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The scientific question of whether protracted low-dose or low-dose-rate exposure to external radiation is causally related to the risk of circulatory disease continues to be an important issue for radiation protection. Previous analyses of a matched case-control dataset nested in a large cohort of UK nuclear fuel cycle workers indicated that there was little evidence that observed associations between external radiation dose and ischemic heart disease (IHD) mortality risk [OR = 1.35 (95% CI: 0.99-1.84) for 15-year-lagged exposure] could alternatively be explained by confounding from pre-employment tobacco smoking, BMI or blood pressure, or from socioeconomic status or occupational exposure to excessive noise or shiftwork. To improve causal inference about the observed external radiation dose and IHD mortality association, we estimated the potential magnitude and direction of non-random errors, incorporated sensitivity analyses and simulated bias effects under plausible scenarios. We conducted quantitative bias analyses of plausible scenarios based on 1,000 Monte Carlo samples to explore the impact of exposure measurement error, missing information on tobacco smoking, and unmeasured confounding, and assessed whether observed associations were reliant on the inclusion of specific matched pairs using bootstrapping with 10% of matched pairs randomly excluded in 1,000 samples. We further explored the plausibility that having been monitored for internal exposure, which was an important confounding factor in the case-control analysis for which models were adjusted, was indeed a confounding factor or whether it might have been the result of some form of selection bias. Consistent with the broader epidemiological evidence-base, these analyses provide further evidence that the dose-response association between cumulative external radiation exposure and IHD mortality is non-linear in that it has a linear shape plateauing at an excess risk of 43% (95% CI: 7-92%) on reaching 390 mSv. Analyses of plausible scenarios of patterns of missing data for tobacco smoking at start of employment indicated that this resulted in relatively little bias towards the null in the original analysis. An unmeasured confounder would have had to have been highly correlated (rp > 0.60) with cumulative external radiation dose to importantly bias observed associations. The confounding effect of "having been monitored for internal dose" was unlikely to have been a true confounder in a biological sense, but instead may have been some unknown factor related to differences over time and between sites in selection criteria for internal monitoring, possibly resulting in collider bias. Plausible patterns of exposure measurement error negatively biased associations regardless of the modeled scenario, but did not importantly change the shape of the observed dose-response associations. These analyses provide additional support for the hypothesis that the observed association between external radiation exposure and IHD mortality may be causal., (©2021 by Radiation Research Society. All rights of reproduction in any form reserved.)

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., (Creative Commons Attribution license.)

Epidemiological studies have suggested a link between low-level radiation exposure and an increased risk of cardiovascular disease, but the possibility of bias or confounding must be considered. We analyzed data from a matched case-control study nested in a cohort of British male industrial (i.e., blue-collar) nuclear fuel cycle workers using paired conditional logistic regression. The cases were comprised of workers from two nuclear sites who had died from ischemic heart disease (IHD) and were matched to controls on nuclear site, date of birth and first year of employment (1,220 pairs). Radiation doses from external sources and to the liver from internally deposited plutonium and uranium were obtained. Models were adjusted for age at start of employment at either site, decade of start, age at exit from study (death or censoring), process/other worker and socio-economic status. Included potential confounding factors of interest were occupational noise, shift work, pre-employment blood pressure, body mass index and tobacco smoking. Cumulative external doses ranged from 0-1,656 mSv and cumulative internal doses for those monitored for radioactive intakes ranged from 0.004-5,732 mSv. In a categorical analysis, additionally adjusted for whether or not a worker was monitored for internal exposure, IHD mortality risk was associated with cumulative external unlagged dose with a 42% excess risk (95% CI: 4%, 95%) at >103 mSv (highest quartile relative to lowest quartile), and 35% (95% CI: -1%, 84%) at >109 mSv 15-year lagged dose. The log-linear increase in risk per 100 mSv was 2% (95% CI: -4%, 8%) for unlagged external dose and 5% (95% CI: -2%, 11%) for 15-year lagged dose. Associations with external dose for workers monitored only for exposure to external radiation reflected those previously reported for the cohort from which the cases and controls were drawn. There was little evidence of excess risk associated with cumulative doses from internal sources, which had not been assessed in the cohort study. The impact of the included potential confounding variables was minimal, with the possible exception of occupational noise exposure. Subgroup analyses indicated evidence of heterogeneity between sites, occupational groups and employment duration, and an important factor was whether workers were monitored for the potential presence of internal emitters, which was not explained by other factors included in the study. In summary, we found evidence for an increased IHD mortality risk associated with external radiation dose, but little evidence of an association with internal dose. External dose associations were minimally affected by important confounders. However, the considerable heterogeneity in the associations with external doses observed between subgroups of workers is difficult to explain and requires further work., (©2020 by Radiation Research Society. All rights of reproduction in any form reserved.)

The potential for adverse health effects from internal exposure to Plutonium has been recognised since its discovery in the 1940s. However, in the absence of specific information, potential risks from Plutonium exposure have always largely been controlled through knowledge of radiation exposure risks in general, much of which comes from external radiation exposures. To try to obtain more direct estimates of potential internal exposure risks, epidemiological studies of Plutonium workers need to be conducted. Such epidemiological analyses require individual Plutonium exposure estimates that are as accurate and unbiased as possible. The UK Sellafield workforce includes one of the world's largest cohorts of Plutonium workers, which constitutes, by some considerable margin, the group of workers most comprehensively monitored for internal exposure to this alpha-particle-emitter. However, for several hundred workers employed at the start of Plutonium work at the facility, during the period from 1952 through to 1963, the historical urinalysis results available cannot provide sufficiently accurate and unbiased exposure assessments needed for use in epidemiological studies. Consequently, these early workers have had to be excluded from epidemiological analyses and this has significantly reduced the power of these studies. A promising quantitative methodology to overcome the issue of missing or deficient exposure data, is to use exposure data from other sources to estimate the average exposure a 'typical worker' would have received, and to collate this information for specific occupations and years. This approach is called a Job-Exposure Matrix (JEM). Work on a pilot study to construct a population-specific quantitative JEM for the early Plutonium workers at Sellafield during 1952-1963, for whom reliable urinalysis results do not exist, has shown the potential for a JEM approach to produce more reliable and useful exposure estimates for epidemiological research.

Plutonium is a radiologically significant alpha-particle emitter. The potential for adverse health effects from internal exposures due to plutonium intakes has been recognized since the 1940s. The workforce of the Sellafield nuclear facility (Cumbria, UK), includes one of the world's most important groups of plutonium-exposed workers for studying the potential health risks of this internal exposure. However, for several hundred workers employed at the start of plutonium work at the facility (1952-1963), historical monitoring records based on measurements of urinary excretion of plutonium are not sufficiently reliable to provide the accurate and unbiased exposure assessments needed for epidemiological studies. Consequently, these early workers have had to be excluded from such studies, significantly reducing their power. We constructed a population-specific quantitative job exposure matrix (JEM) to estimate the average intakes of "typical plutonium workers" in this period, from 1952-1963, and assessed its validity and sensitivity to exposure assessment decisions. We conducted internal cross-validation using an a priori 10% extracted sample to evaluate reliability of estimates, explored JEM sensitivity to assumptions in the exposure assessment, and assessed the impact of uncertainty in urinalysis measurements on the precision of annual intake estimates using Markov Chain Monte Carlo (MCMC) methodology. Pairwise correlations ( R P ) of estimated (JEM) and measured (10% sample) annual intakes were moderate to high ( R P > 0.4) for 10 out of 13 JEM groups, while absolute differences were <20% for 11 out of 13 JEM groups. There was little evidence of a temporal trend in correlations ( P = 0.13) or absolute differences ( P = 0.34). The median JEM-derived cumulative intake of 95.2 (IQR, 55.0-130.0) Bq was comparable to those based on alternative assumptions in the exposure assessment (median range, 95.2-100.0 Bq; 75th percentiles, 130.0-146.0 Bq). Measurement error simulation resulted in a 40-60% reduced median cumulative intake but higher maximum cumulative intakes. The JEM finds a balance between reliability and precision that makes it useful for epidemiological purposes and is relatively insensitive to specific choices in the exposure assessment. This JEM will allow the inclusion of workers with longest follow-up and who could not be included up until now in epidemiological studies without introducing significant bias.

Any potential health effects of radiation emitted from radionuclides deposited in the bodies of workers exposed to radioactive materials can be directly investigated through epidemiological studies. However, estimates of radionuclide exposure and consequent tissue-specific doses, particularly for early workers for whom monitoring was relatively crude but exposures tended to be highest, can be uncertain, limiting the accuracy of risk estimates. We review the use of job-exposure matrices (JEMs) in peer-reviewed epidemiological and exposure assessment studies of nuclear industry workers exposed to radioactive materials as a method for addressing gaps in exposure data, and discuss methodology and comparability between studies. We identified nine studies of nuclear worker cohorts in France, Russia, the USA and the UK that had incorporated JEMs in their exposure assessments. All these JEMs were study or cohort-specific, and although broadly comparable methodologies were used in their construction, this is insufficient to enable the transfer of any one JEM to another study. Moreover there was often inadequate detail on whether, or how, JEMs were validated. JEMs have become more detailed and more quantitative, and this trend may eventually enable better comparison across, and the pooling of, studies. We conclude that JEMs have been shown to be a valuable exposure assessment methodology for imputation of missing exposure data for nuclear worker cohorts with data not missing at random. The next step forward for direct comparison or pooled analysis of complete cohorts would be the use of transparent and transferable methods.

Many individuals are, or have been, exposed to ionising radiation in the course of their work and the epidemiological study of occupationally irradiated groups offers an important opportunity to complement the estimates of risks to health resulting from exposure to radiation that are obtained from other populations, such as the Japanese survivors of the atomic bombings of Hiroshima and Nagasaki in 1945. Moreover, workplace exposure to radiation usually involves irradiation conditions that are of direct relevance to the principal concern of radiological protection: protracted exposure to low level radiation. Further, some workers have been exposed to radioactive material that has been inadvertently taken into the body, and the study of these groups leads to risk estimates derived directly from the experience of those irradiated by these 'internal emitters', intakes of alpha-particle-emitters being of particular interest. Workforces that have been the subject of epidemiological study include medical staff, aircrews, radium dial luminisers, underground hard-rock miners, Chernobyl clean-up workers, nuclear weapons test participants and nuclear industry workers. The first solid epidemiological evidence of the stochastic effects of irradiation came from a study of occupational exposure to medical x-rays that was reported in 1944, which demonstrated a large excess risk of leukaemia among US radiologists; but the general lack of dose records for early medical staff who tended to experience the highest exposures hampers the derivation of risks per unit dose received by medical workers. The instrument dial luminisers who inadvertently ingested large amounts of radium-based paint and underground hard-rock miners who inhaled large quantities of radon and its decay products suffered markedly raised excess risks of, respectively, bone and lung cancers; the miner studies have provided standard risk estimates for radon-induced lung cancer. The large numbers of nuclear industry workers around the world present a possibility of deriving risk coefficients of direct relevance to radiological protection, and the recently published study of workers from 15 countries illustrates what can be achieved by international collaboration. However, it would appear that there are some problems with this study that require attention before reliance can be placed upon the results. Early workers from the Mayak plutonium production facility in Russia were heavily exposed to external sources of penetrating radiation and to plutonium, and appreciable effort has been expended in obtaining dependable risk estimates from this scientifically valuable group of workers. Those occupationally exposed to low levels of radiation also present an opportunity of studying possible somatic health effects other than cancer, such as heart disease and eye cataracts, that are the subject of much discussion at present. Overall, studies of exposure to ionising radiation in the workplace provide a valuable support to studies of those groups exposed under other circumstances, and in some instances (such as exposure to plutonium) effectively offer the only direct source of epidemiological evidence on risks.

BACKGROUND: Although high doses of ionizing radiation have long been linked to circulatory disease, evidence for an association at lower exposures remains controversial. However, recent analyses suggest excess relative risks at occupational exposure levels. OBJECTIVES: We performed a systematic review and meta-analysis to summarize information on circulatory disease risks associated with moderate- and low-level whole-body ionizing radiation exposures. METHODS: We conducted PubMed/ISI Thomson searches of peer-reviewed papers published since 1990 using the terms radiation AND heart AND disease, OR radiation AND stroke, OR radiation AND circulatory AND disease. Radiation exposures had to be whole-body, with a cumulative mean dose of < 0.5 Sv, or at a low dose rate (< 10 mSv/day). We estimated population risks of circulatory disease from low-level radiation exposure using excess relative risk estimates from this meta-analysis and current mortality rates for nine major developed countries. RESULTS: Estimated excess population risks for all circulatory diseases combined ranged from 2.5%/Sv [95% confidence interval (CI): 0.8, 4.2] for France to 8.5%/Sv (95% CI: 4.0, 13.0) for Russia. CONCLUSIONS: Our review supports an association between circulatory disease mortality and low and moderate doses of ionizing radiation. Our analysis was limited by heterogeneity among studies (particularly for noncardiac end points), the possibility of uncontrolled confounding in some occupational groups by lifestyle factors, and higher dose groups (> 0.5 Sv) generally driving the observed trends. If confirmed, our findings suggest that overall radiation-related mortality is about twice that currently estimated based on estimates for cancer end points alone (which range from 4.2% to 5.6%/Sv for these populations).

In the United Kingdom, the Nuclear Installations Act 1965 places a 'strict' statutory duty on the operators of nuclear facilities to ensure that any exposure to radiation resulting from operations does not cause injury or damage. A claimant does not have to prove fault to receive compensation under the Act, only causation. The 1965 Act has been fundamental in shaping litigation involving the nuclear industry in the UK. Civil law cases brought under the Act will be heard before a single judge (with no jury or technical assessor) who must present his or her decision in a reasoned judgment. This process leads to a considerable volume of expert evidence being presented to the court and extensive cross-examination of witnesses. The expense and uncertainoutcome of cases involving claims by nuclear workers that occupational exposure to radiation had caused the development of cancer has ledto employers and trade unions setting up the voluntary Compensation Scheme for Radiation-linked Diseases as an alternative to litigation.This Scheme has worked well and is held up as a model of alternativedispute resolution. However, a few cases concerning personal injury or damage to property have come before the courts when the defendant nuclear operator considered that the claims were technically unjustified and where settlement was not a policy option. As anticipated, these cases were lengthy, complex, and expensive. The radiation doses assessed to have been received by the individuals who were the subject of claims, whether workers or members of the public, have been crucial to the outcome. The technical expertise of health physicists and allied specialists has been vital in establishing defensible estimates of dose, and this contribution can be expected to remain of high importance in radiation litigation in the UK. [ABSTRACT FROM AUTHOR]

The assumption that any additional exposure to ionizing radiation leads to an increase in the risk of stochastic health effects implies that some cases of these effects will be caused by exposure incurred occupationally. The main health effect expected to arise in the exposed individuals is cancer. Such radiation-induced cancers cannot be distinguished from the far larger number of background cancers, and, therefore, causation must be assessed statistically. The probability of causation methodology has been developed to ascertain the likelihood that a particular cancer may be attributed to a particular prior exposure to radiation. Given the pertinent details of an individual case,a probability of causation value is calculated from the appropriate relative risk obtained from radiation risk models derived from the epidemiological study of exposed populations, although there are many uncertainties inherent in a particular probability of causation calculation. In the United Kingdom, the Compensation Scheme for Radiation-linked Diseases has been created to determine whether those individuals occupationally exposed to radiation in the nuclear industry who have subsequently developed a malignant disease should be compensated. The Scheme is a voluntary arrangement based upon the probability of causation methodology, which incorporates various procedures agreed by employer and employee representatives and their advisers. In a pragmatic approach to compensation, the uncertainties of a specific probability of causation calculation are accommodated through generosity factors which favor the claimant and encourage the use of the Scheme. The Scheme, which was introduced in 1982 and modified in 1987 and 1991 in the light of operational experience and revised risk estimates, has provided a successful alternative to litigation from the point of view of both employer and employee. [ABSTRACT FROM AUTHOR]

We constructed a database containing birth certificate details of all 261,176 live births and 4059 stillbirths in Cumbria, in northwest England, from 1950 to 1989 for use as an epidemiological tool to examine the health of those who had parents employed at the nuclear installation, Sellafield, in particular in relation to the occupational radiation dose which the parents might have received while working therebefore their children were conceived. A computer database containingpersonal details of all 25,514 individuals employed at Sellafield over this period is maintained at Sellafield for epidemiological research purposes. A computer linkage exercise was carried out to match parents in the Cumbrian births database with these Sellafield employees.Ambiguous links were resolved by a clerical team who had access to paper records at Sellafield containing further employee details. Usingthe National Health Service Central Register, death, cancer, and emigration registrations occurring among the Cumbrian birth cohort before the end of 1989 were identified and entered into the database. 18,454 births were linked to 10,092 Sellafield employees. The 261,176 live births were also linked to 7318 deaths and 1716 cancer registrations. Thus we were able to identify and study the complete cohort of Cumbrian-bom offspring of the Sellafield work force over a 40-year time period and compare the health outcome data of our exposed population with that of a large geographical area with a substantial population.The database construction demonstrates the feasibility of large-scale cohort studies of the effects of occupational and environmental exposures. [ABSTRACT FROM AUTHOR]