Mortality associated with chronic external radiation exposure in the French combined cohort of nuclear workers

Finite-Sample Bias of the Linear Excess Relative Risk in Cohort Studies of Computed Tomography-Related Radiation Exposure and Cancer

The linear excess relative risk (ERR) is the most commonly reported measure of association in radiation epidemiological studies, when individual dose estimates are available. While the asymptotic properties of the ERR estimator are well understood, there is evidence of small sample bias in case-control studies of treatment-related radiation exposure and second cancer risk. Cohort studies of cancer risk after exposure to low doses of radiation from diagnostic procedures, e.g., computed tomography (CT) examinations, typically have small numbers of cases and risks are small. Therefore, understanding the properties of the estimated ERR is essential for interpretation and analysis of such studies. We present results of a simulation study that evaluates the finite-sample bias of the ERR estimated by time-to-event analyses and its confidence interval using simulated data, resembling a retrospective cohort study of radiation-related leukemia risk after CT examinations in childhood and adolescence. Furthermore, we evaluate how the Firth-corrected estimator reduces the finite-sample bias of the classical estimator. We show that the ERR is overestimated by about 30% for a cohort of about 150,000 individuals, with 42 leukemia cases observed on average. The bias is reduced for higher baseline incidence rates and for higher values of the true ERR. As the number of cases increases, the ERR is approximately unbiased. The Firth correction reduces the bias for all cohort sizes to generally around or under 5%. Epidemiological studies showing an association between radiation exposure from pediatric CT and cancer risk, unless very large, may overestimate the magnitude of the relationship, while there is no evidence of an increased chance for false-positive results. Conducting large studies, perhaps by pooling individual studies to increase the number of cases, should be a priority. If this is not possible, Firth correction should be applied to reduce small-sample bias.

Exposure to low-dose radiation in occupational settings and ischaemic heart disease: a systematic review and meta-analysis

Ionising radiation is a human carcinogen, but the evidence is less clear that exposure to low-dose ionising radiation (LDIR) increases the risk of adverse cardiovascular outcomes. We synthesised the literature of chronic occupational exposure to LDIR and cardiovascular disease, particularly for ischaemic heart disease (IHD).The literature search was conducted using three databases including studies published between 1990 and 2022. A quality assessment of the studies was completed using the Office of Health and Assessment and Translation Risk of Bias Rating Tool. We conducted meta-analyses for IHD mortality using random effects models using measures of excess relative risk per sievert (ERR/Sv) obtained from internal cohort comparisons, as well as with standardised mortality ratios (SMRs) from external cohort comparisons.We identified 2189 articles, and of these, 26 provided data on IHD and were retained. Most studies were classified as having a 'moderate' level of risk of bias. Fourteen and 10 studies reporting external radiation doses were included in meta-analyses using SMR and ERR/Sv, respectively. The meta-summary SMR was 0.81 (95% CI 0.74 to 0.89) with evidence of reduced risk but high heterogeneity across studies. For internal cohort measures, the summary ERR/Sv for a lagged exposure of 10 years was 0.10 (95% CI 0.01 to 0.20) with low heterogeneity. The subgroup analysis by lagged exposure time showed the strongest association were for the 15 and 20 years lag.Our findings suggest that occupational exposure to LDIR increases the risk IHD mortality and highlight the relevance of internal cohort comparisons.

Cancer mortality after low dose exposure to ionising radiation in workers in France, the United Kingdom, and the United States (INWORKS): cohort study

OBJECTIVE

To evaluate the effect of protracted low dose, low dose rate exposure to ionising radiation on the risk of cancer.

DESIGN

Multinational cohort study.

SETTING

Cohorts of workers in the nuclear industry in France, the UK, and the US included in a major update to the International Nuclear Workers Study (INWORKS).

PARTICIPANTS

309 932 workers with individual monitoring data for external exposure to ionising radiation and a total follow-up of 10.7 million person years.

MAIN OUTCOME MEASURES

Estimates of excess relative rate per gray (Gy) of radiation dose for mortality from cancer.

RESULTS

The study included 103 553 deaths, of which 28 089 were due to solid cancers. The estimated rate of mortality due to solid cancer increased with cumulative dose by 52% (90% confidence interval 27% to 77%) per Gy, lagged by 10 years. Restricting the analysis to the low cumulative dose range (0-100 mGy) approximately doubled the estimate of association (and increased the width of its confidence interval), as did restricting the analysis to workers hired in the more recent years of operations when estimates of occupational external penetrating radiation dose were recorded more accurately. Exclusion of deaths from lung cancer and pleural cancer had a modest effect on the estimated magnitude of association, providing indirect evidence that the association was not substantially confounded by smoking or occupational exposure to asbestos.

CONCLUSIONS

This major update to INWORKS provides a direct estimate of the association between protracted low dose exposure to ionising radiation and solid cancer mortality based on some of the world's most informative cohorts of radiation workers. The summary estimate of excess relative rate solid cancer mortality per Gy is larger than estimates currently informing radiation protection, and some evidence suggests a steeper slope for the dose-response association in the low dose range than over the full dose range. These results can help to strengthen radiation protection, especially for low dose exposures that are of primary interest in contemporary medical, occupational, and environmental settings.

Ionizing radiation and solid cancer mortality among US nuclear facility workers

BACKGROUND

The risk of solid cancers from low-level protracted ionizing radiation is not well characterized. Nuclear workers provide valuable information on the effects of ionizing radiation in contemporary exposure scenarios relevant to workers and the public.

METHODS

We evaluated the association between penetrating ionizing radiation exposure and solid cancer mortality among a pooled cohort of nuclear workers in the USA, with extended follow-up to examine cancers with long latencies. This analysis includes 101 363 workers from five nuclear facilities, with 12 069 solid cancer deaths between 1944 and 2016. The association between cumulative equivalent dose measured in sieverts (Sv) and solid cancer subtypes were modelled as the excess relative rate per Sv (ERR Sv-1) using Cox regression.

RESULTS

For the association between ionizing radiation exposure and all solid cancer mortality we observed an elevated rate (ERR Sv-1=0.19; 95% CI: -0.10, 0.52), which was higher among a contemporary sub-cohort of workers first hired in 1960 or later (ERR Sv-1= 2.23; 95% CI: 1.13, 3.49). Similarly, we observed an elevated rate for lung cancer mortality (ERR Sv-1= 0.65; 95% CI: 0.09, 1.30) that was higher among contemporary hires (ERR Sv-1= 2.90; 95% CI: 1.00, 5.26).

CONCLUSIONS

Although concerns remain about confounding, measurement error and precision, this analysis strengthens the evidence base indicating there are radiogenic risks for several solid cancer types.

Epidemiology of stroke and transient ischemic attacks in the population of the territories adjacent to the former Semipalatinsk Nuclear Test Site, Kazakhstan

The issue of radiation exposure as a potential cause of cerebrovascular disease raises many concerns. The aim of the present study was to investigate the epidemiology of stroke and transient ischemic attacks (TIA) along with the associated risk factors among the population of East Kazakhstan exposed to ionising radiation from the former Semipalatinsk Nuclear Test Site (SNTS) in comparison with the unexposed population of the same region. This 5-year retrospective cross-sectional study included the data on 10,970 patients, of whom the majority (62.3%) suffered from ischemic stroke, 11.7% had hemorrhagic stroke and the remaining 26.0% had TIA. At the moment when stroke/TIA happened, exposed patients were younger than the unexposed (mean age 63 years versus 64 years, p < 0.001) and showed higher rates of nearly all associated comorbidities, which commonly were more severe. Besides, exposed patients showed a higher risk of stroke lethality in contrast with the unexposed. The observed features might indicate that people residing in the vicinity of the SNTS are vulnerable to cerebrovascular disease and thus, this study contributes to timely recognition of this public health problem. In addition, a longitudinal study has to be envisaged to clarify whether there is any cause-effect relationship between exposure to radiation from the SNTS and the development of stroke or transient ischemic attacks.

Reanalysis of cancer mortality using reconstructed organ-absorbed dose: J-EPISODE 1991‒2010

The Japanese Epidemiological Study on Low-Dose Radiation Effects (J-EPISODE) has been conducted since 1990 by the Radiation Effects Association to analyse health effects for nuclear workers. It uses the recorded doses, i.e. dosimeter readings, evaluated inH_p(10) for estimation of radiation risk; however, the International Commission on Radiological Protection does not recommend the use of effective doses for epidemiological evaluation and instead recommends the use of organ-absorbed doses for assessing cancer risk. Recently, the J-EPISODE has developed a conversion factor that can convert dosimeter readings to organ-absorbed doses following, in principle, the approach adopted by the International Agency for Research on Cancer 15-Country Collaborative Study. The approach was modified based on recent dosimeter usage practices and the Japanese physique. The aim of this study was to reanalyse the excess relative risk (ERR) of cancer mortality for the J-EPISODE using the previous analysis method but substituting the organ-absorbed dose for the recorded dose to confirm the adaptability and relevance of organ-absorbed doses for the J-EPISODE. The organ-absorbed doses from 1957 to 2010 were reconstructed for the whole cohort. The cancer mortality risk was reanalysed with Poisson regression methods, first by comparing the ERR/Gy for all cancers excluding leukaemia with the risk after excluding lung cancer for the whole cohort of 204 103 participants. In the whole cohort, all cancers excluding leukaemia, lung cancer and non-Hodgkin's lymphoma had statistically significant positive ERR/Gy estimates; leukaemia excluding chronic lymphocytic leukaemia had negative but not statistically significant estimates. Gallbladder cancer and pancreatic cancer showed statistically significant negative. Then, a subcohort of 71 733 respondents was selected based on lifestyle surveys with data on qualitative smoking status as well as quantitative smoking information on pack-years. Pack-years for current smokers and former smokers and years since the cessation of smoking for former smokers were used for the smoking-adjusted model. The most important feature of the J-EPISODE revealed to date was a decreasing tendency of the ERR/Sv by the smoking adjustment. For almost all causes of death such as lung cancer and stomach cancer, the estimated ERR/Gy decreased by the smoking adjustment, although those for the colon, prostate and kidney and other urinary organs were almost the same after the adjustment. This tendency remained unchanged even when using the organ-absorbed dose, indicating the appropriateness of using organ-absorbed doses for further risk analysis. At the same time, it indicated that confounding by smoking seriously biased the radiation risk estimates in the J-EPISODE and thus should be accounted even if organ dose is used.

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.

Risk of cancer associated with low-dose radiation exposure: comparison of results between the INWORKS nuclear workers study and the A-bomb survivors study

The Life Span Study (LSS) of Japanese atomic bomb survivors has served as the primary basis for estimates of radiation-related disease risks that inform radiation protection standards. The long-term follow-up of radiation-monitored nuclear workers provides estimates of radiation-cancer associations that complement findings from the LSS. Here, a comparison of radiation-cancer mortality risk estimates derived from the LSS and INWORKS, a large international nuclear worker study, is presented. Restrictions were made, so that the two study populations were similar with respect to ages and periods of exposure, leading to selection of 45,625 A-bomb survivors and 259,350 nuclear workers. For solid cancer, excess relative rates (ERR) per gray (Gy) were 0.28 (90% CI 0.18; 0.38) in the LSS, and 0.29 (90% CI 0.07; 0.53) in INWORKS. A joint analysis of the data allowed for a formal assessment of heterogeneity of the ERR per Gy across the two studies (P = 0.909), with minimal evidence of curvature or of a modifying effect of attained age, age at exposure, or sex in either study. There was evidence in both cohorts of modification of the excess absolute risk (EAR) of solid cancer by attained age, with a trend of increasing EAR per Gy with attained age. For leukemia, under a simple linear model, the ERR per Gy was 2.75 (90% CI 1.73; 4.21) in the LSS and 3.15 (90% CI 1.12; 5.72) in INWORKS, with evidence of curvature in the association across the range of dose observed in the LSS but not in INWORKS; the EAR per Gy was 3.54 (90% CI 2.30; 5.05) in the LSS and 2.03 (90% CI 0.36; 4.07) in INWORKS. These findings from different study populations may help understanding of radiation risks, with INWORKS contributing information derived from cohorts of workers with protracted low dose-rate exposures.

Assessment of Residual Radioactivity by a Comprehensive Wireless, Wearable Device in Thyroid Cancer Patients Undergoing Radionuclide Therapy and Comparison With the Results of a Home Device: A Feasibility Study

Objective: To investigate the feasibility of using a wireless wearable device (WD) in differentiated thyroid cancer (DTC) patients undergoing radionuclide therapy with I-131 (RAI) and protected hospitalization, this study compared the measurements of residual radioactivity obtained with those registered by a permanent environmental home device (HD). Methods: Twenty consecutive patients undergoing RAI hospitalized in restricted, controlled areas were enrolled. The patients underwent comprehensive monitoring of vital/nonvital parameters. We obtained 45580± 13 measurements from the WD, detecting the residual radioactivity for each patient during approximately 56 hours of hospitalization, collecting data 53 times per hour. The samples, collected during daily activities, were averaged every two hours, and the results correlated with those from the HD. Bland-Altman analysis was also used to evaluate the agreement between the two techniques. Results: A significant relationship between the WD and HD was observed (r = 0.96, p < 0.0001). Bland-Altman analysis recognized the agreement between measurements by the WD and HD. The mean value at the end of the first day of hospitalization was 80.81 microSv/h and 60.77 microSv/h (p = ns for WD and HD), whereas those at the end of the second day were 47.08 and 24.96 (p = ns). In the generalized linear model (GLM), a similar trend in performance across time was found with the two techniques. Conclusion: This study demonstrates good agreement between the residual radioactivity measures estimated by the WD and HD modalities, rendering them interchangeable. This approach will allow both the optimization of medical staff exposure and safer patient discharge. Abbreviations: wireless device (WD); differentiated thyroid cancer (DTC); radionuclide therapy with I-131 (RAI); home device (HD); generalized linear model (GLM).

Meta-analysis of published excess relative risk estimates

A meta-analytic summary effect estimate often is calculated as an inverse-variance-weighted average of study-specific estimates of association. The variances of published estimates of association often are derived from their associated confidence intervals under assumptions typical of Wald-type statistics, such as normality of the parameter. However, in some research areas, such as radiation epidemiology, epidemiological results typically are obtained by fitting linear relative risk models, and associated likelihood-based confidence intervals are often asymmetric; consequently, reasonable estimates of variances associated with study-specific estimates of association may be difficult to infer from the standard approach based on the assumption of a Wald-type interval. Here, a novel method is described for meta-analysis of published results from linear relative risk models that uses a parametric transformation of published results to improve on the normal approximation used to assess confidence intervals. Using simulations, it is illustrated that the meta-analytic summary obtained using the proposed approach yields less biased summary estimates, with better confidence interval coverage, than the summary obtained using the more classical approach to meta-analysis. The proposed approach is illustrated using a previously published example of meta-analysis of epidemiological findings regarding circulatory disease following exposure to low-level ionizing radiation.

The Risk of Cancer from CT Scans and Other Sources of Low-Dose Radiation: A Critical Appraisal of Methodologic Quality

INTRODUCTION

Concern exists that radiation exposure from computerized tomography (CT) will cause thousands of malignancies. Other experts share the same perspective regarding the risk from additional sources of low-dose ionizing radiation, such as the releases from Three Mile Island (1979; Pennsylvania USA) and Fukushima (2011; Okuma, Fukushima Prefecture, Japan) nuclear power plant disasters. If this premise is false, the fear of cancer leading patients and physicians to avoid CT scans and disaster responders to initiate forced evacuations is unfounded.

STUDY OBJECTIVE

This investigation provides a quantitative evaluation of the methodologic quality of studies to determine the evidentiary strength supporting or refuting a causal relationship between low-dose radiation and cancer. It will assess the number of higher quality studies that support or question the role of low-dose radiation in oncogenesis.

METHODS

This investigation is a systematic, methodologic review of articles published from 1975-2017 examining cancer risk from external low-dose x-ray and gamma radiation, defined as less than 200 millisievert (mSv). Following the PRISMA guidelines, the authors performed a search of the PubMed, Cochrane, Scopus, and Web of Science databases. Methodologies of selected articles were scored using the Newcastle Ottawa Scale (NOS) and a tool identifying 11 lower quality indicators. Manuscript methodologies were ranked as higher quality if they scored no lower than seven out of nine on the NOS and contained no more than two lower quality indicators. Investigators then characterized articles as supporting or not supporting a causal relationship between low-dose radiation and cancer.

RESULTS

Investigators identified 4,382 articles for initial review. A total of 62 articles met all inclusion/exclusion criteria and were evaluated in this study. Quantitative evaluation of the manuscripts' methodologic strengths found 25 studies met higher quality criteria while 37 studies met lower quality criteria. Of the 25 studies with higher quality methods, 21 out of 25 did not support cancer induction by low-dose radiation (P = .0003).

CONCLUSIONS

A clear preponderance of articles with higher quality methods found no increased risk of cancer from low-dose radiation. The evidence suggests that exposure to multiple CT scans and other sources of low-dose radiation with a cumulative dose up to 100 mSv (approximately 10 scans), and possibly as high as 200 mSv (approximately 20 scans), does not increase cancer risk.

Outcome Assessment in Epidemiological Studies of Low-Dose Radiation Exposure and Cancer Risks: Sources, Level of Ascertainment, and Misclassification

BACKGROUND

Outcome assessment problems and errors that could lead to biased risk estimates in low-dose radiation epidemiological studies of cancer risks have not been systematically evaluated.

METHODS

Incidence or mortality risks for all cancers or all solid cancers combined and for leukemia were examined in 26 studies published in 2006-2017 involving low-dose (mean dose ≤100 mGy) radiation from environmental, medical, or occupational sources. We evaluated the impact of loss to follow-up, under- or overascertainment, outcome misclassification, and changing classifications occurring similarly or differentially across radiation dose levels.

RESULTS

Loss to follow-up was not reported in 62% of studies, but when reported it was generally small. Only one study critically evaluated the completeness of the sources of vital status. Underascertainment of cancers ("false negatives") was a potential shortcoming for cohorts that could not be linked with high-quality population-based registries, particularly during early years of exposure in five studies, in two lacking complete residential history, and in one with substantial emigration. False positives may have occurred as a result of cancer ascertainment from self- or next-of-kin report in three studies or from enhanced medical surveillance of exposed patients that could lead to detection bias (eg, reporting precancer lesions as physician-diagnosed cancer) in one study. Most pediatric but few adult leukemia studies used expert hematopathology review or current classifications. Only a few studies recoded solid cancers to the latest International Classification of Diseases or International Classification of Diseases for Oncology codes. These outcome assessment shortcomings were generally nondifferential in relation to radiation exposure level except possibly in four studies.

CONCLUSION

The majority of studies lacked information to enable comprehensive evaluation of all major sources of outcome assessment errors, although reported data suggested that the outcome assessment limitations generally had little effect on risk or biased estimates towards the null except possibly in four studies.

Risk of stomach cancer incidence in a cohort of Mayak PA workers occupationally exposed to ionizing radiation

Stomach cancer is a widespread health condition associated with environmental and genetic factors. Contribution of ionizing radiation to stomach cancer etiology is not sufficiently studied. This study was aimed to assess an association of the stomach cancer incidence risk with doses from occupational radiation exposure in a cohort of workers hired at main Mayak production association facilities in 1948–1982 taking into account non-radiation factors including digestive disorders. The study cohort comprised 22,377 individuals and by 31.12.2013 343 stomach cancer diagnoses had been reported among the cohort members. Occupational stomach absorbed doses were provided by the Mayak Worker Dosimetry System– 2008 (MWDS–2008) for external gamma ray exposure and by the Mayak Worker Dosimetry System– 2013 (MWDS–2013) for internal exposure to plutonium. Excess relative risks (ERR) per Gy for stomach cancer were estimated using the Poisson’s regression. Analyses were run using the AMFIT module of the EPICURE software. The stomach cancer incidence risk in the study cohort was found to be significantly associated with the stomach absorbed dose of gamma rays: ERR/Gy = 0.19 (95% CI: 0.01, 0.44) with a 0 year lag, and ERR/Gy = 0.20 (95% CI: 0.01, 0.45) with a 5 year lag. To estimate the baseline risk, sex, attained age, smoking status and alcohol consumption, chronic diseases (peptic ulcer, gastritis and duodenitis) were taken into account. No modifications of the radiogenic risk by non-radiation factors were found in the study worker cohort. No association of the stomach cancer incidence risk with internal exposure to incorporated plutonium was observed.

Dose limits for occupational exposure to ionising radiation and genotoxic carcinogens: a German perspective

This paper summarises the view of the German Commission on Radiological Protection ("Strahlenschutzkommission", SSK) on the rationale behind the currently valid dose limits and dose constraints for workers recommended by the International Commission on Radiological Protection (ICRP). The paper includes a discussion of the reasoning behind current dose limits followed by a discussion of the detriment used by ICRP as a measure for stochastic health effects. Studies on radiation-induced cancer are reviewed because this endpoint represents the most important contribution to detriment. Recent findings on radiation-induced circulatory disease that are currently not included in detriment calculation are also reviewed. It appeared that for detriment calculations the contribution of circulatory diseases plays only a secondary role, although the uncertainties involved in their risk estimates are considerable. These discussions are complemented by a review of the procedures currently in use in Germany, or in discussion elsewhere, to define limits for genotoxic carcinogens. To put these concepts in perspective, actual occupational radiation exposures are exemplified with data from Germany, for the year 2012, and regulations in Germany are compared to the recommendations issued by ICRP. Conclusions include, among others, considerations on radiation protection concepts currently in use and recommendations of the SSK on the limitation of annual effective dose and effective dose cumulated over a whole working life.

Risk of Leukemia Associated with Protracted Low-Dose Radiation Exposure: Updated Results from the National Registry for Radiation Workers Study

While the link between risk of leukemia and acute radiation exposure is well established for large doses received acutely, uncertainty remains around the translation of these risk estimates to occupational exposure scenarios where the doses are low and accumulated over time, possibly over many years. We present leukemia incidence and mortality radiation risk estimates derived from the National Registry for Radiation Workers, which is a large cohort of occupationally exposed workers from the United Kingdom (UK). The cohort comprised 173,081 workers from the UK who were monitored for occupational exposure to radiation. The cohort was followed for a total of 5.3 million person-years and the incidence and mortality due to leukemia was identified through to the end of follow-up in 2011. Poisson regression was used to investigate the relationship between cumulative radiation dose and leukemia mortality and incidence rates using excess relative risk (ERR) and excess additive risk (EAR) models. The results of this work showed a collective dose of 4,414 person-Sv accumulated by the cohort with an average cumulative dose of 25.5 mSv. Among male workers both the ERR and EAR models showed evidence of increased leukemia risk (excluding chronic lymphatic leukemia) associated with increasing cumulative dose. The ERR was 1.38 per Sv (90% CI: 0.04; 3.24) and EAR was 1.33 per 10,000 person-year-Sv (90% CI: 0.04; 2.89) when a linear model was used. These excess risks were driven by increased risks for chronic myeloid leukemia [ERR/Sv = 6.77 (90% CI: 2.14; 15.44)]. In conclusion, this study provides further evidence that leukemia risks may be increased by low-dose and protracted external radiation exposure. The risks are generally consistent with those observed in the atomic bomb survivor studies, as well as with risk coefficients on which international radiation safety standards, including the dose limits and constraints used to control exposures, are based.

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.

THE SPECTRUM OF TP53, SF3B1, AND NOTCH1 MUTATIONS IN CHRONIC LYMPHOCYTIC LEUKEMIA PATIENTS EXPOSED TO IONIZING RADIATION DUE TO THE CHORNOBYL NPP ACCIDENT

OBJECTIVE

to analyze TP53, NOTCH1 and SF3B1 mutations in chronic lymphocytic leukemia (CLL) patients, sufferersof Chornobyl NPP accident to clarify the possible relationship between ionizing radiation (IR) and CLL.

METHODS

Mutations of TP53, NOTCH1, and SF3B1 genes were studied by direct sequencing in the main group of 106 CLLpatients exposed to IR due to Chornobyl NPP accident and in the control group of 130 IR non-exposed CLL patients.

RESULTS

We found TP53 and SF3B1 mutations with similar incidence in both groups - 11.3 % and 10.0 % in the maingroup, and 12.7 % and 11.5 % in the control group, respectively. In contrast, the frequency of NOTCH1 mutationswas lower in IR-exposed patients (6.7 % vs 17.7 %; p = 0.012). TP53 mutations were seen with equal frequency amongmutated (11.1 %) and unmutated (11.8 %) immunoglobulin heavy-chain variable gene (IGHV) cases in IR-exposedCLL patients, while the tendency to prevalence of TP53 mutations in unmutated compared with mutated IGHV caseswas found in the control group (14.1 % and 5.6 %, correspondingly; p = 0.178). In IR-exposed group SF3B1 muta-tions were combined with mutations in TP53 almost in half of detected cases. In opposite, in the control group therewas mutual exclusivity between SF3B1 and TP53 lesions (p = 0.001). Among IR-exposed CLL patients we found two dif-ferent cases with identical rare mutation of TP53 gene - c.665C>T substitution (Pro222Leu). This substitution is verylikely to represent inherited TP53 mutation, which may influence CLL development under IR exposure.

CONCLUSION

Our preliminary data suggest that TP53 abnormalities are involved in CLL development in subjectsexposed at the Chornobyl accident and also a possible connection between inherited sensitivity to ionizing radia-tion caused by mutation in TP53, radiation and CLL development.

Effect of age-related baseline risk on radiation dose response for coronary heart disease

We attempted to estimate the mortality risk of radiation-associated coronary heart disease (CHD) by using a model in which radiation was assumed to participate in the atherosclerotic process jointly with ageing. Model parameters were determined by fitting the Life Span Study data of atomic bomb survivors. According to the model, the excess relative risk (ERR) varies depending on the baseline risk; when applied to the death statistics of Japan and the USA, the estimated ERR was consistently higher in the Japanese population. The absolute risk showed an opposite trend, such that the estimated lifetime attributable risk was approximately two times higher in the US population. Excess cases were expected to appear in old age almost synchronously with spontaneous cases; in contrast, the risk is practically unnoticeable for those young to middle aged. Our model suggests that the radiation dose-response curve for CHD, as well as the latency in epidemiological studies, could be modified by the baseline risk.

Health Impacts of Low-Dose Ionizing Radiation: Current Scientific Debates and Regulatory Issues

Health impacts of low-dose ionizing radiation are significant in important fields such as X-ray imaging, radiation therapy, nuclear power, and others. However, all existing and potential applications are currently challenged by public concerns and regulatory restrictions. We aimed to assess the validity of the linear no-threshold (LNT) model of radiation damage, which is the basis of current regulation, and to assess the justification for this regulation. We have conducted an extensive search in PubMed. Special attention has been given to papers cited in comprehensive reviews of the United States (2006) and French (2005) Academies of Sciences and in the United Nations Scientific Committee on Atomic Radiation 2016 report. Epidemiological data provide essentially no evidence for detrimental health effects below 100 mSv, and several studies suggest beneficial (hormetic) effects. Equally significant, many studies with in vitro and in animal models demonstrate that several mechanisms initiated by low-dose radiation have beneficial effects. Overall, although probably not yet proven to be untrue, LNT has certainly not been proven to be true. At this point, taking into account the high price tag (in both economic and human terms) borne by the LNT-inspired regulation, there is little doubt that the present regulatory burden should be reduced.

Probability Distribution of Dose and Dose-Rate Effectiveness Factor for use in Estimating Risks of Solid Cancers From Exposure to Low-Let Radiation

This paper presents an analysis to develop a subjective state-of-knowledge probability distribution of a dose and dose-rate effectiveness factor for use in estimating risks of solid cancers from exposure to low linear energy transfer radiation (photons or electrons) whenever linear dose responses from acute and chronic exposure are assumed. A dose and dose-rate effectiveness factor represents an assumption that the risk of a solid cancer per Gy at low acute doses or low dose rates of low linear energy transfer radiation, RL, differs from the risk per Gy at higher acute doses, RH; RL is estimated as RH divided by a dose and dose-rate effectiveness factor, where RH is estimated from analyses of dose responses in Japanese atomic-bomb survivors. A probability distribution to represent uncertainty in a dose and dose-rate effectiveness factor for solid cancers was developed from analyses of epidemiologic data on risks of incidence or mortality from all solid cancers as a group or all cancers excluding leukemias, including (1) analyses of possible nonlinearities in dose responses in atomic-bomb survivors, which give estimates of a low-dose effectiveness factor, and (2) comparisons of risks in radiation workers or members of the public from chronic exposure to low linear energy transfer radiation at low dose rates with risks in atomic-bomb survivors, which give estimates of a dose-rate effectiveness factor. Probability distributions of uncertain low-dose effectiveness factors and dose-rate effectiveness factors for solid cancer incidence and mortality were combined using assumptions about the relative weight that should be assigned to each estimate to represent its relevance to estimation of a dose and dose-rate effectiveness factor. The probability distribution of a dose and dose-rate effectiveness factor for solid cancers developed in this study has a median (50th percentile) and 90% subjective confidence interval of 1.3 (0.47, 3.6). The harmonic mean is 1.1, which implies that the arithmetic mean of an uncertain estimate of the risk of a solid cancer per Gy at low acute doses or low dose rates of low linear energy transfer radiation is only about 10% less than the mean risk per Gy at higher acute doses. Data were also evaluated to define a low acute dose or low dose rate of low linear energy transfer radiation, i.e., a dose or dose rate below which a dose and dose-rate effectiveness factor should be applied in estimating risks of solid cancers.

Assessing the health effects associated with occupational radiation exposure in Korean radiation workers: protocol for a prospective cohort study

INTRODUCTION

The cancer risk of radiation exposure in the moderate-to-high dose range has been well established. However, the risk remains unclear at low-dose ranges with protracted low-dose rate exposure, which is typical of occupational exposure. Several epidemiological studies of Korean radiation workers have been conducted, but the data were analysed retrospectively in most cases. Moreover, groups with relatively high exposure, such as industrial radiographers, have been neglected. Therefore, we have launched a prospective cohort study of all Korean radiation workers to assess the health effects associated with occupational radiation exposure.

METHODS AND ANALYSIS

Approximately 42 000 Korean radiation workers registered with the Nuclear Safety and Security Commission from 2016 to 2017 are the initial target population of this study. Cohort participants are to be enrolled through a nationwide self-administered questionnaire survey between 24 May 2016 and 30 June 2017. As of 31 March 2017, 22 982 workers are enrolled in the study corresponding to a response rate of 75%. This enrolment will be continued at 5-year intervals to update information on existing study participants and recruit newly hired workers. Survey data will be linked with the national dose registry, the national cancer registry, the national vital statistics registry and national health insurance data via personal identification numbers. Age-specific and sex-specific standardised incidence and mortality ratios will be calculated for overall comparisons of cancer risk. For dose-response assessment, excess relative risk (per Gy) and excess absolute risk (per Gy) will be estimated with adjustments for birth year and potential confounders, such as lifestyle factors and socioeconomic status.

ETHICS AND DISSEMINATION

This study has received ethical approval from the institutional review board of the Korea Institute of Radiological and Medical Sciences (IRB No. K-1603-002-034). All participants provided written informed consent prior to enrolment. The findings of the study will be disseminated through scientific peer-reviewed journals and be provided to the public, including radiation workers, via the study website (http://www.rhs.kr/) and onsite radiation safety education.

Low-dose ionizing radiation increases the mortality risk of solid cancers in nuclear industry workers: A meta-analysis

Low-dose ionizing radiation (LDIR) may increase the mortality of solid cancers in nuclear industry workers, but only few individual cohort studies exist, and the available reports have low statistical power. The aim of the present study was to focus on solid cancer mortality risk from LDIR in the nuclear industry using standard mortality ratios (SMRs) and 95% confidence intervals. A systematic literature search through the PubMed and Embase databases identified 27 studies relevant to this meta-analysis. There was statistical significance for total, solid and lung cancers, with meta-SMR values of 0.88, 0.80, and 0.89, respectively. There was evidence of stochastic effects by IR, but more definitive conclusions require additional analyses using standardized protocols to determine whether LDIR increases the risk of solid cancer-related mortality.

An Assessment of Radiation-Associated Risks of Mortality from Circulatory Disease in the Cohorts of Mayak and Sellafield Nuclear Workers

Mortality from circulatory disease (CD), ischemic heart disease (IHD) and cerebrovascular disease (CeVD) was investigated in relationship to cumulative doses of external gamma radiation and internal alpha radiation to the liver from deposited plutonium over long follow-up periods in two large cohorts of nuclear workers: the Russian Mayak Worker Cohort (MWC) and the UK Sellafield Worker Cohort (SWC). The MWC comprised 22,374 workers (74.6% males) with 5,123 CD deaths registered during 842,538 person-years of follow-up, while the SWC comprised 23,443 workers (87.8% males) with 2,322 CD deaths registered during 602,311 person-years of follow-up. Dose estimates for external gamma radiation and internal alpha radiation to the liver were calculated via a common methodology, in accordance with an agreed protocol. The mean cumulative external H_p(10) dose was 0.52 Sv for the MWC and 0.07 Sv for the SWC, while the mean cumulative internal dose was 0.19 Gy for the MWC and 0.01 Gy for the SWC. Categorical relative risks (RR) and excess relative risks (ERR) per unit dose were estimated for each cohort and for the pooled cohort when appropriate. The dose responses for CD, IHD and CeVD in relationship to internal alpha-particle dose did not differ significantly from the null for either the MWC, the SWC or the pooled plutonium worker cohort. The ERR/Sv estimates in relationship to external exposure were significantly raised for both cohorts (marginally so for the MWC) for CD and IHD (but not for CeVD), but differed significantly between the two cohorts, the estimate for the SWC being approximately ten times greater than that for the MWC. Examination of the ERR/Sv estimates for two periods of first employment at the two facilities revealed that the significant heterogeneity was confined to the earlier sub-cohorts, and that the estimates for the later sub-cohorts were compatible. The two sub-cohorts for the later first-employment periods were pooled, producing risk estimates that were raised, but not significantly so: ERR/Sv for CD, IHD and CeVD of 0.22 (95% CI: -0.01, 0.49), 0.22 (95% CI: -0.06, 0.57) and 0.24 (95% CI: -0.17, 0.80), respectively. The reasons for the complex pattern of results found in this study are unclear. Among potential explanations are the influence of differences in background CD mortality rates, an effect of other occupational factors, substantial uncertainties in doses, particularly during earlier periods of operations, as well as confounding and/or modifying factors that were not taken into account in the current analysis.

Radiation-related occupational cancer and its recognition criteria in South Korea

Ionizing radiation is a well-known carcinogen, and is listed as one carcinogenic agent of occupational cancer. Given the increase in the number of workers exposed to radiation, as well as the increase in concern regarding occupational cancer, the number of radiation-related occupational cancer claims is expected to increase. Unlike exposure assessment of other carcinogenic agents in the workplace, such as asbestos and benzene, radiation exposure is usually assessed on an individual basis with personal dosimeters, which makes it feasible to assess whether a worker’s cancer occurrence is associated with their individual exposure. However, given the absence of a threshold dose for cancer initiation, it remains difficult to identify radiation exposure as the root cause of occupational cancer. Moreover, the association between cancer and radiation exposure in the workplace has not been clearly established due to a lack of scientific evidence. Therefore, criteria for the recognition of radiation-related occupational cancer should be carefully reviewed and updated with new scientific evidence and social consensus. The current criteria in Korea are valid in terms of eligible radiogenic cancer sites, adequate latent period, assessment of radiation exposure, and probability of causation. However, reducing uncertainty with respect to the determination of causation between exposure and cancer and developing more specific criteria that considers mixed exposure to radiation and other carcinogenic agents remains an important open question.

Site-specific Solid Cancer Mortality After Exposure to Ionizing Radiation: A Cohort Study of Workers (INWORKS)

BACKGROUND

There is considerable scientific interest in associations between protracted low-dose exposure to ionizing radiation and the occurrence of specific types of cancer.

METHODS

Associations between ionizing radiation and site-specific solid cancer mortality were examined among 308,297 nuclear workers employed in France, the United Kingdom, and the United States. Workers were monitored for external radiation exposure and follow-up encompassed 8.2 million person-years. Radiation-mortality associations were estimated using a maximum-likelihood method and using a Markov chain Monte Carlo method, the latter used to fit a hierarchical regression model to stabilize estimates of association.

RESULTS

The analysis included 17,957 deaths attributable to solid cancer, the most common being lung, prostate, and colon cancer. Using a maximum-likelihood method to quantify associations between radiation dose- and site-specific cancer, we obtained positive point estimates for oral, esophagus, stomach, colon, rectum, pancreas, peritoneum, larynx, lung, pleura, bone and connective tissue, skin, ovary, testis, and thyroid cancer; in addition, we obtained negative point estimates for cancer of the liver and gallbladder, prostate, bladder, kidney, and brain. Most of these estimated coefficients exhibited substantial imprecision. Employing a hierarchical model for stabilization had little impact on the estimated associations for the most commonly observed outcomes, but for less frequent cancer types, the stabilized estimates tended to take less extreme values and have greater precision than estimates obtained without such stabilization.

CONCLUSIONS

The results provide further evidence regarding associations between low-dose radiation exposure and cancer.

Impact of considering non-occupational radiation exposure on the association between occupational dose and solid cancer among French nuclear workers

OBJECTIVES

The French nuclear worker cohort allows for the assessment of cancer risk associated with occupational radiation exposure, but workers are also exposed to medical and environmental radiation which can be of the same order of magnitude. This study aims to examine the impact of non-occupational radiation exposures on the dose-risk analysis between occupational radiation exposure and cancer mortality.

METHODS

The cohort included workers employed before 1995 for at least one year by CEA, AREVA NC or EDF and badge-monitored for external radiation exposure. Monitoring results were used to calculate occupational individual doses. Scenarios of work-related X-ray and environmental exposures were simulated. Poisson regression was used to quantify associations between occupational exposure and cancer mortality adjusting for non-occupational radiation exposure.

RESULTS

The mean cumulative dose of external occupational radiation was 18.4 mSv among 59 004 workers. Depending on the hypotheses made, the mean cumulative work-related X-ray dose varied between 3.1 and 9.2 mSv and the mean cumulative environmental dose was around 130 mSv. The unadjusted excess relative rate of cancer per Sievert (ERR/Sv) was 0.34 (90% CI -0.44 to 1.24). Adjusting for environmental radiation exposure did not substantially modify this risk coefficient, but it was attenuated by medical exposure (ERR/Sv point estimate between 0.15 and 0.23).

CONCLUSIONS

Occupational radiation risk estimates were lower when adjusted for work-related X-ray exposures. Environmental exposures had a very slight impact on the occupational exposure risk estimates. In any scenario of non-occupational exposure considered, a positive but insignificant excess cancer risk associated with occupational exposure was observed.

Radiation exposure and lung disease in today's nuclear world

PURPOSE OF REVIEW

Ionizing radiation poses important health risks. The per capita annual dose rate has increased in the United States and there is increasing concern for the risks posed by low-dose occupational exposure among workers in nuclear industries and healthcare. Recent nuclear accidents and concern for terrorism have heightened concern for catastrophic, high-dose ionizing radiation exposure. This review will highlight recent research into the risks to lung health posed by ionizing radiation exposure and into potential treatments.

RECENT FINDINGS

Angiotensin-converting enzyme inhibitors and some antioxidants have shown promise as mitigators, to decrease pneumonitis and fibrosis when given after exposure. Studies of survivors of nuclear catastrophes have shown increased risk for lung cancer, especially in nonsmokers. There is evidence for increased lung cancer risk in industrial radiation workers, especially those who process plutonium and may inhale radioactive particles. There does not seem to be an increased risk of lung cancer in healthcare workers who perform fluoroscopic procedures.

SUMMARY

High-dose ionizing radiation exposure causes pneumonitis and fibrosis, and more research is needed to develop mitigators to improve outcomes in nuclear catastrophes. Long-term, low-dose occupational radiation may increase lung cancer risk. More research to better define this risk could lead to improved safety protocols and screening programs.

Mortality from Circulatory Diseases and other Non-Cancer Outcomes among Nuclear Workers in France, the United Kingdom and the United States (INWORKS)

Positive associations between external radiation dose and non-cancer mortality have been found in a number of published studies, primarily of populations exposed to high-dose, high-dose-rate ionizing radiation. The goal of this study was to determine whether external radiation dose was associated with non-cancer mortality in a large pooled cohort of nuclear workers exposed to low-dose radiation accumulated at low dose rates. The cohort comprised 308,297 workers from France, United Kingdom and United States. The average cumulative equivalent dose at a tissue depth of 10 mm [Hp(10)] was 25.2 mSv. In total, 22% of the cohort were deceased by the end of follow-up, with 46,029 deaths attributed to non-cancer outcomes, including 27,848 deaths attributed to circulatory diseases. Poisson regression was used to investigate the relationship between cumulative radiation dose and non-cancer mortality rates. A statistically significant association between radiation dose and all non-cancer causes of death was observed [excess relative risk per sievert (ERR/Sv) = 0.19; 90% CI: 0.07, 0.30]. This was largely driven by the association between radiation dose and mortality due to circulatory diseases (ERR/Sv = 0.22; 90% CI: 0.08, 0.37), with slightly smaller positive, but nonsignificant, point estimates for mortality due to nonmalignant respiratory disease (ERR/Sv = 0.13; 90% CI: -0.17, 0.47) and digestive disease (ERR/Sv = 0.11; 90% CI: -0.36, 0.69). The point estimate for the association between radiation dose and deaths due to external causes of death was nonsignificantly negative (ERR = -0.12; 90% CI: <-0.60, 0.45). Within circulatory disease subtypes, associations with dose were observed for mortality due to cerebrovascular disease (ERR/Sv = 0.50; 90% CI: 0.12, 0.94) and mortality due to ischemic heart disease (ERR/Sv = 0.18; 90% CI: 0.004, 0.36). The estimates of associations between radiation dose and non-cancer mortality are generally consistent with those observed in atomic bomb survivor studies. The findings of this study could be interpreted as providing further evidence that non-cancer disease risks may be increased by external radiation exposure, particularly for ischemic heart disease and cerebrovascular disease. However, heterogeneity in the estimated ERR/Sv was observed, which warrants further investigation. Further follow-up of these cohorts, with the inclusion of internal exposure information and other potential confounders associated with lifestyle factors, may prove informative, as will further work on elucidating the biological mechanisms that might cause these non-cancer effects at low doses.

Examining temporal effects on cancer risk in the international nuclear workers' study

The paper continues the series of publications from the International Nuclear Workers Study cohort that comprises 308,297 workers from France, the United Kingdom and the United States, providing 8.2 million person-years of observation from a combined follow-up period (at earliest 1944 to at latest 2005). These workers' external radiation exposures were primarily to photons, resulting in an estimated average career absorbed dose to the colon of 17.4 milligray. The association between cumulative ionizing radiation dose and cancer mortality was evaluated in general relative risk models that describe modification of the excess relative risk (ERR) per gray (Gy) by time since exposure and age at exposure. Methods analogous to a nested-case control study using conditional logistic regression of sampled risks sets were used. Outcomes included: all solid cancers, lung cancer, leukemias excluding chronic lymphocytic, acute myeloid leukemia, chronic myeloid leukemia, multiple myeloma, Hodgkin lymphoma and non-Hodgkin lymphoma. Significant risk heterogeneity was evident in chronic myeloid leukemia with time since exposure, where we observed increased ERR per Gy estimates shortly after exposure (2-10 year) and again later (20-30 years). We observed delayed effects for acute myeloid leukemia although estimates were not statistically significant. Solid cancer excess risk was restricted to exposure at age 35+ years and also diminished for exposure 30 years prior to attained age. Persistent or late effects suggest additional follow-up may inform on lifetime risks. However, cautious interpretation of results is needed due to analytical limitations and a lack of confirmatory results from other studies.

Heart Disease Mortality in the Life Span Study, 1950-2008

Based on the findings from the Radiation Effects Research Foundation's studies of the cohort of Japanese atomic bomb survivors, it has been reported that total-body irradiation at 0.5-1.0 Gy could be responsible for increased rates of mortality from broad-based categories of cardiovascular disease (CVD), i.e., stroke and heart disease. However, CVD consists of various subtypes that have potentially different radiation dose responses, as well as subtype-specific risks that have not been fully evaluated. Potential problems with changes in the coding rules for the International Classification of Diseases (ICD) and the underlying causes and trends in CVD mortality in Japan also need to be considered. The goal of this study was to clarify the radiation risk of subtype-specific heart disease over different time periods. Radiation dose response was examined for mortality from several heart disease subtypes in 86,600 members of the Life Span Study (LSS) cohort during 1950-2008. These subtypes included ischemic heart disease (IHD), valvular heart disease (VHD), hypertensive organ damage (HOD) and heart failure (HF). Individual radiation doses ranged between 0 and 4 Gy. In addition to analyses for the total period, we examined specific periods, 1950-1968, 1969-1980, 1981-1994 and 1995-2008, corresponding to major developments in medical technologies and ICD code revisions. We observed significant positive associations between radiation dose and mortality from heart disease overall in 1950-2008 [excess relative risk or ERR/Gy (95% CI) = 0.14 (0.06, 0.22)]. Subtype-specific ERRs also positively increased with dose: 0.45 (0.13, 0.85) for VHD, 0.36 (0.10, 0.68) for HOD and 0.21 (0.07, 0.37) for HF, respectively. No significant departure from linearity was shown for the dose-response model. Although there was no evidence for a threshold in a model function, the lowest dose ranges with a statistically significant dose response were 0-0.7 Gy for heart disease overall and VHD, 0-1.5 Gy for HOD and 0-0.4 Gy for HF. No significant association between radiation exposure and IHD was observed in any model, although a quadratic model fit the best. The risk of HOD and rheumatic VHD increased significantly in the earliest periods [ERR/Gy = 0.59 (0.07, 1.32) and 1.34 (0.24, 3.16), respectively]. The risk of nonrheumatic VHD increased with calendar time and was significant in the latest period [ERR/Gy = 0.75 (0.02, 1.92)]. The risk of IHD, especially for myocardial infarction, tended to be elevated in the most recent period after 2001, where cautious interpretation is needed due to the uncertain validity of death diagnosis. Radiation risks of heart disease mortality in the LSS appeared to vary substantially among subtypes, indicating possible differences in radiation-induced pathogenesis. Trends in CVD rates in Japan during the long observation period may also impact risk analyses.

External radiation dose and cancer mortality among French nuclear workers: considering potential confounding by internal radiation exposure

OBJECTIVES

French nuclear workers have detailed records of their occupational exposure to external radiation that have been used to examine associations with subsequent cancer mortality. However, some workers were also exposed to internal contamination by radionuclides. This study aims to assess the potential for bias due to confounding by internal contamination of estimates of associations between external radiation exposure and cancer mortality.

METHODS

A cohort of 59,004 workers employed for at least 1 year between 1950 and 1994 by CEA (Commissariat à l'Energie Atomique), AREVA NC, or EDF (Electricité de France) and badge-monitored for external radiation exposure were followed through 2004 to assess vital status and cause of death. A flag based on a workstation-exposure matrix defined four levels of potential for internal contamination. Standardized mortality ratios were assessed for each level of the internal contamination indicator. Poisson regression was used to quantify associations between external radiation exposure and cancer mortality, adjusting for potential internal contamination.

RESULTS

For solid cancer, the mortality deficit tended to decrease as the levels of potential for internal contamination increased. For solid cancer and leukemia excluding chronic lymphocytic leukemia, adjusting the dose-response analysis on the internal contamination indicator did not markedly change the excess relative risk per Sievert of external radiation dose.

CONCLUSIONS

This study suggests that in this cohort, neglecting information on internal dosimetry while studying the association between external dose and cancer mortality does not generate a substantial bias. To investigate more specifically the health effects of internal contamination, an effort is underway to estimate organ doses due to internal contamination.

Cancer and non-cancer mortality among French uranium cycle workers: the TRACY cohort

OBJECTIVES

The health effects of internal contamination by radionuclides, and notably by uranium, are poorly characterised. New cohorts of uranium workers are needed to better examine these effects. This paper analyses for the first time the mortality profile of the French cohort of uranium cycle workers. It considers mortality from cancer and non-cancer causes.

METHODS

The cohort includes workers employed at least 6 months between 1958 and 2006 in French companies involved in the production of nuclear fuel. Vital status and causes of death were collected from French national registries. Workers were followed-up from 1 January 1968 to 31 December 2008. Standardised mortality ratios (SMRs) were computed based on mortality rates for the French general population.

RESULTS

The cohort includes 12,649 workers (88% men). The average length of follow-up is 27 years and the mean age at the end of the study is 60 years. Large mortality deficits are observed for non-cancer causes of death such as non-cancer respiratory diseases (SMR=0.51 (0.41 to 0.63)) and circulatory diseases (SMR=0.68 (0.62 to 0.74)). A mortality deficit of lower magnitude is also observed for all cancers combined (SMR (95% CI): 0.76 (0.71 to 0.81)). Pleural mesothelioma is elevated (SMR=2.04 (1.19 to 3.27)).

CONCLUSIONS

A healthy worker effect is observed in this new cohort of workers involved in the uranium cycle. Collection of individual information on internal uranium exposure as well as other risk factors is underway, to allow for the investigation of uranium-related risks.

Is the Linear No-Threshold Dose-Response Paradigm Still Necessary for the Assessment of Health Effects of Low Dose Radiation?

Inevitable human exposure to ionizing radiation from man-made sources has been increased with the proceeding of human civilization and consequently public concerns focus on the possible risk to human health. Moreover, Fukushima nuclear power plant accidents after the 2011 East-Japan earthquake and tsunami has brought the great fear and anxiety for the exposure of radiation at low levels, even much lower levels similar to natural background. Health effects of low dose radiation less than 100 mSv have been debated whether they are beneficial or detrimental because sample sizes were not large enough to allow epidemiological detection of excess effects and there was lack of consistency among the available experimental data. We have reviewed an extensive literature on the low dose radiation effects in both radiation biology and epidemiology, and highlighted some of the controversies therein. This article could provide a reasonable view of utilizing radiation for human life and responding to the public questions about radiation risk. In addition, it suggests the necessity of integrated studies of radiobiology and epidemiology at the national level in order to collect more systematic and profound information about health effects of low dose radiation.

Risk of cancer from occupational exposure to ionising radiation: retrospective cohort study of workers in France, the United Kingdom, and the United States (INWORKS)

STUDY QUESTION

Is protracted exposure to low doses of ionising radiation associated with an increased risk of solid cancer?

METHODS

In this cohort study, 308,297 workers in the nuclear industry from France, the United Kingdom, and the United States with detailed monitoring data for external exposure to ionising radiation were linked to death registries. Excess relative rate per Gy of radiation dose for mortality from cancer was estimated. Follow-up encompassed 8.2 million person years. Of 66,632 known deaths by the end of follow-up, 17,957 were due to solid cancers.

STUDY ANSWER AND LIMITATIONS

Results suggest a linear increase in the rate of cancer with increasing radiation exposure. The average cumulative colon dose estimated among exposed workers was 20.9 mGy (median 4.1 mGy). The estimated rate of mortality from all cancers excluding leukaemia increased with cumulative dose by 48% per Gy (90% confidence interval 20% to 79%), lagged by 10 years. Similar associations were seen for mortality from all solid cancers (47% (18% to 79%)), and within each country. The estimated association over the dose range of 0-100 mGy was similar in magnitude to that obtained over the entire dose range but less precise. Smoking and occupational asbestos exposure are potential confounders; however, exclusion of deaths from lung cancer and pleural cancer did not affect the estimated association. Despite substantial efforts to characterise the performance of the radiation dosimeters used, the possibility of measurement error remains.

WHAT THIS STUDY ADDS

The study provides a direct estimate of the association between protracted low dose exposure to ionising radiation and solid cancer mortality. Although high dose rate exposures are thought to be more dangerous than low dose rate exposures, the risk per unit of radiation dose for cancer among radiation workers was similar to estimates derived from studies of Japanese atomic bomb survivors. Quantifying the cancer risks associated with protracted radiation exposures can help strengthen the foundation for radiation protection standards.

FUNDING, COMPETING INTERESTS, DATA SHARING

Support from the US Centers for Disease Control and Prevention; Ministry of Health, Labour and Welfare of Japan; Institut de Radioprotection et de Sûreté Nucléaire; AREVA; Electricité de France; US National Institute for Occupational Safety and Health; US Department of Energy; and Public Health England. Data are maintained and kept at the International Agency for Research on Cancer.

Ischaemic heart disease incidence and mortality in an extended cohort of Mayak workers first employed in 1948-1982

OBJECTIVE

Incidence and mortality from ischaemic heart disease (IHD) was studied in an extended cohort of 22,377 workers first employed at the Mayak Production Association during 1948-82 and followed up to the end of 2008.

METHODS

Relative risks and excess relative risks per unit dose (ERR/Gy) were calculated based on the maximum likelihood using Epicure software (Hirosoft International Corporation, Seattle, WA). Dose estimates used in analyses were provided by an updated "Mayak Worker Dosimetry System-2008".

RESULTS

A significant increasing linear trend in IHD incidence with total dose from external γ-rays was observed after having adjusted for non-radiation factors and dose from internal radiation {ERR/Gy = 0.10 [95% confidence interval (CI): 0.04 to 0.17]}. The pure quadratic model provided a better fit of the data than did the linear one. No significant association of IHD mortality with total dose from external γ-rays after having adjusted for non-radiation factors and dose from internal alpha radiation was observed in the study cohort [ERR/Gy = 0.06 (95% CI: <0 to 0.15)]. A significant increasing linear trend was observed in IHD mortality with total absorbed dose from internal alpha radiation to the liver after having adjusted for non-radiation factors and dose from external γ-rays in both the whole cohort [ERR/Gy = 0.21 (95% CI: 0.01 to 0.58)] and the subcohort of workers exposed at alpha dose <1.00 Gy [ERR/Gy = 1.08 (95% CI: 0.34 to 2.15)]. No association of IHD incidence with total dose from internal alpha radiation to the liver was found in the whole cohort after having adjusted for non-radiation factors and external gamma dose [ERR/Gy = 0.02 (95% CI: not available to 0.10)]. Statistically significant dose effect was revealed in the subcohort of workers exposed to internal alpha radiation at dose to the liver <1.00 Gy [ERR/Gy = 0.44 (95% CI: 0.09 to 0.85)].

CONCLUSION

This study provides strong evidence of IHD incidence and mortality association with external γ-ray exposure and some evidence of IHD incidence and mortality association with internal alpha-radiation exposure.

ADVANCES IN KNOWLEDGE

It is the first time the validity of internal radiation dose estimates has been shown to affect the risk of IHD incidence.

Ionising radiation and risk of death from leukaemia and lymphoma in radiation-monitored workers (INWORKS): an international cohort study

BACKGROUND

There is much uncertainty about the risks of leukaemia and lymphoma after repeated or protracted low-dose radiation exposure typical of occupational, environmental, and diagnostic medical settings. We quantified associations between protracted low-dose radiation exposures and leukaemia, lymphoma, and multiple myeloma mortality among radiation-monitored adults employed in France, the UK, and the USA.

METHODS

We assembled a cohort of 308,297 radiation-monitored workers employed for at least 1 year by the Atomic Energy Commission, AREVA Nuclear Cycle, or the National Electricity Company in France, the Departments of Energy and Defence in the USA, and nuclear industry employers included in the National Registry for Radiation Workers in the UK. The cohort was followed up for a total of 8.22 million person-years. We ascertained deaths caused by leukaemia, lymphoma, and multiple myeloma. We used Poisson regression to quantify associations between estimated red bone marrow absorbed dose and leukaemia and lymphoma mortality.

FINDINGS

Doses were accrued at very low rates (mean 1.1 mGy per year, SD 2.6). The excess relative risk of leukaemia mortality (excluding chronic lymphocytic leukaemia) was 2.96 per Gy (90% CI 1.17-5.21; lagged 2 years), most notably because of an association between radiation dose and mortality from chronic myeloid leukaemia (excess relative risk per Gy 10.45, 90% CI 4.48-19.65).

INTERPRETATION

This study provides strong evidence of positive associations between protracted low-dose radiation exposure and leukaemia.

FUNDING

Centers for Disease Control and Prevention, Ministry of Health, Labour and Welfare of Japan, Institut de Radioprotection et de Sûreté Nucléaire, AREVA, Electricité de France, National Institute for Occupational Safety and Health, US Department of Energy, US Department of Health and Human Services, University of North Carolina, Public Health England.

Dose Estimation for a Study of Nuclear Workers in France, the United Kingdom and the United States of America: Methods for the International Nuclear Workers Study (INWORKS)

In the framework of the International Nuclear Workers Study conducted in France, the UK and the U.S. (INWORKS), updated and expanded methods were developed to convert recorded doses of ionizing radiation to estimates of organ doses or individual personal dose equivalent [H(p)(10)] for a total number of 308,297 workers, including 40,035 women. This approach accounts for differences in dosimeter response to predominant workplace energy and geometry of exposure and for the recently published ICRP report on dose coefficients for men and women separately. The overall mean annual individual personal dose equivalent, including zero doses, is 1.73 mSv [median = 0.42; interquartile range (IQR): 0.07, 1.59]. Associated individual organ doses were estimated. INWORKS includes workers who had potential for exposure to neutrons. Therefore, we analyzed neutron dosimetry data to identify workers potentially exposed to neutrons. We created a time-varying indicator for each worker, classifying them according to whether they had a positive recorded neutron dose and if so, whether their neutron dose ever exceeded 10% of their total external penetrating radiation dose. The number of workers flagged as being exposed to neutrons was 13% for the full cohort, with 15% of the cohort in France, 12% of the cohort in the UK and 14% in the U.S. We also used available information on in vivo and bioassay monitoring to identify workers with known depositions or suspected internal contaminations. As a result of this work, information is now available that will allow various types of sensitivity analyses.

Cerebrovascular Diseases in Workers at Mayak PA: The Difference in Radiation Risk between Incidence and Mortality

A detailed analysis of cerebrovascular diseases (CeVD) for the cohort of workers at Mayak Production Association (PA) is presented. This cohort is especially suitable for the analysis of radiation induced circulatory diseases, due to the detailed medical surveillance and information on several risk factors. The risk after external, typically protracted, gamma exposure is analysed, accounting for potential additional internal alpha exposure. Three different endpoints have been investigated: incidence and mortality from all cerebrovascular diseases and incidence of stroke. Particular emphasis was given to the form of the dose-response relationship and the time dependence of the radiation induced risk. Young attained age was observed to be an important, aggravating modifier of radiation risk for incidence of CeVD and stroke. For incidence of CeVD, our analysis supports a dose response sub-linear for low doses. Finally, the excess relative risk per dose was confirmed to be significantly higher for incidence of CeVD compared to CeVD mortality and incidence of stroke. Arguments are presented for this difference to be based on a true biological effect.