tend to deposit on the surface of smaller particles that travel farther before depositing. The plutonium deposited as a result of the Trinity test was unlikely to have resulted in significant health risks to the downwind population.

Estimated Radiation Doses Received by New Mexico Residents from the 1945 Trinity Nuclear Test.

The National Cancer Institute study of projected health risks to New Mexico residents from the 1945 Trinity nuclear test provides best estimates of organ radiation absorbed doses received by representative persons according to ethnicity, age, and county. Doses to five organs/tissues at significant risk from exposure to radioactive fallout (i.e., active bone marrow, thyroid gland, lungs, stomach, and colon) from the 63 most important radionuclides in fresh fallout from external and internal irradiation were estimated. The organ doses were estimated for four resident ethnic groups in New Mexico (Whites, Hispanics, Native Americans, and African Americans) in seven age groups using: (1) assessment models described in a companion paper, (2) data on the spatial distribution and magnitude of radioactive fallout derived from historical documents, and (3) data collected on diets and lifestyles in 1945 from interviews and focus groups conducted in 2015-2017 (described in a companion paper). The organ doses were found to vary widely across the state with the highest doses directly to the northeast of the detonation site and at locations close to the center of the Trinity fallout plume. Spatial heterogeneity of fallout deposition was the largest cause of variation of doses across the state with lesser differences due to age and ethnicity, the latter because of differences in diets and lifestyles. The exposure pathways considered included both external irradiation from deposited fallout and internal irradiation via inhalation of airborne radionuclides in the debris cloud as well as resuspended ground activity and ingestion of contaminated drinking water (derived both from rivers and rainwater cisterns) and foodstuffs including milk products, beef, mutton, and pork, human-consumed plant products including leafy vegetables, fruit vegetables, fruits, and berries. Tables of best estimates of county population-weighted average organ doses by ethnicity and age are presented. A discussion of our estimates of uncertainty is also provided to illustrate a lower and upper credible range on our best estimates of doses. Our findings indicate that only small geographic areas immediately downwind to the northeast received exposures of any significance as judged by their magnitude relative to natural radiation. The findings presented are the most comprehensive and well-described estimates of doses received by populations of New Mexico from the Trinity nuclear test.

The Methodology Used to Assess Doses from the First Nuclear Weapons Test (Trinity) to the Populations of New Mexico.

Trinity was the first test of a nuclear fission device. The test took place in south-central New Mexico at the Alamogordo Bombing and Gunnery Range at 05:29 AM on 16 July 1945. This article provides detailed information on the methods that were used in this work to estimate the radiation doses that were received by the population that resided in New Mexico in 1945. The 721 voting precincts of New Mexico were classified according to ecozone (plains, mountains, or mixture of plains and mountains), and size of resident population (urban or rural). Methods were developed to prepare estimates of absorbed doses from a range of 63 radionuclides to five organs or tissues (thyroid, active marrow, stomach, colon, and lung) for representative individuals of each voting precinct selected according to ethnicity (Hispanic, White, Native American, and African American) and age group in 1945 (in utero, newborn, 1-2 y, 3-7 y, 8-12 y, 13-17 y, and adult). Three pathways of human exposure were included: (1) external irradiation from the radionuclides deposited on the ground; (2) inhalation of radionuclide-contaminated air during the passage of the radioactive cloud and, thereafter, of radionuclides transferred (resuspended) from soil to air; and (3) ingestion of contaminated water and foodstuffs. Within the ingestion pathway, 13 types of foods and sources of water were considered. Well established models were used for estimation of doses resulting from the three pathways using parameter values developed from extensive literature review. Because previous experience and calculations have shown that the annual dose delivered during the year following a nuclear test is much greater than the doses received in the years after that first year, the time period that was considered is limited to the first year following the day of the test (16 July 1945). Numerical estimates of absorbed doses, based on the methods described in this article, are presented in a separate article in this issue.

Estimation of Radiation Doses to U.S. Military Test Participants from Nuclear Testing: A Comparison of Historical Film-Badge Measurements, Dose Reconstruction and Retrospective Biodosimetry.

Retrospective radiation dose estimations, whether based on physical or biological measurements, or on theoretical dose reconstruction, are limited in their precision and reliability, particularly for exposures that occurred many decades ago. Here, we studied living U.S. military test participants, believed to have received high-dose radiation exposures during nuclear testing-related activities approximately six decades ago, with two primary goals in mind. The first was to compare three different approaches of assessing past radiation exposures: 1. Historical personnel monitoring data alone; 2. Dose reconstruction based on varying levels of completeness of individual information, which can include film badge data; and 3. Retrospective biodosimetry using chromosome aberrations in peripheral blood lymphocytes. The second goal was to use the collected data to make the best possible estimates of bone marrow dose received by a group with the highest military recorded radiation doses of any currently living military test participants. Six nuclear test participants studied had been on Rongerik Atoll during the 1954 CASTLE Bravo nuclear test. Another six were present at the Nevada Test Site (NTS) and/or Pacific Proving Ground (PPG) and were believed to have received relatively high-dose exposures at those locations. All were interviewed, and all provided a blood sample for cytogenetic analysis. Military dose records for each test participant, as recorded in the Defense Threat Reduction Agency's Nuclear Test Review and Information System, were used as the basis for historical film badge records and provided exposure scenario information to estimate dose via dose reconstruction. Dose to bone marrow was also estimated utilizing directional genomic hybridization (dGH) for high-resolution detection of radiation-induced chromosomal translocations and inversions, the latter being demonstrated for the first time for the purpose of retrospective biodosimetry. As the true dose for each test participant is not known these many decades after exposure, this study gauged the congruence of different methods by assessing the degree of correlation and degree of systematic differences. Overall, the best agreement between methods, defined by statistically significant correlations and small systematic differences, was between doses estimated by a dose reconstruction methodology that exploited all the available individual detail and the biodosimetry methodology derived from a weighted average dose determined from chromosomal translocation and inversion rates. Employing such a strategy, we found that the Rongerik veterans who participated in this study appear to have received, on average, bone marrow equivalent doses on the order of 300-400 mSv, while the NTS/ PPG participants appear to have received approximately 250-300 mSv. The results show that even for nuclear events that occurred six decades in the past, biological signatures of exposure are still present, and when taken together, chromosomal translocations and inversions can serve as reliable retrospective biodosimeters, particularly on a group-average basis, when doses received are greater than statistically-determined detection limits for the biological assays used.

Recent Epidemiologic Studies and the Linear No-Threshold Model For Radiation Protection-Considerations Regarding NCRP Commentary 27.

National Council on Radiation Protection and Measurements Commentary 27 examines recent epidemiologic data primarily from low-dose or low dose-rate studies of low linear-energy-transfer radiation and cancer to assess whether they support the linear no-threshold model as used in radiation protection. The commentary provides a critical review of low-dose or low dose-rate studies, most published within the last 10 y, that are applicable to current occupational, environmental, and medical radiation exposures. The strengths and weaknesses of the epidemiologic methods, dosimetry assessments, and statistical modeling of 29 epidemiologic studies of total solid cancer, leukemia, breast cancer, and thyroid cancer, as well as heritable effects and a few nonmalignant conditions, were evaluated. An appraisal of the degree to which the low-dose or low dose-rate studies supported a linear no-threshold model for radiation protection or on the contrary, demonstrated sufficient evidence that the linear no-threshold model is inappropriate for the purposes of radiation protection was also included. The review found that many, though not all, studies of solid cancer supported the continued use of the linear no-threshold model in radiation protection. Evaluations of the principal studies of leukemia and low-dose or low dose-rate radiation exposure also lent support for the linear no-threshold model as used in protection. Ischemic heart disease, a major type of cardiovascular disease, was examined briefly, but the results of recent studies were considered too weak or inconsistent to allow firm conclusions regarding support of the linear no-threshold model. It is acknowledged that the possible risks from very low doses of low linear-energy-transfer radiation are small and uncertain and that it may never be possible to prove or disprove the validity of the linear no-threshold assumption by epidemiologic means. Nonetheless, the preponderance of recent epidemiologic data on solid cancer is supportive of the continued use of the linear no-threshold model for the purposes of radiation protection. This conclusion is in accord with judgments by other national and international scientific committees, based on somewhat older data. Currently, no alternative dose-response relationship appears more pragmatic or prudent for radiation protection purposes than the linear no-threshold model.

A review of dosimetry used in epidemiological studies considered to evaluate the linear no-threshold (LNT) dose-response model for radiation protection.

BACKGROUND: Accurate dosimetry is key to deriving the dose response from radiation exposure in an epidemiological study. It becomes increasingly important to estimate dose as accurately as possible when evaluating low dose and low dose rate as the calculation of excess relative risk per Gray (ERR/Gy) is very sensitive to the number of excess cancers observed, and this can lead to significant errors if the dosimetry is of poor quality. By including an analysis of the dosimetry, we gain a far better appreciation of the robustness of the work from the standpoint of its value in supporting the shape of the dose response curve at low doses and low dose rates. This article summarizes a review of dosimetry supporting epidemiological studies currently being considered for a re-evaluation of the linear no-threshold assumption as a basis for radiation protection. The dosimetry for each study was evaluated based on important attributes from a dosimetry perspective. Our dosimetry review consisted of dosimetry supporting epidemiological studies published in the literature during the past 15 years. Based on our review, it is clear there is wide variation in the quality of the dosimetry underlying each study. Every study has strengths and weaknesses. The article describes the results of our review, explaining which studies clearly stand out for their strengths as well as common weaknesses among all investigations. PURPOSE: To summarize a review of dosimetry used in epidemiological studies being considered by the National Council on Radiation Protection and Measurements (NCRP) in an evaluation of the linear no-threshold dose-response model that underpins the current framework of radiation protection. MATERIALS AND METHODS: The authors evaluated each study using criteria considered important from a dosimetry perspective. The dosimetry analysis was divided into the following categories: (1) general study characteristics, (2) dose assignment, (3) uncertainty, (4) dose confounders (5) dose validation, and (6) strengths and weaknesses of the dosimetry. Our review focused on approximately 20 studies published in the literature primarily during the past 15 years. RESULTS: Based on the review, it is clear there is wide variation in the quality of the dosimetry underlying each study. Every study has strengths and weaknesses. This paper describes the results of our review, identifies common weaknesses among all investigations, and recognizes studies that clearly stand out for their overall strengths. CONCLUSIONS: The paper concludes by offering recommendations to investigators on possible ways in which dosimetry could be improved in future epidemiological studies.

Red Bone Marrow and Male Breast Doses for a Cohort of Atomic Veterans.

Both red bone marrow and male breast doses with associated uncertainty have been reconstructed for a 1,982-person subset of a cohort of 114, 270 military personnel (referred to as "atomic veterans") who participated in U.S. atmospheric nuclear weapons testing from 1945 to 1962. The methods used to calculate these doses and corresponding uncertainty have been reported in detail by Till et al. in an earlier publication. In this current article we report the final results of those calculations. These doses are being used in a case-cohort design epidemiological investigation of leukemia and male breast cancer. This cohort of atomic veterans is one component in a broader-scope study of approximately one million U.S. persons designed to investigate risk from chronic low-dose radiation exposure. Doses to the atomic veterans in this sub-cohort were relatively low, with approximately two-thirds receiving red bone marrow doses <5 mGy and only four individuals receiving a red bone marrow dose >50 mGy. The average red bone marrow dose for members of the sub-cohort was 5.9 mGy. Doses to male breast were approximately 20% higher than red bone marrow doses. The uncertainty in the estimated doses was relatively low, considering relevant personnel dosimetry was available for only about 25% of the subjects, and most of the doses were reconstructed from film badges worn by co-workers or from the individual's military record and military unit activities. The average coefficient of variation for the individual dose estimates was approximately 0.5, comparable to the uncertainty in doses estimated for the Japanese A-bomb survivors. Although the reconstructed red bone marrow doses were about 36% lower on average than the conservative doses previously estimated by the military for compensation, the overall correlation was quite good, suggesting that the estimates of doses from external exposure by the military for all ∼115,000 cohort members could be adjusted appropriately and used in further epidemiological analyses.

Workshop Report on Atomic Bomb Dosimetry--Review of Dose Related Factors for the Evaluation of Exposures to Residual Radiation at Hiroshima and Nagasaki.

Groups of Japanese and American scientists, supported by international collaborators, have worked for many years to ensure the accuracy of the radiation dosimetry used in studies of health effects in the Japanese atomic bomb survivors. Reliable dosimetric models and systems are especially critical to epidemiologic studies of this population because of their importance in the development of worldwide radiation protection standards. While dosimetry systems, such as Dosimetry System 1986 (DS86) and Dosimetry System 2002 (DS02), have improved, the research groups that developed them were unable to propose or confirm an additional contribution by residual radiation to the survivor's total body dose. In recognition of the need for an up-to-date review of residual radiation exposures in Hiroshima and Nagasaki, a half-day technical session was held for reports on newer studies at the 59 th Annual HPS Meeting in 2014 in Baltimore, MD. A day-and-a-half workshop was also held to provide time for detailed discussion of the newer studies and to evaluate their potential use in clarifying the residual radiation exposure to atomic bomb survivors at Hiroshima and Nagasaki. The process also involved a re-examination of very early surveys of radioisotope emissions from ground surfaces at Hiroshima and Nagasaki and early reports of health effects. New insights were reported on the potential contribution to residual radiation from neutron-activated radionuclides in the airburst's dust stem and pedestal and in unlofted soil, as well as from fission products and weapon debris from the nuclear cloud. However, disparate views remain concerning the actual residual radiation doses received by the atomic bomb survivors at different distances from the hypocenter. The workshop discussion indicated that measurements made using thermal luminescence and optically stimulated luminescence, like earlier measurements, especially in very thin layers of the samples, could be expanded to detect possible radiation exposures to beta particles and to determine their significance plus the extent of the various residual radiation areas at Hiroshima and Nagasaki. Other suggestions for future residual radiation studies are included in this workshop report.

Dose reconstruction for the million worker study: status and guidelines.

The primary aim of the epidemiologic study of one million U.S. radiation workers and veterans [the Million Worker Study (MWS)] is to provide scientifically valid information on the level of radiation risk when exposures are received gradually over time and not within seconds, as was the case for Japanese atomic bomb survivors. The primary outcome of the epidemiologic study is cancer mortality, but other causes of death such as cardiovascular disease and cerebrovascular disease will be evaluated. The success of the study is tied to the validity of the dose reconstruction approaches to provide realistic estimates of organ-specific radiation absorbed doses that are as accurate and precise as possible and to properly evaluate their accompanying uncertainties. The dosimetry aspects for the MWS are challenging in that they address diverse exposure scenarios for diverse occupational groups being studied over a period of up to 70 y. The dosimetric issues differ among the varied exposed populations that are considered: atomic veterans, U.S. Department of Energy workers exposed to both penetrating radiation and intakes of radionuclides, nuclear power plant workers, medical radiation workers, and industrial radiographers. While a major source of radiation exposure to the study population comes from external gamma- or x-ray sources, for some of the study groups, there is a meaningful component of radionuclide intakes that requires internal radiation dosimetry assessments. Scientific Committee 6-9 has been established by the National Council on Radiation Protection and Measurements (NCRP) to produce a report on the comprehensive organ dose assessment (including uncertainty analysis) for the MWS. The NCRP dosimetry report will cover the specifics of practical dose reconstruction for the ongoing epidemiologic studies with uncertainty analysis discussions and will be a specific application of the guidance provided in NCRP Report Nos. 158, 163, 164, and 171. The main role of the Committee is to provide guidelines to the various groups of dosimetrists involved in the MWS to ensure that certain dosimetry criteria are considered: calculation of annual absorbed doses in the organs of interest, separation of low and high linear-energy transfer components, evaluation of uncertainties, and quality assurance and quality control. It is recognized that the MWS and its approaches to dosimetry are a work in progress and that there will be flexibility and changes in direction as new information is obtained with regard to both dosimetry and the epidemiologic features of the study components. This paper focuses on the description of the various components of the MWS, the available dosimetry results, and the challenges that have been encountered. It is expected that the Committee will complete its report in 2016.