Analyses of combined mortality data on workers at the Hanford Site, Oak Ridge National Laboratory, and Rocky Flats Nuclear Weapons Plant

An important objective of studies of workers exposed occupationally to chronic low doses of ionizing radiation is to provide a direct assessment of health risks resulting from this exposure. This objective is most effectively accomplished by conducting combined analyses that allow evaluation of the totality of evidence from all study populations. In this paper, combined analyses of mortality in workers at the Hanford Site, Oak Ridge National Laboratory, and Rocky Flats Nuclear Weapons Plant are presented. These combined analyses provide no evidence of a correlation between radiation exposure and mortality from all cancer or from leukemia. Of 11 other specific types of cancer analyzed, multiple myeloma was the only cancer found to exhibit a statistically significant correlation with radiation exposure. Estimates of the excess risk of all cancer and of leukemia, based on the combined data, were negative. Upper confidence limits based on the combined data were lower than for any single population, and were similar to estimates obtained from recent analyses of A-bomb survivor data. These results strengthen support for the conclusion that estimates obtained through extrapolation from high-dose data do not seriously underestimate risks of low-dose exposure, but leave open the possibility that extrapolation may overestimate risks.     

Altitude, radiation, and mortality from cancer and heart disease

The variation in background radiation levels is an important source of information for estimating human risks associated with low-level exposure to ionizing radiation. Several studies conducted in the United States, correlating mortality rates for cancer with estimated background radiation levels, found an unexpected inverse relationship. Such results have been interpreted as suggesting that low levels of ionizing radiation may actually confer some benefit. An environmental factor strongly correlated with background radiation is altitude. Since there are important physiological adaptations associated with breathing thinner air, such changes may themselves influence risk. We therefore fit models that simultaneously incorporated altitude and background radiation as predictors of mortality. The negative correlations with background radiation seen for mortality from arteriosclerotic heart disease and cancers of the lung, the intestine, and the breast disappeared or became positive once altitude was included in the models. By contrast, the significant negative correlations with altitude persisted with adjustment for radiation. Interpretation of these results is problematic, but recent evidence implicating reactive forms of oxygen in carcinogenesis and atherosclerosis may be relevant. We conclude that the cancer correlational studies carried out in the United States using vital statistics data do not in themselves demonstrate a lack of carcinogenic effect of low radiation levels, and that reduced oxygen pressure of inspired air may be protective against certain causes of death.     

Mortality of employees of the Atomic Weapons Establishment, 1951-82.

A total of 22,552 workers employed by the Atomic Weapons Establishment between 1951 and 1982 were followed up for an average of 18.6 years. Of the 3115 who died, 865 (28%) died of cancer. Mortality was 23% lower than the national average for all causes of death and 18% lower for cancer. These low rates were consistent with the findings in other workforces in the nuclear industry and reflect, at least in part, the selection of healthy people to work in the industry and the disproportionate recruitment of people from the higher social classes. At some time during their employment 9389 (42%) of the workers were monitored for exposure to radiation, the average cumulative whole body exposure to external radiation being 7.8 mSv. Their mortality was generally similar to that of other employees, even when exposures were lagged by 10 years. The rate ratio after a 10 year lag in workers with a radiation record compared with other workers was 1.01 (95% confidence interval 0.92 to 1.10) for all causes of death and 1.06 (0.89 to 1.27) for all malignant neoplasms. The only significant differences were for prostatic cancer (rate ratio 2.23; 95% confidence interval 1.13 to 4.40) and for cancers of ill defined and secondary sites (rate ratio 2.37; 1.23 to 4.56). Cancers of lymphatic and haemopoietic tissues were notable for their low occurrence in the study population, with only four deaths from leukaemia and two from multiple myeloma in workers with a radiation record, 9.16 and 3.55 deaths respectively being expected on the basis of national rates. Among workers who had a radiation record 3742 (40%) were also monitored for possible internal exposure to plutonium, 3044 (32%) to uranium, 1562 (17%) to tritium, 638 (7%) to polonium, and 281 (3%) to actinium. In these workers mortality from malignant neoplasms as a whole was not increased, but after a 10 year lag death rates from prostatic and renal cancers were generally more than twice the national average, these excesses arising in a small group of workers monitored for exposure to multiple radionuclides. Though mortality from lung cancer in workers monitored for exposure to plutonium was below the national average, it was some two thirds higher than in other radiation workers, the excess being of borderline statistical significance. Mortality from malignant neoplasms as a whole showed a weak and non-significant increasing trend with increasing level of cumulative whole body exposure to external radiation. When the exposures were lagged by 10 years the trend became stronger and significant, the estimated increase in relative risk per 10 mSv being 7.6% (95% confidence interval 0.4% to 15.3%). This trend was confined almost entirely to workers who were also monitored for exposure to radionuclides (p<0.001), the main contributions coming from lung cancer and prostatic cancer. Exposures of the lung and prostate from internal sources of radiation were not quantified, except for the contribution from tritium. It was therefore not possible to assess the extent to which the associations were due to internally deposited radionuclides rather than external exposure. The finding for prostatic cancer taken in conjunction with the results of other studies suggest a specific occupational hazard in a small group of workers in the nuclear industry who had comparatively high exposures to external radiation and who were also monitored for internal exposure to multiple radionuclides. Research is needed to discover whether any of the radionuclides and other substances concerned are concentrated in the prostate. The occurrence of lung cancer in this workforce requires further investigation taking into account smoking habits and tissue doses from inhaled radionuclides.     

Mortality of workers at the Sellafield plant of British Nuclear Fuels.

The mortality of all 14,327 people who were known to have been employed at the Sellafield plant of British Nuclear Fuels at any time between the opening of the site in 1947 and 31 December 1975 was studied up to the end of 1983. The vital state of 96% of the workers was traced satisfactorily and 2277 were found to have died, 572 (25%) from cancer. On average the workers suffered a mortality from all causes that was 2% less than that of the general population of England and Wales and 9% less than that of the population of Cumberland (the area in which the plant is sited). Their mortality from cancers of all kinds was 5% less than that of England and Wales and 3% less than that of Cumberland. In the five years after their first employment Sellafield workers had an overall mortality that was 70% of that of England and Wales, probably due to healthier members of the population being selected for employment. Raised death rates from cancers of several specific sites were found, but only for those of ill defined and secondary sites was the excess statistically significant (30 observed, 19.7 expected). For cancers of the liver and gall bladder there was a significant deficit of deaths (four observed, 10.5 expected). Workers in areas of the plant where radiation exposure was likely were issued with dosimeters to measure their external exposure to ionising radiations. Personal dose records were maintained for workers who entered such areas other than infrequently. Workers with personal dose records ("radiation" workers) had lower death rates from all causes combined than other workers but the death rates from cancer in the two groups were similar. Compared with the general population radiation workers had statistically significant deficits of liver and gall bladder cancer, lung cancer, and Hodgkin''s disease. There were excesses of deaths from myeloma (seven observed, 4.2 expected) and prostatic cancer (19 observed, 15.8 expected) but these were not significant and there was no evidence of an excess of leukaemia (10 deaths observed, 12.2 expected) or cancer of the pancreas (15 observed, 17.8 expected). Non-radiation workers had a significant deficit of leukaemia (one death observed, 5.1 expected) and a significant excess of cancers of ill defined and secondary sites (13 deaths observed, 5.8 expected). For no type of cancer was the ratio of observed to expected deaths significantly different between radiation and non-radiation workers.(ABSTRACT TRUNCATED AT 400 WORDS)     

Mortality (1950-1999) and cancer incidence (1969-1999) in the cohort of Eldorado uranium workers

This study assessed the relationship between radon decay product (RDP) exposure and mortality and cancer incidence in a cohort of 17,660 Eldorado uranium workers first employed in 1932-1980 and followed up through 1999. The analysis was based on substantially revised identifying information and dosimetry for workers from the Beaverlodge and Port Radium uranium mines and for the first time includes workers from a radium and uranium refinery and processing facility in Port Hope, Canada. Overall, male workers had lower mortality rates of all causes and all cancers and lower incidence rates of all cancers compared with the general Canadian male population, a likely healthy worker effect. Individual cancer rates were also reduced except for lung cancer mortality (SMR = 1.31, P < 0.001) and incidence (SIR = 1.23, P < 0.001). The excess relative risk per 100 WLM (ERR/100 WLM) of lung cancer mortality (N = 618, ERR/100 WLM = 0.55, 95% CI: 0.37, 0.78, P < 0.01) and incidence (N = 626, ERR/100 WLM = 0.55, 95% CI: 0.37, 0.81, P < 0.001) increased linearly with increasing RDP exposure. Adjustment for effect modification by time since exposure, exposure rate and age at risk resulted in comparable estimates of risk of lung cancer for all three uranium worksites. RDP exposures and γ-ray doses were not associated with any other cancer site or other cause of death. The risk estimates are in agreement with the results of the pooled analysis of 11 miner cohorts and more recent studies of uranium workers. The current analysis provides more precise risk estimates and compares the findings from the mortality study with the incidence study. Future follow-up of the cohort and joint analysis with other uranium miners' studies should shed more light on the effects of low RDP exposures as experienced by current workers as well as help to understand and address the health risks associated with residential radon.     

An evaluation of several methods for assessing the effects of occupational exposure to radiation

Several methods for the analysis of occupational radiation exposure data, including procedures based on Cox's proportional hazards model, are presented and evaluated. Issues of interest include the contribution of an external control, the effective handling of highly skewed exposure data, and the potential for detecting effects in populations occupationally exposed to radiation. Expressions for evaluating the power of various procedures are derived and applied to data from the Hanford population in order to determine power curves for detecting leukemia effects, with both additive and multiplicative linear models being used. It is found that the introduction of an external control can increase power, although not when an overall adjustment factor must be estimated from the data or when death rates for the study population are substantially lower than those for the control population. It is also found that very little power is lost if exposures are grouped. Finally, the power calculations indicate, as expected, that in analyses of occupationally exposed populations, such as the Hanford workers, there is very little chance of detecting radiation effects at the levels of our current estimates. However, power is reasonably good for detecting effects that are 10 to 15 times larger.     

Historical review of occupational exposures and cancer risks in medical radiation workers

Epidemiological studies of medical radiation workers have found excess risks of leukemia, skin and female breast cancer in those employed before 1950 but little consistent evidence of cancer risk increases subsequently. Occupational radiation-related dose-response data and recent and lifetime cancer risk data are limited for radiologists and radiologic technologists and lacking for physicians and technologists performing fluoroscopically guided procedures. Survey data demonstrate that occupational doses to radiologists and radiologic technologists have declined over time. Eighty mostly small studies of cardiologists and fewer studies of other physicians reveal that effective doses to physicians per interventional procedure vary by more than an order of magnitude. For medical radiation workers, there is an urgent need to expand the limited information on average annual, time-trend and organ doses from occupational radiation exposures and to assess lifetime cancer risks of these workers. For physicians and technologists performing interventional procedures, more information about occupational doses should be collected and long-term follow-up studies of cancer and other serious disease risks should be initiated. Such studies will help optimize standardized protocols for radiologic procedures, determine whether current radiation protection measures for medical radiation workers are adequate, provide guidance on cancer screening needs, and yield valuable insights on cancer risks associated with chronic radiation exposure.     

Solid cancer mortality associated with chronic external radiation exposure at the French atomic energy commission and nuclear fuel company

Studies of nuclear workers make it possible to directly quantify the risks associated with ionizing radiation exposure at low doses and low dose rates. Studies of the CEA (Commissariat à l'Energie Atomique) and AREVA Nuclear Cycle (AREVA NC) cohort, currently the most informative such group in France, describe the long-term risk to nuclear workers associated with external exposure. Our aim is to assess the risk of mortality from solid cancers among CEA and AREVA NC nuclear workers and its association with external radiation exposure. Standardized mortality ratios (SMRs) were calculated and internal Poisson regressions were conducted, controlling for the main confounding factors [sex, attained age, calendar period, company and socioeconomic status (SES)]. During the period 1968-2004, there were 2,035 solid cancers among the 36,769 CEA-AREVA NC workers. Cumulative external radiation exposure was assessed for the period 1950-2004, and the mean cumulative dose was 12.1 mSv. Mortality rates for all causes and all solid cancers were both significantly lower in this cohort than in the general population. A significant excess of deaths from pleural cancer, not associated with cumulative external dose, was observed, probably due to past asbestos exposure. We observed a significant excess of melanoma, also unassociated with dose. Although cumulative external dose was not associated with mortality from all solid cancers, the central estimated excess relative risk (ERR) per Sv of 0.46 for solid cancer mortality was higher than the 0.26 calculated for male Hiroshima and Nagasaki A-bomb survivors 50 years or older and exposed at the age of 30 years or older. The modification of our results after stratification for SES demonstrates the importance of this characteristic in occupational studies, because it makes it possible to take class-based lifestyle differences into account, at least partly. These results show the great potential of a further joint international study of nuclear workers, which should improve knowledge about the risks associated with chronic low doses and provide useful risk estimates for radiation protection.     

Does sunlight have a beneficial influence on certain cancers?

Apperly [1941. The relation of solar radiation to cancer mortality in North America. Cancer Research 1, 191-195] first proposed that increased mortality from cancer in the north than in the south of the USA might be due to the south to north decrease in ambient solar radiation. This inverse association between ambient solar radiation and cancer mortality has been subsequently reported for cancers of the colon, breast, ovary and prostate. While the evidence that sunlight might be related to lower incidence or more favourable outcomes from cancer came initially from ecological studies, case-control and cohort studies have now shown a similar association of sun exposure with risks of colon, breast and prostate cancers in individuals, and other studies in individuals have found that serum and dietary vitamin D levels are associated with reduced risks of colorectal cancer and, less certainly, prostate cancer. Studies in individuals have recently also suggested an effect of sun exposure to reduce risk of non-Hodgkin lymphoma and to increase survival after a diagnosis of melanoma. Data on variation in survival from cancer by season of diagnosis suggest that sun exposure may also improve outcome from cancers of the breast, colon and prostate and Hodgkin lymphoma.     

Updated mortality analysis of radiation workers at Rocketdyne (Atomics International), 1948-2008

Updated analyses of mortality data are presented on 46,970 workers employed 1948-1999 at Rocketdyne (Atomics International). Overall, 5,801 workers were involved in radiation activities, including 2,232 who were monitored for intakes of radionuclides, and 41,169 workers were engaged in rocket testing or other non-radiation activities. The worker population is unique in that lifetime occupational doses from all places of employment were sought, updated and incorporated into the analyses. Further, radiation doses from intakes of 14 different radionuclides were calculated for 16 organs or tissues using biokinetic models of the International Commission on Radiation Protection (ICRP). Because only negligible exposures were received by the 247 workers monitored for radiation activities after 1999, the mean dose from external radiation remained essentially the same at 13.5 mSv (maximum 1 Sv) as reported previously, as did the mean lung dose from external and internal radiation combined at 19.0 mSv (maximum 3.6 Sv). An additional 9 years of follow-up, from December 31,1999 through 2008, increased the person-years of observation for the radiation workers by 21.7% to 196,674 (mean 33.9 years) and the number of cancer deaths by 50% to 684. Analyses included external comparisons with the general population and the computation of standardized mortality ratios (SMRs) and internal comparisons using proportional hazards models and the computation of relative risks (RRs). A low SMR for all causes of death (SMR 0.82; 95% CI 0.78-0.85) continued to indicate that the Rocketdyne radiation workers were healthier than the general population and were less likely to die. The SMRs for all cancers taken together (SMR 0.88; 95% CI 0.81-0.95), lung cancer (SMR 0.87; 95% CI 0.76-1.00) and leukemia other than chronic lymphocytic leukemia (CLL) (SMR 1.04; 95% 0.67-1.53) were not significantly elevated. Cox regression analyses revealed no significant dose-response trends for any cancer. For all cancers excluding leukemia, the RR at 100 mSv was estimated as 0.98 (95% CI 0.82-1.17), and for all leukemia other than CLL it was 1.06 (95% CI 0.50-2.23). Uranium was the primary radionuclide contributing to internal exposures, but no significant increases in lung and kidney disease were seen. The extended follow-up reinforces the findings in the previous study in failing to observe a detectable increase in cancer deaths associated with radiation, but strong conclusions still cannot be drawn because of small numbers and relatively low career doses. Larger combined studies of early workers in the United States using similar methodologies are warranted to refine and clarify radiation risks after protracted exposures.     

Risk of lung cancer and leukemia from exposure to ionizing radiation and potential confounders among workers at the Portsmouth Naval Shipyard

Significantly elevated lung cancer deaths and statistically significantly positive linear trends between leukemia mortality and radiation exposure were reported in a previous analysis of Portsmouth Naval Shipyard workers. The purpose of this study was to conduct a modeling-based analysis that incorporates previously unanalyzed confounders in exploring the exposure-response relationship between cumulative external ionizing radiation exposure and mortality from these cancers among radiation-monitored workers in this cohort. The main analyses were carried out with Poisson regression fitted with maximum likelihood in linear excess relative risk models. Sensitivity analyses varying model components and using other regression models were conducted. The positive association between lung cancer risk and ionizing radiation observed previously was no longer present after adjusting for socioeconomic status (smoking surrogate) and welding fume and asbestos exposures. Excesses of leukemia were found to be positively, though not significantly, associated with external ionizing radiation, with or without including potential confounders. The estimated excess relative risk was 10.88% (95% CI -0.90%, 38.77%) per 10 mSv of radiation exposure, which was within the ranges of risk estimates in previous epidemiological studies (-4.1 to 19.0%). These results are limited by many factors and are subject to uncertainties of the exposure and confounder estimates.     

Twenty years after the Chernobyl accident: solid cancer incidence in various groups of the Ukrainian population

Several major international studies such as those performed on the A-bomb survivors, have shown a clear linkage between the exposure to ionizing radiation and the occurrence of various cancer types including leukemia. While these studies are mostly characterized by high dose rates, studies on populations exposed after the Chernobyl accident are in most cases characterized by low dose rates which are typical for occupational radiation protection. Here, data on more than 60,000 Ukrainian workers who participated in recovery operation works in Chernobyl in 1986–1987, more than 50,000 evacuees from the city of Prypyat and the 30 km zone, and about 360,000 residents of most contaminated territories are presented, which cover a period of observation from 1980 to 2004. For all cancers combined, statistically significant higher incidence rates than the national rates were found only for the recovery workers (standardized incidence ratio (SIR) 117.2%, 95% confidence interval: 114.1–120.3), while those for the other investigated groups were lower. In all groups under study a significant increase of thyroid cancer incidence rates has been registered. This increase appears to be associated, at least partly, with the fallout of radioiodine, and it was found not only in children, but also in adolescents and adults. For example, the most significant excess was found for male recovery workers corresponding to a factor of 8.0. It is important to keep in mind, however, that the contribution of confounding factors such as an intensified thyroid screening after the Chernobyl accident could not be quantified, in the present study. For female recovery workers there was also an excess of breast cancer over the national rates (SIR 190.6%; 95% confidence interval: 163.6–217.7%). An analysis of the two other groups (evacuees and residents of contaminated territories) gave controversial results: relative to the local standard there was a statistically significant excess, while comparison with the national level did not substantiate this conclusion.     

A follow-up study of women in the synthetic rubber industry: study methods

BACKGROUND: Concerns about the possible toxic effects of workplace exposures in the synthetic rubber industry have centered on 1,3-butadiene (BD), styrene and dimethyldithiocarbamate (DMDTC). Our previous mortality studies of over 17,000 male synthetic rubber workers found an excess of leukemia that may be due to BD or BD plus other chemicals. Experimental studies have shown that BD produces mammary tumors in female mice and rats and ovarian tumors in female mice. AIM: This paper presents the methods of a follow-up study that evaluates the mortality experience of women employed in the North American synthetic rubber industry. METHODS: Women employed for at least 1 day at any of eight North American styrene-butadiene rubber plants were followed up from 1943 to 2002. Identifying and work history information were obtained from personnel records. Estimated quantitative exposure to BD, styrene and DMDTC, developed for our previous study of men, were used in this study. External analyses use the standardized mortality ratios (SMRs) to compare the cohort's cause-specific mortality rates to the rates of the female general population of the states or the province where the plants are located. Internal analyses use the Poisson regression and Cox proportional hazards models to examine specific cancer mortality rates in relation to BD, styrene and DMDTC exposure, by comparing an exposed cohort subgroup with the rate of unexposed cohort members.     

Mortality from solid cancers other than lung,liver, and bone in relation to external dose among plutonium and non-plutonium workers in the Mayak Worker Cohort

Exposure to ionizing radiation has well-documented long-term effects on cancer rates and other health outcomes in humans. While in vitro experimental studies had demonstrated that the nature of some radiation effects depend on both total dose of the radiation and the dose rate (i.e., the pattern of dose distribution over time), the question of whether or not the carcinogenic effect of radiation exposure depends on the dose rate remains unanswered. Another issue of interest concerns whether or not concomitant exposure to external gamma rays and inhaled plutonium aerosols has any effect on the external exposure effects. The analyses of the present paper focus on the risk of solid cancers at sites other than lung, liver, and bone in Mayak workers. Recent findings are reviewed indicating that there is no evidence of plutonium dose response for these cancers in the Mayak worker cohort. Then the evidence for differences in the external dose effects among workers with and without the potential for exposure to alpha particles from inhaled plutonium is examined. It is found that there is no evidence that exposure to plutonium aerosols significantly affects the risk associated with external exposure. While the Mayak external dose risk estimate of an excess relative risk of 0.16 per Gy is somewhat lower than an appropriately normalized risk estimate from the Life Span Study of Japanese atomic bomb survivors, the uncertainties in these estimates preclude concluding that the external dose excess relative risks of this group of solid cancers differ in the two cohorts.     

Ionizing radiation and risk of chronic lymphocytic leukemia in the 15-country study of nuclear industry workers

In contrast to other types of leukemia, chronic lymphocytic leukemia (CLL) has long been regarded as non-radiogenic, i.e. not caused by ionizing radiation. However, the justification for this view has been challenged. We therefore report on the relationship between CLL mortality and external ionizing radiation dose within the 15-country nuclear workers cohort study. The analyses included, in seven countries with CLL deaths, a total of 295,963 workers with more than 4.5 million person-years of follow-up and an average cumulative bone marrow dose of 15 mSv; there were 65 CLL deaths in this cohort. The relative risk (RR) at an occupational dose of 100 mSv compared to 0 mSv was 0.84 (95% CI 0.39, 1.48) under the assumption of a 10-year exposure lag. Analyses of longer lag periods showed little variation in the RR, but they included very small numbers of cases with relatively high doses. In conclusion, the largest nuclear workers cohort study to date finds little evidence for an association between low doses of external ionizing radiation and CLL mortality. This study had little power due to low doses, short follow-up periods, and uncertainties in CLL ascertainment from death certificates; an extended follow-up of the cohorts is merited and would ideally include incident cancer cases.     

Bone cancers in Mayak workers

Bone cancer mortality risks were evaluated in 11,000 workers who started working at the "Mayak" Production Association in 1948-1958 and who were exposed to both internally deposited plutonium and external gamma radiation. Comparisons with Russian and U.S. general population rates indicate excess mortality, especially among females, plutonium plant workers, and workers with external doses exceeding 1 Sv. Comparisons within the Mayak worker cohort, which evaluate the role of plutonium body burden with adjustment for cumulative external dose, indicate excess mortality among workers with burdens estimated to exceed 7.4 kBq (relative risk = 7.9; 95% CI = 1.6-32) and among workers in the plutonium plant who did not have routine plutonium monitoring data based on urine measurements (relative risk = 4.1; 95% CI = 1.2-14). In addition, analyses treating the estimated plutonium body burden as a continuous variable indicate increasing risk with increasing burden (P < 0.001). Because of limitations in current plutonium dosimetry, no attempt was made to quantify bone cancer risks from plutonium in terms of organ dose, and risk from external dose could not be reliably evaluated.     

Mortality and occupational exposure to radiation: first analysis of the National Registry for Radiation Workers.

OBJECTIVE--To study cause specific mortality of radiation workers with particular reference to associations between fatal neoplasms and level of exposure to radiation. DESIGN--Cohort study. SETTING--United Kingdom. SUBJECTS--95,217 radiation workers at major sites of the nuclear industry. MAIN OUTCOME MEASURE--Cause of death. RESULTS--Most standardised mortality ratios were below 100: 83 unlagged, 85 with a 10 year lag for all causes; 84 unlagged, 86 lagged for all cancers; and 80 for all known other causes, indicating a "healthy worker effect." The deficit of lung cancer (75 unlagged, 76 lagged) was significant at the 0.1% level. Standardised mortality ratios were significantly raised (214 unlagged, 303 lagged) for thyroid cancer, but there was no evidence for any trend with external recorded radiation dose. Dose of external radiation and mortality from all cancers were weakly correlated (p = 0.10), and multiple myeloma was more strongly correlated (p = 0.06); for leukaemia, excluding chronic lymphatic, the trend was significant (p = 0.03; all tests one tailed). The central estimates of lifetime risk derived from these data were 10.0% per Sv (90% confidence interval less than 0 to 24%) for all cancers and 0.76% per Sv (0.07 to 2.4%) for leukaemia (excluding chronic lymphatic leukaemia). These are, respectively, 2.5 times and 1.9 times the risk estimates recommended by the International Commission on Radiological Protection, but 90% confidence intervals are large and the commission''s risk factors fall well within the range. The positive trend with dose for all cancers, from which the risk estimate was derived, was not significant. The positive association between leukaemia (except chronic lymphatic leukaemia) was significant and robust in subsidiary analyses. This study showed no association between radiation exposure and prostatic cancer. CONCLUSION--There is evidence for an association between radiation exposure and mortality from cancer, in particular leukaemia (excluding chronic lymphatic leukaemia) and multiple myeloma, although mortality from these diseases in the study population overall was below that in the general population. The central estimates of risk from this study lie above the most recent estimates of the International Commission on Radiological Protection for leukaemia (excluding chronic lymphatic leukaemia) and for all malignancies. However, the commission''s risk estimates are well within the 90% confidence intervals from this study. Analysis of combined cohorts of radiation workers in the United States indicated lower risk estimates than the commission recommends, and when the American data are combined with our analysis the overall risks are close to those estimated by the commission. This first analysis of the National Registry for Radiation Workers does not provide sufficient evidence to justify a revision in risk estimates for radiological protection purposes.     

Regional Inequalities in Lung Cancer Mortality in Belgium at the Beginning of the 21st Century: The Contribution of Individual and Area-Level Socioeconomic Status and Industrial Exposure

Being a highly industrialized country with one of the highest male lung cancer mortality rates in Europe, Belgium is an interesting study area for lung cancer research. This study investigates geographical patterns in lung cancer mortality in Belgium. More specifically it probes into the contribution of individual as well as area-level characteristics to (sub-district patterns in) lung cancer mortality. Data from the 2001 census linked to register data from 2001–2011 are used, selecting all Belgian inhabitants aged 65+ at time of the census. Individual characteristics include education, housing status and home ownership. Urbanicity, unemployment rate, the percentage employed in mining and the percentage employed in other high-risk industries are included as sub-district characteristics. Regional variation in lung cancer mortality at sub-district level is estimated using directly age-standardized mortality rates. The association between lung cancer mortality and individual and area characteristics, and their impact on the variation of sub-district level is estimated using multilevel Poisson models. Significant sub-district variations in lung cancer mortality are observed. Individual characteristics explain a small share of this variation, while a large share is explained by sub-district characteristics. Individuals with a low socioeconomic status experience a higher lung cancer mortality risk. Among women, an association with lung cancer mortality is found for the sub-district characteristics urbanicity and unemployment rate, while for men lung cancer mortality was associated with the percentage employed in mining. Not just individual characteristics, but also area characteristics are thus important determinants of (regional differences in) lung cancer mortality.     

Second analysis of mortality of nuclear industry workers in Japan, 1986-1997

IA cohort study of nuclear industry workers was initiated in 1990 to determine the possible health effects of low-level radiation. A total of 5,527 deaths were ascertained among 176,000 male workers who had been retrospectively and/or prospectively followed for an average of 7.9 years during the observation period 1986-1997. Statistical analyses were made mainly on the prospective follow-up outcome of 120,000 workers followed for an average of 4.5 years. The standardized mortality ratio (and its 95% confidence interval) was 0.94 (0.90, 0.97) for 2,934 cases of all causes combined and 0.86 (0.82, 0.91) for 1,305 cases of non-malignant diseases combined, which suggested a healthy worker effect. For 1,191 cases of all cancers combined, it was 0.98 (0.93, 1.04), indicating no difference in mortality from that of the general population. In tests for trend of death rate with increasing radiation dose, no significant correlation was found for all cancers combined. For site-specific cancers, most cancers including leukemia showed no positive correlation with dose, except for cancers of the esophagus, stomach and rectum and multiple myeloma. External causes showed a significant correlation with dose. A separate questionnaire study indicated that these positive findings could be ascribed in part to lifestyle characteristics of the workers. For leukemia only, we attempted to estimate the excess relative risk per unit dose of radiation, which, with reservations because of its wide confidence interval, was within the range of variation of the risks reported in other radiation epidemiological studies. This population must be studied for a longer time and with a consideration of the possible effects of confounding factors.     

The relative biological effectiveness of alpha-radiation during human lung exposure to irradiation

The assessment of the relative biological effectiveness (RBE) for alpha-radiation was held in the cases of inhalation of radon progeny and incorporation of plutonium in lungs. It is based on simulation of lung cancer radiation risk for different types of radiation. Specific radiation risk models developed according to the results of direct epidemiological studies are used for the simulation. These include two published risk models for uranium miners and nuclear workers of the Mayak facilities in the former Soviet Union. Additionally two lung cancer risk models are developed and described for the following cases: population indoor radon exposure and low-linear-energy-transfer reference radiation exposure. By the results of lifetime lung cancer risk simulation the RBE values range from 11 to 12 and from 1.7 to 4.9 for the cases of plutonium incorporation and of radon progeny exposure accordingly. The significant uncertainty of radiation risk models results in significant variation of RBE assessments. Rough estimations of RBE values 90% confidence interval are from unit fraction to 25 and from 2 to 50 for the cases of radon progeny exposure and plutonium incorporation accordingly.