The Million Person Study, whence it came and why

AT, Raavi V, Easwaramoorthy V, Murugaiyan P, Perumal V. Enhanced γ-H2AX Foci Frequency and Altered Gene Expression in Participants Exposed to Ionizing Radiation During I-131 Nuclear Medicine Procedures

Purpose

Ionizing radiation-based technologies are extensively used in the diagnosis and treatment of diseases. While utilizing the technologies, exposure to a certain amount of radiation is unavoidable. Data can be obtained from participants who received radiation during medical imaging and therapeutic purposes to predict the effects of low-dose radiation.

Methods

To understand the effects of low-dose radiation, participants (n = 22) who received radioactive I-131 for scan/therapy were used as a model in this study. Blood samples were drawn pre- and post-administration of I-131. Biological effects were measured using markers of DNA damage (γ-H2AX, micronucleus (MN), and chromosomal aberrations (CA)) and response to damage through gene expression changes (ATM, CDKN1A, DDB2, FDXR, and PCNA) in blood samples.

Results

Mean frequency of γ-H2AX foci in pre-samples was 0.28 ± 0.16, and post-samples were 1.03 ± 0.60. γ-H2AX foci frequency obtained from post-samples showed significant (p < 0.0001) and a heterogeneous increase in all the participants (received I-131 for scan/therapy) when compared to pre-samples. A significant increase (p < 0.0001) in MN and CA frequency was also observed in participants who received the I-131 therapy. Gene expression analysis indicates that all genes (ATM, CDKN1A, DDB2, FDXR, and PCNA) were altered in post-samples, although with varying degrees, suggesting that the cellular responses to DNA damage, such as damage repair, cell cycle regulation to aid in repair and apoptosis are increased, which priority is given to repair, followed by apoptosis.

Conclusion

The results of this study indicate that the participants who received I-131 (low doses of β- and γ-radiation) can produce substantial biological effects.

A Historical Survey of Key Epidemiological Studies of Ionizing Radiation Exposure

In this article we review the history of key epidemiological studies of populations exposed to ionizing radiation. We highlight historical and recent findings regarding radiation-associated risks for incidence and mortality of cancer and non-cancer outcomes with emphasis on study design and methods of exposure assessment and dose estimation along with brief consideration of sources of bias for a few of the more important studies. We examine the findings from the epidemiological studies of the Japanese atomic bomb survivors, persons exposed to radiation for diagnostic or therapeutic purposes, those exposed to environmental sources including Chornobyl and other reactor accidents, and occupationally exposed cohorts. We also summarize results of pooled studies. These summaries are necessarily brief, but we provide references to more detailed information. We discuss possible future directions of study, to include assessment of susceptible populations, and possible new populations, data sources, study designs and methods of analysis.

Adjustment for duration of employment in occupational epidemiology

PURPOSE

In occupational epidemiology, the healthy worker survivor effect can manifest as a time-dependent confounder because healthier workers can accrue greater amounts of exposure over longer periods of employment. For example, in occupational studies of radiation exposure that focus on cumulative annualized radiation dose, workers can accrue greater amounts of cumulative radiation exposure over longer periods of employment, while workers with longer periods of employment can transition into jobs with a reduced potential for annualized radiation exposure. The extent to which confounding arising from the healthy worker survivor effect impacts radiation risk estimates is unknown.

METHODS

We assessed the impact of the healthy worker survivor effect on estimates of radiation risk among nuclear workers in a Million Person Study cohort. In simulation studies, we contrasted the ability of marginal structural Cox models with inverse probability weighting and Cox proportional hazards models to account for time-dependent confounding arising from the healthy worker survivor effect.

RESULTS

Marginal structural Cox models and Cox proportional hazards models with flexible functional forms for duration of employment provided reliable results.

CONCLUSIONS

It is crucial to flexibly adjust for duration of employment to account for confounding arising from the healthy worker survivor effect in occupational epidemiology.

Evaluating county-level lung cancer incidence from environmental radiation exposure, PM2.5, and other exposures with regression and machine learning models

Characterizing the interplay between exposures shaping the human exposome is vital for uncovering the etiology of complex diseases. For example, cancer risk is modified by a range of multifactorial external environmental exposures. Environmental, socioeconomic, and lifestyle factors all shape lung cancer risk. However, epidemiological studies of radon aimed at identifying populations at high risk for lung cancer often fail to consider multiple exposures simultaneously. For example, moderating factors, such as PM2.5, may affect the transport of radon progeny to lung tissue. This ecological analysis leveraged a population-level dataset from the National Cancer Institute's Surveillance, Epidemiology, and End-Results data (2013-17) to simultaneously investigate the effect of multiple sources of low-dose radiation (gross [Formula: see text] activity and indoor radon) and PM2.5 on lung cancer incidence rates in the USA. County-level factors (environmental, sociodemographic, lifestyle) were controlled for, and Poisson regression and random forest models were used to assess the association between radon exposure and lung and bronchus cancer incidence rates. Tree-based machine learning (ML) method perform better than traditional regression: Poisson regression: 6.29/7.13 (mean absolute percentage error, MAPE), 12.70/12.77 (root mean square error, RMSE); Poisson random forest regression: 1.22/1.16 (MAPE), 8.01/8.15 (RMSE). The effect of PM2.5 increased with the concentration of environmental radon, thereby confirming findings from previous studies that investigated the possible synergistic effect of radon and PM2.5 on health outcomes. In summary, the results demonstrated (1) a need to consider multiple environmental exposures when assessing radon exposure's association with lung cancer risk, thereby highlighting (1) the importance of an exposomics framework and (2) that employing ML models may capture the complex interplay between environmental exposures and health, as in the case of indoor radon exposure and lung cancer incidence.

Moon, Mars and Minds: Evaluating Parkinson's disease mortality among U.S. radiation workers and veterans in the million person study of low-dose effects

BACKGROUND

Radiation is one of the most important stressors related to missions in space beyond Earth's orbit. Epidemiologic studies of exposed workers have reported elevated rates of Parkinson's disease. The importance of cognitive dysfunction related to low-dose rate radiation in humans is not defined. A meta-analysis was conducted of six cohorts in the Million Person Study (MPS) of low-dose health effects to learn whether there is consistent evidence that Parkinson's disease is associated with radiation dose to brain.

MATERIALS AND METHODS

The MPS evaluates all causes of death among U.S. radiation workers and veterans, including Parkinson's disease. Systematic and consistent methods are applied to study all categories of workers including medical radiation workers, industrial radiographers, nuclear power plant workers, atomic veterans, and Manhattan Projects workers at the Los Alamos National Laboratory and at Rocky Flats. Consistent methods for all cohorts are used to estimate organ-specific doses and to obtain vital status and cause of death.

RESULTS

The meta-analysis include 6 cohorts within the MPS, consisting of 517,608 workers and 17,219,001 person-years of observation. The mean dose to brain ranged from 6.9 to 47.6 mGy and the maximum dose from 0.76 to 2.7 Gy. Five of the 6 cohorts revealed positive associations with Parkinson's disease. The overall summary estimate from the meta-analysis was statistically significant based on 1573 deaths due to Parkinson's disease. The summary excess relative risk at 100 mGy was 0.17 (95% CI: 0.05; 0.29).

CONCLUSIONS

Parkinson's disease was positively associated with radiation in the MPS cohorts indicating the need for careful evaluation as to causality in other studies, delineation of possible mechanisms, and assessing possible implications for space travel as well as radiation protection guidance for terrestrial workers.

Third mortality follow-up of the Mallinckrodt uranium processing workers, 1942-2019

INTRODUCTION

Mallinckrodt Chemical Works was a uranium processing facility during the Manhattan Project from 1942 to 1966. Thousands of workers were exposed to low-dose-rates of ionizing radiation from external and internal sources. This third follow-up of 2514 White male employees updates cancer and noncancer mortality potentially associated with radiation and silica dust.

MATERIALS AND METHODS

Individual, annualized organ doses were estimated from film badge records (n monitored = 2514), occupational chest x-rays (n = 2514), uranium urinalysis (n = 1868), radium intake through radon breath measurements (n = 487), and radon ambient measurements (n = 1356). Silica dust exposure from pitchblende processing was estimated (n = 1317). Vital status and cause of death determination through 2019 relied upon the National Death Index and Social Security Administration Epidemiological Vital Status Service. The analysis included standardized mortality ratios (SMRs), Cox proportional hazards, and Poisson regression models.

RESULTS

Vital status was confirmed for 99.4% of workers (84.0% deceased). For a dose weighting factor of 1 for intakes of uranium, radium, and radon decay products, the mean and median lung doses were 65.6 and 29.9 mGy, respectively. SMRs indicated a difference in health outcomes between salaried and hourly workers, and more brain cancer deaths than expected [SMR: 1.79; 95% confidence interval (CI): 1.14, 2.70]. No association was seen between radiation and lung cancer [hazard ratio (HR) at 100 mGy: 0.93; 95%CI: 0.78, 1.11]. The relationship between radiation and kidney cancer observed in the previous follow-up was maintained (HR at 100 mGy: 2.07; 95%CI: 1.12, 3.79). Cardiovascular disease (CVD) also increased significantly with heart dose (HR at 100 mGy: 1.11; 95%CI: 1.02, 1.21). Exposures to dust ≥23.6 mg/m3-year were associated with nonmalignant kidney disease (NMKD) (HR: 3.02; 95%CI: 1.12, 8.16) and kidney cancer combined with NMKD (HR: 2.46; 95%CI: 1.04, 5.81), though without evidence of a dose-response per 100 mg/m3-year.

CONCLUSIONS

This third follow-up of Mallinckrodt uranium processors reinforced the results of the previous studies. There was an excess of brain cancers compared with the US population, although no radiation dose-response was detected. The association between radiation and kidney cancer remained, though potentially due to few cases at higher doses. The association between levels of silica dust ≥23.6 mg/m3-year and NMKD also remained. No association was observed between radiation and lung cancer. A positive dose-response was observed between radiation and CVD; however, this association may be confounded by smoking, which was unmeasured. Future work will pool these data with other uranium processing worker cohorts within the Million Person Study.

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.

How the Science of Radiation Biology Can Help Reduce the Crippling Fear of Low-level Radiation

ABSTRACT

The fear of radiation has been present almost since the discovery of radiation, but has intensified since the "dawn of the atomic age" over 75 y ago. This fear has often served as an impediment to the safe and beneficial uses of radiation and radioactive material. The underlying causes of such fear are varied, can be complex, and are often not associated with any scientific knowledge or understanding. The authors believe that a clear understanding of the current scientific knowledge and understanding of the effects of radiation exposure may be useful in helping to allay some of the fear of radiation. This manuscript attempts to (1) address several scientific questions that we believe have contributed to the fear of radiation, (2) review the data derived from research that can be used to address these questions, and (3) summarize how the results of such scientific research can be used to help address the fear of low-dose and low-dose-rate radiation. Several examples of how fear of radiation has affected public perception of radiological events are discussed, as well as a brief history of the etiology of radiation fear. Actions needed to reduce the public fear of radiation and help fulfill the full societal benefits of radiation and radioactive materials are suggested.

Exposure to Ionizing Radiation and Risk of Dementia: A Systematic Review and Meta-Analysis

The number of people living with dementia is rising globally as life expectancy increases. Dementia is a multifactorial disease. Due to the ubiquity of radiation exposure in medical and occupational settings, the potential association between radiation and dementia, and its subtypes (Alzheimer's and Parkinson's disease), is of particular importance. There has also been an increased interest in studying radiation induced dementia risks in connection with the long-term manned space travel proposed by The National Aeronautics and Space Administration (NASA). Our aim was to systematically review the literature on this topic, and use meta-analysis to generate a summary measure of association, assess publication bias and explore sources of heterogeneity across studies. We identified five types of exposed populations for this review: 1. survivors of atomic bombings in Japan; 2. patients treated with radiation therapy for cancer or other diseases; 3. occupationally exposed workers; 4. those exposed to environmental radiation; and 5. patients exposed to radiation from diagnostic radiation imaging procedures. We included studies that considered incident or mortality outcomes for dementia and its subtypes. Following PRISMA guidelines, we systematically searched the published literature indexed in PubMed between 2001 and 2022. We then abstracted the relevant articles, conducted a risk-of-bias assessment, and fit random effects models using the published risk estimates. After we applied our eligibility criteria, 18 studies were identified for review and retained for meta-analysis. For dementia (all subtypes), the summary relative risk was 1.11 (95% CI: 1.04, 1.18; P = 0.001) comparing individuals receiving 100 mSv of radiation to those with no exposure. The corresponding summary relative risk for Parkinson's disease incidence and mortality was 1.12 (95% CI 1.07, 1.17; P <0.001). Our results provide evidence that exposure to ionizing radiation increases the risk of dementia. However, our findings should be interpreted with caution due to the small number of included studies. Longitudinal studies with improved exposure characterization, incident outcomes, larger sample size, and the ability to adjust for effects of potential confounders are needed to better assess the possible causal link between ionizing radiation and dementia.

Mortality among Tennessee Eastman Corporation (TEC) uranium processing workers, 1943-2019

BACKGROUND

There are few occupational studies of women exposed to ionizing radiation. During World War II, the Tennessee Eastman Corporation (TEC) operated an electromagnetic field separation facility of 1152 calutrons to obtain enriched uranium (²³⁵U) used for the Hiroshima atomic bomb. Thousands of women were involved in these operations.

MATERIALS AND METHODS

A new study was conducted of 13,951 women and 12,699 men employed at TEC between 1943 and 1947 for at least 90 days. Comprehensive dose reconstruction techniques were used to estimate lung doses from the inhalation of uranium dust based on airborne measurements. Vital status through 2018/2019 was obtained from the National Death Index, Social Security Death Index, Tennessee death records and online public record databases. Analyses included standardized mortality ratios (SMRs) and Cox proportional hazards models.

RESULTS

Most workers were hourly (77.7%), white (95.6%), born before 1920 (58.3%), worked in dusty environments (57.0%), and had died (94.9%). Vital status was confirmed for 97.4% of the workers. Women were younger than men when first employed: mean ages 25.0 years and 33.0 years, respectively. The estimated mean absorbed dose to the lung was 32.7 mGy (max 1048 mGy) for women and 18.9 mGy (max 501 mGy) for men. The mean dose to thoracic lymph nodes (TLNs) was 127 mGy. Statistically significant SMRs were observed for lung cancer (SMR 1.25; 95% CI 1.19, 1.31; n = 1654), nonmalignant respiratory diseases (NMRDs) (1.23; 95% CI 1.19, 1.28; n = 2585), and cerebrovascular disease (CeVD) (1.13; 95% CI 1.08, 1.18; n = 1945). For lung cancer, the excess relative rate (ERR) at 100 mGy (95% CI) was 0.01 (-0.10, 0.12; n = 652) among women, and -0.15 (-0.38, 0.07; n = 1002) among men based on a preferred model for men with lung doses <300 mGy. NMRD and non-Hodgkin lymphoma were not associated with estimated absorbed dose to the lung or TLN.

CONCLUSIONS

There was little evidence that radiation increased the risk of lung cancer, suggesting that inhalation of uranium dust and the associated high-LET alpha particle exposure to lung tissue experienced over a few years is less effective in causing lung cancer than other types of exposures. There was no statistically significant difference in the lung cancer risk estimates between men and women. The elevation of certain causes of death such as CeVD is unexplained and will require additional scrutiny of workplace or lifestyle factors given that radiation is an unlikely contributor since only the lung and lymph nodes received appreciable dose.

Mortality among medical radiation workers in the United States, 1965-2016

BACKGROUND

Estimates of radiation risks following prolonged exposures at low doses and low-dose rates are uncertain. Medical radiation workers are a major component of the Million Person Study (MPS) of low-dose health effects. Annual personal dose equivalents, H_P(10), for individual workers are available to facilitate dose-response analyses for lung cancer, leukemia, ischemic heart disease (IHD) and other causes of death.

MATERIALS AND METHODS

The Landauer, Inc. dosimetry database identified 109,019 medical and associated radiation workers first monitored 1965-1994. Vital status and cause of death were determined through 2016. Mean absorbed doses to red bone marrow (RBM), lung, heart, and other organs were estimated by adjusting the recorded H_P(10) for each worker by scaling factors, accounting for exposure geometry, the energy of the incident photon radiation, sex of the worker and whether an apron was worn. There were 4 exposure scenarios: general radiology characterized by low-energy x-ray exposure with no lead apron use, interventional radiologists/cardiologists who wore aprons, nuclear medicine personnel and radiation oncologists exposed to high-energy photon radiation, and other workers. Standardized mortality ratio (SMR) analyses were performed. Cox proportional hazards models were used to estimate organ-specific radiation risks.

RESULTS

Overall, 11,433 deaths occurred (SMR 0.60; 95%CI 0.59,0.61), 126 from leukemia other than chronic lymphocytic leukemia (CLL), 850 from lung cancer, and 1654 from IHD. The mean duration of monitoring was 23.7 y. The excess relative rate (ERR) per 100 mGy was estimated as 0.10 (95% CI -0.34, 0.54) for leukemia other than CLL, 0.15 (0.02, 0.27) for lung cancer, and -0.10 (-0.27, 0.06) for IHD. The ERR for lung cancer was 0.16 (0.01, 0.32) among the 55,218 male workers and 0.09 (-0.19, 0.36) among the 53,801 female workers; a difference that was not statistically significant (p-value = 0.23).

CONCLUSIONS

Medical radiation workers were at increased risk for lung cancer that was higher among men than women, although this difference was not statistically significant. In contrast, the study of Japanese atomic bomb survivors exposed briefly to radiation in 1945 found females to be nearly 3 times the radiation risk of lung cancer compared with males on a relative scale. For medical workers, there were no statistically significant radiation associations with leukemia excluding CLL, IHD or other specific causes of death. Combining these data with other cohorts within the MPS, such as nuclear power plant workers and nuclear submariners, will enable more precise estimates of radiation risks at relatively low cumulative doses.

Summary of Radiation Research Society Online 67th Annual Meeting, Symposium on "Radiation and Circulatory Effects"

PURPOSE

This article summarizes a number of presentations from a session on "Radiation and Circulatory Effects" held during the Radiation Research Society Online 67^th Annual Meeting, October 3-6 2021.

MATERIALS AND METHODS

Different epidemiological cohorts were analyzed with various statistical means common in epidemiology. The cohorts included the one from the U.S. Million Person Study and the Canadian Fluoroscopy Cohort Study. In addition, one of the contributions in our article relies on results from analyses of the Japanese atomic bomb survivors, Russian emergency and recovery workers and cohorts of nuclear workers. The Canadian Fluoroscopy Cohort Study data were analyzed with a larger series of linear and nonlinear dose-response models in addition to the linear no-threshold (LNT) model.

RESULTS AND CONCLUSIONS

The talks in this symposium showed that low/moderate acute doses at low/moderate dose rates can be associated with an increased risk of CVD, although some of the epidemiological results for occupational cohorts are equivocal. The usually only limited availability of information on well-known risk factors for circulatory disease (e.g. smoking, obesity, hypertension, diabetes, physical activity) is an important limiting factor that may bias any observed association between radiation exposure and detrimental health outcome, especially at low doses. Additional follow-up and careful dosimetric and outcome assessment are necessary and more epidemiological and experimental research is required. Obtaining reliable information on other risk factors is especially important.

Updated Mortality Analysis of SELTINE, the French Cohort of Nuclear Workers, 1968-2014

Cohorts of nuclear workers are particularly relevant to study the health effects of protracted exposures to low doses at low dose-rates of ionizing radiation (IR). In France, a cohort of nuclear workers badge-monitored for external IR exposure has been followed-up for several decades. Its size and follow-up period have recently been extended. The present paper focuses on mortality from both cancer and non-cancer diseases in this cohort. The SELTINE cohort of nuclear workers employed by CEA, Orano, and EDF companies was followed-up for mortality from 1968 to 2014. Mortality in the cohort was compared to that in the French general population. Poisson regression methods were used to estimate excess relative rates of mortality per unit of cumulative dose of IR, adjusted for calendar year, age, company, duration of employment, and socioeconomic status. The cohort included 80,348 workers. At the end of the follow-up, the mean attained age was 63 years, and 15,695 deaths were observed. A strong healthy worker effect was observed overall. A significant excess of pleural cancer mortality was observed but not associated with IR dose. Death from solid cancers was positively but non-significantly associated with radiation. Death from leukaemia (excluding chronic lymphocytic leukaemia), dementia, and Alzheimer's disease were positively and significantly associated with IR dose. Estimated dose-risk relationships were consistent with those from other nuclear worker studies for all solid cancers and leukaemia but remained associated with large uncertainty. The association between IR dose and dementia mortality risk should be interpreted with caution and requires further investigation by other studies.

Radiation and CNS effects: summary of evidence from a recent symposium of the Radiation Research Society

This article summarizes a Symposium on 'Radiation risks of the central nervous system' held virtually at the 67th Annual Meeting of the Radiation Research Society, 3-6 October 2021. Repeated low-dose radiation exposure over a certain period could lead to reduced neuronal proliferation, altered neurogenesis, neuroinflammation and various neurological complications, including psychological consequences, necessitating further research in these areas. Four speakers from radiation biology, genetics and epidemiology presented the latest data from their studies seeking insights into this important topic. This symposium highlighted new and important directions for further research on mental health disorders, neurodegenerative conditions and cognitive impairment. Future studies will examine risks of mental and behavioral disorders and neurodegenerative diseases following protracted radiation exposures to better understand risks of occupational exposures as well as provide insights into risks from exposures to galactic cosmic rays.

Low Dose and Non-Targeted Radiation Effects in Environmental Protection and Medicine-A New Model Focusing on Electromagnetic Signaling

The role of signalling in initiating and perpetuating effects triggered by deposition of ionising radiation energy in parts of a system is very clear. Less clear are the very early steps involved in converting energy to chemical and biological effects in non-targeted parts of the system. The paper aims to present a new model, which could aid our understanding of the role of low dose effects in determining ultimate disease outcomes. We propose a key role for electromagnetic signals resulting from physico-chemical processes such as excitation decay, and acoustic waves. These lead to the initiation of damage response pathways such as elevation of reactive oxygen species and membrane associated changes in key ion channels. Critically, these signalling pathways allow coordination of responses across system levels. For example, depending on how these perturbations are transduced, adverse or beneficial outcomes may predominate. We suggest that by appreciating the importance of signalling and communication between multiple levels of organisation, a unified theory could emerge. This would allow the development of models incorporating time, space and system level to position data in appropriate areas of a multidimensional domain. We propose the use of the term "infosome" to capture the nature of radiation-induced communication systems which include physical as well as chemical signals. We have named our model "the variable response model" or "VRM" which allows for multiple outcomes following exposure to low doses or to signals from low dose irradiated cells, tissues or organisms. We suggest that the use of both dose and infosome in radiation protection might open up new conceptual avenues that could allow intrinsic uncertainty to be embraced within a holistic protection framework.

International expert group collaboration for developing an adverse outcome pathway for radiation induced leukaemia

PURPOSE

The concept of the adverse outcome pathway (AOP) has recently gained significant attention as to its potential for incorporation of mechanistic biological information into the assessment of adverse health outcomes following ionizing radiation (IR) exposure. This work is an account of the activities of an international expert group formed specifically to develop an AOP for IR-induced leukaemia. Group discussions were held during dedicated sessions at the international AOP workshop jointly organized by the MELODI (Multidisciplinary European Low Dose Initiative) and the ALLIANCE (European Radioecology Alliance) associations to consolidate knowledge into a number of biological key events causally linked by key event relationships and connecting a molecular initiating event with the adverse outcome. Further knowledge review to generate a weight of evidence support for the Key Event Relationships (KERs) was undertaken using a systematic review approach.

CONCLUSIONS

An AOP for IR-induced acute myeloid leukaemia was proposed and submitted for review to the OECD-curated AOP-wiki (aopwiki.org). The systematic review identified over 500 studies that link IR, as a stressor, to leukaemia, as an adverse outcome. Knowledge gap identification, although requiring a substantial effort via systematic review of literature, appears to be one of the major added values of the AOP concept. Further work, both within this leukaemia AOP working group and other similar working groups, is warranted and is anticipated to produce highly demanded products for the radiation protection research community.

Methods of improving brain dose estimates for internally deposited radionuclides. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2022;42:033001. [PMID: 35785774 DOI: 10.1088/1361-6498/ac7e02]

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.

The Improvement of the Regional Regulatory Governance System for Radiation Risk Management: Spatial Analysis on Radiation Hazards in South Korea

Since the 2011 Fukushima nuclear power plant accident, nuclear regulators have strengthened safety standards or decided to decommission the nuclear power plant. The vast majority of radiation is from nuclear power plants, so safety measures are also concentrated in nuclear power plants. Radioactive materials located much closer to the people are scattered around the nation. However, it is difficult for citizens to predict the radiation risk around them because regulatory agencies do not provide adequate information on radiation. The main goal of this study is to analyze the spatial distribution patterns of radioactive materials that serve as indicators for potential risk from a radiological hazard. The empirical findings in this study demonstrate the presence of spatial autocorrelation for the number of radiation licenses among 244 regions in the Republic of Korea. The policy implications are three-fold: (1) it is necessary to improve regulatory governance in consideration of permitted use; (2) the regional offices of regulatory agency can be established based on the identified spatial distribution of permitted use; (3) it is required to improve the information-disclosure system for materials. This study provides an opportunity to create a safer society by understanding the radiation around the public in general.

A brief overview of the registration system of radiation exposure doses for decontamination workers and their occupational health management

Following the Fukushima nuclear accident in March 2011, decontamination and related works have been carried out over a wide area, mainly in Fukushima Prefecture. In November 2013, the Radiation Dose Registration and Management System for Decontamination Workers was established to manage the occupational exposure doses of workers engaged in such work. The Radiation Effects Association mainly operates the registration system. This paper summarizes existing reports on this system and occupational health issues among decontamination workers. We collected previous reports and related regulatory laws on occupational health management for decontamination workers working in Fukushima Prefecture, summarized the outline of the radiation dose registration and management system for these decontamination workers, and discussed future issues related to their health management. Approximately 100 000 decontamination workers were registered in the system as of 2020, but none showed radiation doses that exceeded the dose limit. To our knowledge, there have been no reports of decontamination workers presenting physical symptoms suspected to be related to radiation exposure. On the other hand, heatstroke countermeasures and anxiety about radiation exposure have been reported as possible issues in the occupational health management of decontamination workers. Although decontamination workers are unlikely to experience biological effects from radiation exposure, epidemiological studies are needed to examine this evidence. Further analysis is also needed on non-radiation effects, which pose occupational health concerns for decontamination workers. The registration system would allow for tracking decontamination workers, providing data for analyzing radiological and non-radiological effects.

Overview of epidemiological studies of nuclear workers: opportunities, expectations, and limitations. JOURNAL OF RADIOLOGICAL PROTECTION : OFFICIAL JOURNAL OF THE SOCIETY FOR RADIOLOGICAL PROTECTION 2021;41:1075-1092. [PMID: 34161930 DOI: 10.1088/1361-6498/ac0df4]

Epidemiological studies of those exposed occupationally to ionising radiation offer an important opportunity to directly check the assumptions underlying the international system of radiological protection against low-level radiation exposures. Recent nuclear worker studies, notably the International Nuclear Workers Study (INWORKS) and studies of the Mayak workforce in Russia, provide powerful investigations of a wide range of cumulative photon doses received at a low dose-rate over protracted periods, and broadly confirm radiation-related excess risks of leukaemia and solid cancers at around the levels predicted by standard risk models derived mainly from the experience of the Japanese atomic-bomb survivors acutely exposed principally to gamma radiation. However, the slope of the dose-response for solid cancers expressed in terms of the excess relative risk per unit dose, ERR/Gy, differs between INWORKS and Mayak, such that when compared with the slope derived from the atomic-bomb survivors, INWORKS does not provide obvious support for the use in radiological protection of a dose and dose-rate effectiveness factor greater than one whereas the Mayak workforce apparently does. This difference could be a chance effect, but it could also point to potential problems with these worker studies. Of particular concern is the adequacy of recorded doses received in the early years of operations at older nuclear installations, such as the potential for 'missed' photon doses. A further issue is how baseline cancer rates may influence radiation-related excess risks. There is scope for a considerable increase in the statistical power of worker studies, with longer follow-up capturing more deaths and incident cases of cancer, and further workforces being included in collaborative studies, but the difficulties posed by dosimetry questions should not be ignored and need to be the subject of detailed scrutiny.

Mortality from Leukemia, Cancer and Heart Disease among U.S. Nuclear Power Plant Workers, 1957-2011

BACKGROUND

The aim of the Million Person Study (MPS) of Low Dose Health Effects is to examine the level of radiation risk for chronic exposures received gradually over time and not acutely as was the case for the Japanese atomic bomb survivors. Nuclear power plant (NPP) workers comprise nearly 15 percent of the MPS. Leukemia, selected cancers, Parkinson's disease, ischemic heart disease (IHD) and other causes of death are evaluated.

METHODS AND MATERIAL

The U.S. Nuclear Regulatory Commission's Radiation Exposure Information and Reporting System (REIRS) and the Landauer, Inc. dosimetry databases identified 135,193 NPP workers first monitored 1957-1984. Annual personal dose equivalents [Hp(10)] were available for each worker. Radiation records from all places of employment were sought. Vital status was determined through 2011. Mean absorbed doses to red bone marrow (RBM), esophagus, lung, colon, brain and heart were estimated by adjusting the recorded Hp(10) for each worker by scaling factors, accounting for exposure geometry and energy of the incident gamma radiation. Standardized mortality ratios (SMR) were calculated. Radiation risks were estimated using Cox proportional hazards models.

RESULTS

Nearly 50% of workers were employed for more than 20 years. The mean duration of follow-up was 30.2 y. Overall, 29,076 total deaths occurred, 296 from leukemia other than chronic lymphocytic leukemia (CLL), 3,382 from lung cancer, 140 from Parkinson's disease and 5,410 from IHD. The mean dose to RBM was 37.9 mGy (maximum 1.0 Gy; percent >100 mGy was 9.2%), 43.2 mGy to lung, 43.7 mGy to colon, 33.2 mGy to brain, and 43.9 mGy to heart. The SMRs (95% CI) were 1.06 (0.94;1.19) for leukemia other than CLL, 1.10 (1.07;1.14) for lung cancer, 0.90 (0.76;1.06) for Parkinson's disease, and 0.80 (0.78; 0.82) for IHD. The excess relative risk (ERR) per 100 mGy for leukemia other than CLL was 0.15 (90% CI 0.001; 0.31). For all solid cancers the ERR per 100 mGy (95% CI) was 0.01 (-0.03; 0.05), for lung cancer -0.04 (-0.11; 0.02), for Parkinson's disease 0.24 (-0.02; 0.50), and for IHD -0.01 (-0.06; 0.04).

CONCLUSION

Prolonged exposure to radiation increased the risk of leukemia other than CLL among NPP workers. There was little evidence for a radiation-association for all solid cancers, lung cancer or ischemic heart disease. Increased precision will be forthcoming as the different cohorts within the MPS are combined, such as industrial radiographers and medical radiation workers who were assembled and evaluated in like manner.

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.

Radium dial workers: back to the future

PURPOSE

This paper reviews the history of the radium dial workers in the United States, summarizes the scientific progress made since the last evaluation in the early 1990s, and discusses current progress in updating the epidemiologic cohort and applying new dosimetric models for radiation risk assessment.

BACKGROUND

The discoveries of radiation and radioactivity led quickly to medical and commercial applications at the turn of the 20th century, including the development of radioluminescent paint, made by combining radium with phosphorescent material and adhesive. Workers involved with the painting of dials and instruments included painters, handlers, ancillary workers, and chemists who fabricated the paint. Dial painters were primarily women and, prior to the mid to late 1920s, would use their lips to give the brush a fine point, resulting in high intakes of radium. The tragic experience of the dial painters had a significant impact on industrial safety standards, including protection measures taken during the Manhattan Project. The dial workers study has formed the basis for radiation protection standards for intakes of radionuclides by workers and the public.

EPIDEMIOLOGIC APPROACH

The mortality experience of 3,276 radium dial painters and handlers employed between 1913 and 1949 is being determined through 2019. The last epidemiologic follow-up was 30 years ago when most of these workers were still alive. Nearly 65% were born before 1920, 37.5% were teenagers when first hired, and nearly 50% were hired before 1930 when the habit of placing brushes in mouths essentially stopped. Comprehensive dose reconstruction techniques are being applied to estimate organ doses for each worker related to the intake of 226Ra, 228Ra, and associated photon exposures. Time dependent dose-response analyses will estimate lifetime risks for specific causes of death.

DISCUSSION

The study of radium dial workers is part of the Million Person Study of low-dose health effects that is designed to evaluate radiation risks among healthy American workers and veterans. Despite being one of the most important and influential radiation effects studies ever conducted, shifting programmatic responsibilities and declining funding led to the termination of the radium program of studies in the early 1990s. Renewed interest and opportunity have arisen. With scientific progress made in dosimetric methodology and models, the ability to perform a study over the entire life span, and the potential applicability to other scenarios such as medicine, environmental contamination and space exploration, the radium dial workers have once again come to the forefront.

Using personal monitoring data to derive organ doses for medical radiation workers in the Million Person Study-considerations regarding NCRP Commentary no. 30

The study of low dose and low-dose rate exposure is of central importance in understanding the possible range of health effects from prolonged exposures to radiation. The One Million Person Study of Radiation Workers and Veterans (MPS) of low-dose health effects was designed to evaluate radiation risks among healthy American workers and veterans. The MPS is evaluating low-dose and dose-rate effects, intakes of radioactive elements, cancer and non-cancer outcomes, as well as differences in risks between women and men. Medical radiation workers make up a large group of individuals occupationally exposed to low doses of radiation from external x-ray/gamma exposures. For the MPS, about 100 000 United States medical radiation workers have been selected for study. The approach to the complex dosimetry circumstances for such workers over three to four decades of occupation were initially and broadly described in National Council on Radiation Protection and Measurements (NCRP) Report No. 178. NCRP Commentary No. 30 provides more detail and describes an optimum approach for using personal monitoring data to estimate lung and other organ doses applicable to the cohort and provides specific precautions/considerations applicable to the dosimetry of medical radiation worker organ doses for use in epidemiologic studies. The use of protective aprons creates dosimetric complexity. It is recommended that dose values from dosimeters worn over a protective apron be reduced by a factor of 20 for estimating mean organ doses to tissues located in the torso and that 15% of the marrow should be assumed to remain unshielded for exposure scenarios when aprons are worn. Conversion coefficients relating personal dose equivalent,H_p(10) in mSv, to mean absorbed doses to organs and tissues,D_Tin mGy, for females and males for six exposure scenarios have been determined and presented for use in the MPS. This Memorandum summarises several key points in NCRP Commentary No. 30.

Effects of exposure to low-dose ionizing radiation on changing platelets: a prospective cohort study

Background

Numerous studies have concentrated on high-dose radiation exposed accidentally or through therapy, and few involve low-dose occupational exposure, to investigate the correlation between low-dose ionizing radiation and changing hematological parameters among medical workers.

Methods

Using a prospective cohort study design, we collected health examination reports and personal dose monitoring data from medical workers and used Poisson regression and restricted cubic spline models to assess the correlation between changing hematological parameters and cumulative radiation dose and determine the dose-response relationship.

Results

We observed that changing platelet of 1265 medical workers followed up was statistically different among the cumulative dose groups (P = 0.010). Although the linear trend tested was not statistically significant (P_trend = 0.258), the non-linear trend tested was statistically significant (P_non-linear = 0.007). Overall, there was a correlation between changing platelets and cumulative radiation dose (a change of β^a 0.008 × 10⁹/L during biennially after adjusting for gender, age at baseline, service at baseline, occupation, medical level, and smoking habits; 95% confidence interval [CI] = 0.003,0.014 × 10⁹/L). Moreover, we also found positive first and then negative dose-response relationships between cumulative radiation dose and changing platelets by restricted cubic spline models, while there were negative patterns of the baseline service not less than 10 years (− 0.015 × 10⁹/L, 95% CI = − 0.024, − 0.007 × 10⁹/L) and radiation nurses(− 0.033 × 10⁹/L, 95% CI = − 0.049, − 0.016 × 10⁹/L).

Conclusion

We concluded that although the exposure dose was below the limit, medical workers exposed to low-dose ionizing radiation for a short period of time might have increased first and then decreased platelets, and there was a dose-response relationship between the cumulative radiation dose and platelets changing.

The Effect of Low Temperatures on Environmental Radiation Damage in Living Systems: Does Hypothermia Show Promise for Space Travel?

Low-temperature treatments (i.e., hypothermia) may be one way of regulating environmental radiation damage in living systems. With this in mind, hibernation under hypothermic conditions has been proposed as a useful approach for long-term human space flight. However, the underlying mechanisms of hypothermia-induced radioresistance are as yet undetermined, and the conventional risk assessment of radiation exposure during hibernation remains insufficient for estimating the effects of chronic exposure to galactic cosmic rays (GCRs). To promote scientific discussions on the application of hibernation in space travel, this literature review provides an overview of the progress to date in the interdisciplinary research field of radiation biology and hypothermia and addresses possible issues related to hypothermic treatments as countermeasures against GCRs. At present, there are concerns about the potential effects of chronic radiation exposure on neurological disorders, carcinogenesis, ischemia heat failures, and infertility in astronauts; these require further study. These concerns may be resolved by comparing and integrating data gleaned from experimental and epidemiological studies.

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.

Evolution of radiation protection for medical workers

Within a few months of discovery, X-rays were being used worldwide for diagnosis and within a year or two for therapy. It became clear very quickly that while there were immense benefits, there were significant associated hazards, not only for the patients, but also for the operators of the equipment. Simple radiation protection measures were implemented within a decade or two and radiation protection for physicians and other operators has continued to evolve over the last century driven by cycles of widening uses, new technologies, realization of previously unidentified effects, development of recommendations and regulations, along with the rise of related societies and professional organizations. Today, the continue acceleration of medical radiation uses in diagnostic imaging and in therapeutic modalities not imagined at the turn of this century, such as positron emission tomography, calls for constant vigilance and flexibility to provide adequate protection for the growing numbers of medical radiation workers.

Radiation epidemiology and health effects following low-level radiation exposure

Radiation epidemiology is the study of human disease following radiation exposure to populations. Epidemiologic studies of radiation-exposed populations have been conducted for nearly 100 years, starting with the radium dial painters in the 1920s and most recently with large-scale studies of radiation workers. As radiation epidemiology has become increasingly sophisticated it is used for setting radiation protection standards as well as to guide the compensation programmes in place for nuclear weapons workers, nuclear weapons test participants, and other occupationally exposed workers in the United States and elsewhere. It is known with high assurance that radiation effects at levels above 100-150 mGy can be detected as evidenced in multiple population studies conducted around the world. The challenge for radiation epidemiology is evaluating the effects at low doses, below about 100 mGy of low-linear energy transfer radiation, and assessing the risks following low dose-rate exposures over years. The weakness of radiation epidemiology in directly studying low dose and low dose-rate exposures is that the signal, i.e. the excess numbers of cancers associated with low-level radiation exposure, is so very small that it cannot be seen against the very high background occurrence of cancer in the population, i.e. a lifetime risk of incidence reaching up to about 38% (i.e. 1 in 3 persons will develop a cancer in their lifetime). Thus, extrapolation models are used for the management of risk at low doses and low dose rates, but having adequate information from low dose and low dose-rate studies would be highly desirable. An overview of recently conducted radiation epidemiologic studies which evaluate risk following low-level radiation exposures is presented. Future improvements in risk assessment for radiation protection may come from increasingly informative epidemiologic studies, combined with mechanistic radiobiologic understanding of adverse outcome pathways, with both incorporated into biologically based models.

What does radiation biology tell us about potential health effects at low dose and low dose rates?

The health risks to humans exposed to low dose and low dose rate ionising radiation remain ambiguous and are the subject of debate. The need to establish risk assessment standards based on the mechanisms underlying low dose/low fluence radiation exposures has been recognised by scholarly and regulatory bodies as critical for reducing the uncertainty in predicting adverse health risks of human exposure to low doses of radiation. Here, a brief review of laboratory-based evidence of molecular and biochemical changes induced by low doses and low dose rates of radiation is presented. In particular, two phenomena, namely bystander effects and adaptive responses that may impact low-level radiation health risks, are discussed together with the need for further studies. The expansion of this knowledge by considering the important variables that affect the radiation response (e.g. genetic susceptibility, time after exposure), and using the latest advances in experimental models and bioinformatics tools, may guide epidemiological studies towards reducing the uncertainty in predicting the potential health hazards of exposure to low-dose radiation.

Studies of radiation health effects inform EPA actions

In 1970, the US Environmental Protection Agency (EPA) was given the responsibility to provide guidance to other federal agencies in the formulation of radiation protection standards. To carry out its federal guidance responsibilities and protect human health, the EPA must estimate risk at low doses to limit the risk of radiogenic cancers from environmental exposures. These risk estimates are based on models which conform to the linear no threshold (LNT) hypothesis. A cancer risk model conforms to the LNT hypothesis if the excess risk of cancer at low doses increases approximately proportional to dose, with no threshold. Risk models with a linear-quadratic dose response can satisfy the LNT hypothesis. Based on careful review of evidence from epidemiological and radiobiological studies, authoritative scientific bodies have repeatedly endorsed the use of LNT models for estimating and regulating risk and concluded that despite uncertainties at low dose and dose rates, the LNT model remains the most practical and implementable model for radiation protection. This article describes the rationale underlying the use of LNT models for calculating risk for low dose and dose rate exposures and discusses some of the epidemiological evidence which inform on its continued use.

Asbestos Exposure and Mesothelioma Mortality among Atomic Veterans

BACKGROUND

During the Cold War the United States (U.S.) conducted 230 above-ground atmospheric nuclear weapons tests between 1945 and 1962 at the Nevada Test Site and the Pacific Proving Grounds. These tests involved over 250,000 military personnel. Asbestos was used on the naval vessels for insulation in the boiler room, engine room, and other areas. 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, developed using historical records provided by the Defense Threat Reduction Agency. 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 Pacific Proving Ground (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

Although jobs with high potential for exposure to asbestos products were held by only 20% of the enlisted naval population, sailors with these jobs (machinist's mate, pipe fitter, boiler technician, water tender and fireman) experienced 55% of mesothelioma deaths. The significantly higher mortality rate overall was explained by asbestos exposure among enlisted naval personnel in this low-dose radiation exposed cohort.