Lung cancer in Mayak workers

Lung Cancer in the Mayak Workers Cohort: Risk Estimation and Uncertainty Analysis

The workers at the Mayak nuclear facility near Ozyorsk, Russia are a primary source of information about exposure to radiation at low-dose rates, since they were subject to protracted exposures to external gamma rays and to internal exposures from plutonium inhalation. Here we re-examine lung cancer mortality rates and assess the effects of external gamma and internal plutonium exposures using recently developed Monte Carlo dosimetry systems. Using individual lagged mean annual lung doses computed from the dose realizations, we fit excess relative risk (ERR) models to the lung cancer mortality data for the Mayak Workers Cohort using risk-modeling software. We then used the corrected-information matrix (CIM) approach to widen the confidence intervals of ERR by taking into account the uncertainty in doses represented by multiple realizations from the Monte Carlo dosimetry systems. Findings of this work revealed that there were 930 lung cancer deaths during follow-up. Plutonium lung doses (but not gamma doses) were generally higher in the new dosimetry systems than those used in the previous analysis. This led to a reduction in the risk per unit dose compared to prior estimates. The estimated ERR/Gy for external gamma-ray exposure was 0.19 (95% CI: 0.07 to 0.31) for both sexes combined, while the ERR/Gy for internal exposures based on mean plutonium doses were 3.5 (95% CI: 2.3 to 4.6) and 8.9 (95% CI: 3.4 to 14) for males and females at attained age 60. Accounting for uncertainty in dose had little effect on the confidence intervals for the ERR associated with gamma-ray exposure, but had a marked impact on confidence intervals, particularly the upper bounds, for the effect of plutonium exposure [adjusted 95% CIs: 1.5 to 8.9 for males and 2.7 to 28 for females]. In conclusion, lung cancer rates increased significantly with both external gamma-ray and internal plutonium exposures. Accounting for the effects of dose uncertainty markedly increased the width of the confidence intervals for the plutonium dose response but had little impact on the external gamma dose effect estimate. Adjusting risk estimate confidence intervals using CIM provides a solution to the important problem of dose uncertainty. This work demonstrates, for the first time, that it is possible and practical to use our recently developed CIM method to make such adjustments in a large cohort study.

Plutonium production and particles incorporation into the human body

Plutonium is one of the most toxic radioactive substances known. The isotope ²³⁹Pu gained attention when it had become known as a potential explosive material for atomic bombs. This paper describes the main problems encountered during the early years of operation of the first plutonium production plant in the former Soviet Union, the Mayak Production Association (Mayak PA). Mayak PA caused severe radioactive contamination of the environment and exposure personnel and population living in the vicinity areas to high radiation doses. The authors focus on key findings of large-scale studies on the internal dosimetry of workers for use in assessment of radiological risks from exposure to plutonium. This work presents an overview of the important issues for inhalation dose assessments such as generation of plutonium particles, plutonium intake, dissolution of plutonium particles, distribution of plutonium in humans, related exposures and health effects. Understanding the relationship between health effects, radiation dose and route of exposure helps quantify the health risks associated with occupational exposure in the nuclear industry and validate the radiation protection standards used in the Russian Federation and worldwide.

Sex Difference of Radiation Response in Occupational and Accidental Exposure

Ionizing radiation is a well-established cause of deleterious effects on human health. Understanding the risks of radiation exposure is important for the development of protective measures and guidelines. Demographic factors such as age, sex, genetic susceptibility, comorbidities, and various other lifestyle factors influence the radiosensitivity of different subpopulations. Amongst these factors, the influence of sex differences on radiation sensitivity has been given very less attention. In fact, the International Commission on Radiological Protection (ICRP) has based its recommendations on a population average, rather than the data on the radiosensitivity of distinct subpopulations. In this study, we reviewed major human studies on the health risks of radiation exposure and showed that sex-related factors may potentially influence the long-term response to radiation exposure. Available data suggest that long-term radiosensitivity in women is higher than that in men who receive a comparable dose of radiation. The report on the biological effects of ionizing radiation (BEIR VII) published in 2006 by the National Academy of Sciences, United States emphasized that women may be at significantly greater risk of suffering and dying from radiation-induced cancer than men exposed to the same dose of radiation. We show that radiation effects are sex-specific, and long-term radiosensitivity in females is higher than that in males. We also discuss the radiation effects as a function of age. In the future, more systematic studies are needed to elucidate the sex differences in radiation responses across the life continuum - from preconception through childhood, adulthood, and old age - to ensure that boys and girls and men and women are equally protected across ages.

Sex-specific lung cancer risk among radiation workers in the million-person study and patients TB-Fluoroscopy

BACKGROUND

The study of Japanese atomic bomb survivors, exposed briefly to radiation, finds the risk of radiation-induced lung cancer to be nearly three times greater for women than for men. Because protection standards for astronauts are based on individual lifetime risk projections, this sex-specific difference limits the time women can spend in space. Populations exposed to chronic or fractionated radiation were evaluated to learn whether similar differences exist when exposures occur gradually over years.

METHODS AND MATERIALS

Five occupational cohorts within the Million Person Study of Low-Dose Health Effects (MPS) and a Canadian Fluoroscopy Cohort Study (CFCS) of tuberculosis patients who underwent frequent chest fluoroscopic examinations are evaluated. Included are male and female workers at the Mound nuclear facility, nuclear power plants (NPP), and industrial radiographers (IR). Workers at the Mallinckrodt Chemical Works and military participants at aboveground nuclear weapons tests provide information on the risk among males. Cox proportional hazards and Poisson regression models were used to estimate sex-specific radiation risks for lung cancer and to compare any differences.

RESULTS

Overall, 15,065 lung cancers occurred among the 443,684 subjects studied: 50,111 women and 395,573 men. The mean cumulative dose to the lung was 166.3 mGy (range 6 to 1,055 mGy) with the highest among the TB-fluoroscopy patients (mean 1,055 mGy). Mean lung dose for women in the worker cohorts was generally 4 times lower than for men. Of the 12 estimates of radiation-related risk, only one, for male IRs, showed a significant elevation (ERR 0.09; 95% CI 0.02-0.16, at 100 mGy). In contrast, the dose response for male NPP workers was negative (ERR -0.05; 95% CI -0.10, 0.01, at 100 mGy). Combined, these two cohorts provided little evidence for a radiation effect among males (ERR 0.01; 95% CI -0.04, 0.06, at 100 mGy). There was no significant dose-response among females within any cohort. There was no difference in the sex-specific estimates of lung cancer risk.

CONCLUSIONS

There was little evidence that chronic or fractionated exposures increased the risk of lung cancer. There were no differences in the risks of lung cancer between men and women. However, the sex-specific analyses are limited because of small numbers of women and relatively low doses. A more definitive study is ongoing of medical radiation workers which include 85,000 women and 85,000 men (overall mean dose 82 mGy, max 1,140 mGy). Additional understanding will come from the ongoing follow-up of the CFCS.

Risk of malignant skin neoplasms in a cohort of workers occupationally exposed to ionizing radiation at low dose rates

Recently an increasing trend in skin cancer rates has been observed in various populations including those exposed to different radiation types. Risk and dose-response following prolonged radiation exposure remain unclear. The present study was aimed to assess skin melanoma (SM) and non-melanoma skin cancer (NMSC) incidence risks in a cohort of workers occupationally exposed to ionizing radiation at low dose rates over prolonged periods. The study cohort included workers of a Russian nuclear production facility, Mayak Production Association (PA), who were first employed in 1948-1982 and followed up till the end of 2013 (the total of 22,377 individuals with 25% of females). Using AMFIT module of EPICURE software, relative risk and excess relative risk per unit dose (RR and ERR/Sv) were calculated. 60 SM and 294 NMSC cases were registered in members of the study cohort. SM and NMSC incidence was dependent on sex, attained age, age at first employment at the enterprise, type of facility, education level and was not dependent on calendar period of first employment, calendar period of diagnosis, duration of employment, smoking and alcohol consumption statuses. The risk of NMSC incidence was found to be significantly increased in workers occupationally exposed to ionizing radiation at cumulative doses above 2.0 Sv (RR = 2.52; 95% CI: 1.60, 3.97) compared to a reference dose category (0-0.05 Sv). NMSC incidence was found to be significantly associated with cumulative external gamma-dose with ERR/Sv of 0.49 (95% CI: 0.22, 0.90) without an adjustment for neutron dose and 0.51 (95% CI: 0.22, 0.93) while adjusted for neutron dose. Results of the analysis did not reveal a significant association of SM incidence with cumulative dose from external gamma-rays with ERR/Sv of 0.22 (95% CI: -0.29, 1.46) not including a neutron dose adjustment and of 0.15 (95% CI: -0.41, 1.31) while adjusted for dose from neutron exposure.

A comprehensive approach of the gender bias in occupational cancer epidemiology: A systematic review of lung cancer studies (2003-2014)

BACKGROUND

In occupational epidemiology, a male-centered perspective often predominates. We aimed to describe current research practices in terms of gender consideration at different stages of epidemiological studies.

METHODS

A systematic review of occupational lung cancer publications indexed in PubMed was conducted over the period 2003-2014. Articles were described according to the sex composition of their study sample.

RESULTS

In 243 studies, 7 (3%) were women-only, 101 (41%) were mixed, with a disproportionate men-to-women ratio (P50 = 3.5; P75 = 12.4). A shift was observed from mixed and unspecified source populations to men-only final samples. Our results also suggest implicit generalization of results from men-only studies, a lack of tests of interaction and often unjustified sex-adjustment for mixed studies.

CONCLUSIONS

The lower proportion of women in studies cannot be fully explained by their under-representation in the target populations, since there were large numbers of women among both potentially exposed workers and patients diagnosed with lung cancer.

Cancer risk following alpha-emitter exposure

The International Commission on Radiological Protection (ICRP) mandated a task group (Task Group 64) to review recently published epidemiological studies related to cancer risk and incorporated alpha emitters, and to evaluate whether the results might consolidate or challenge assumptions underlying the current radiation protection system. Three major alpha emitters were considered: radon and its decay products, plutonium, and uranium. Results came mainly from cohorts of workers, while for radon, major studies of the general population contributed to a better understanding of the risk of lung cancer at low and chronic exposure. Selection criteria for the review were: assessment of individual exposure of the target organ, long duration of the health survey, availability of attained age at end of follow-up, and adjustment for major co-factors. Task Group 64 is composed of members from ICRP Committees 1 and 2 (because epidemiological and dosimetric expertise were needed) and external experts. A first report (ICRP Publication 115) considered the risk of lung cancer related to inhalation of radon and its decay products. As the estimated excess risk per unit of exposure was higher by a factor of 2 compared with a previous ICRP estimate in 1993, Task Group 64 suggested a reconsideration of the reference levels for the workplace and for the general population. A second report, using the same standardised methodology (lung cancer baselines, population, life expectancy), will include estimation of the cancer risk of nuclear workers exposed to plutonium, focusing on the risk of lung cancer. A comparison of these risks with those of populations exposed to external gamma radiation alone will be made in the near future. For uranium, the results related to the organ-specific dose were too sparse to draw reliable conclusions, despite a recent publication. More research is needed on this topic.

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.

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.

The Mayak Worker Dosimetry System (MWDS-2013): Estimate of Pu Content in Lungs and Thoracic Lymph Nodes From a Limited Set of Organ Autopsy Samples

A method to estimate plutonium content from a limited number of samples of lungs and pulmonary lymph nodes obtained at autopsies of former Mayak Production Association (MPA) workers is described. Historically from one to five samples of lung lobes and one to three respiratory lymph nodes (bronchopulmonary, tracheobronchial and paratracheal) were collected. The samples were used to estimate organ plutonium contents for cases where incomplete sets of samples were obtained, i.e. one to four lung lobes and one to two lymph nodes. This method was developed and validated using individual measurement data from 259 MPA autopsy cases with complete lung samples (five lobes) and three lymph nodes. A good correlation of plutonium content in measurements of two and four lung samples with the content estimate by five lung samples was obtained. The correlations with the individual lymph nodes were less robust than with the lung. The data are used to develop biokinetic, dosimetry and risk models for humans exposed to plutonium.

Lung Cancer Risk from Plutonium: A Pooled Analysis of the Mayak and Sellafield Worker Cohorts

In this study, lung cancer risk from occupational plutonium exposure was analyzed in a pooled cohort of Mayak and Sellafield workers, two of the most informative cohorts in the world with detailed plutonium urine monitoring programs. The pooled cohort comprised 45,817 workers: 23,443 Sellafield workers first employed during 1947-2002 with follow-up until the end of 2005 and 22,374 Mayak workers first employed during 1948-1982 with follow-up until the end of 2008. In the pooled cohort 1,195 lung cancer deaths were observed (789 Mayak, 406 Sellafield) but only 893 lung cancer incidences (509 Mayak, 384 Sellafield, due to truncated follow-up in the incidence analysis). Analyses were performed using Poisson regression models, and were based on doses derived from individual radiation monitoring data using an updated dose assessment methodology developed in the study. There was clear evidence of a linear association between cumulative internal plutonium lung dose and risk of both lung cancer mortality and incidence in the pooled cohort. The pooled point estimates of the excess relative risk (ERR) from plutonium exposure for both lung cancer mortality and incidence were within the range of 5-8 per Gy for males at age 60. The ERR estimates in relationship to external gamma radiation were also significantly raised and in the range 0.2-0.4 per Gy of cumulative gamma dose to the lung. The point estimates of risk, for both external and plutonium exposure, were comparable between the cohorts, which suggests that the pooling of these data was valid. The results support point estimates of relative biological effectiveness (RBE) in the range of 10-25, which is in broad agreement with the value of 20 currently adopted in radiological protection as the radiation weighting factor for alpha particles, however, the uncertainty on this value (RBE = 21; 95% CI: 9-178) is large. The results provide direct evidence that the plutonium risks in each cohort are of the same order of magnitude but the uncertainty on the Sellafield cohort plutonium risk estimates is large, with observed risks consistent with no plutonium risk, and risks five times larger than those observed in the Mayak cohort.

Risk of Lung Cancer Mortality in Nuclear Workers from Internal Exposure to Alpha Particle-emitting Radionuclides

BACKGROUND

Carcinogenic risks of internal exposures to alpha-emitters (except radon) are poorly understood. Since exposure to alpha particles-particularly through inhalation-occurs in a range of settings, understanding consequent risks is a public health priority. We aimed to quantify dose-response relationships between lung dose from alpha-emitters and lung cancer in nuclear workers.

METHODS

We conducted a case-control study, nested within Belgian, French, and UK cohorts of uranium and plutonium workers. Cases were workers who died from lung cancer; one to three controls were matched to each. Lung doses from alpha-emitters were assessed using bioassay data. We estimated excess odds ratio (OR) of lung cancer per gray (Gy) of lung dose.

RESULTS

The study comprised 553 cases and 1,333 controls. Median positive total alpha lung dose was 2.42 mGy (mean: 8.13 mGy; maximum: 316 mGy); for plutonium the median was 1.27 mGy and for uranium 2.17 mGy. Excess OR/Gy (90% confidence interval)-adjusted for external radiation, socioeconomic status, and smoking-was 11 (2.6, 24) for total alpha dose, 50 (17, 106) for plutonium, and 5.3 (-1.9, 18) for uranium.

CONCLUSIONS

We found strong evidence for associations between low doses from alpha-emitters and lung cancer risk. The excess OR/Gy was greater for plutonium than uranium, though confidence intervals overlap. Risk estimates were similar to those estimated previously in plutonium workers, and in uranium miners exposed to radon and its progeny. Expressed as risk/equivalent dose in sieverts (Sv), our estimates are somewhat larger than but consistent with those for atomic bomb survivors.See video abstract at, http://links.lww.com/EDE/B232.

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.

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.

Radiation effects on mortality from solid cancers other than lung, liver, and bone cancer in the Mayak worker cohort: 1948-2008

Radiation effects on mortality from solid cancers other than lung, liver, and bone cancer in the Mayak worker cohort: 1948-2008. The cohort of Mayak Production Association (PA) workers in Russia offers a unique opportunity to study the effects of prolonged low dose rate external gamma exposures and exposure to plutonium in a working age population. We examined radiation effects on the risk of mortality from solid cancers excluding sites of primary plutonium deposition (lung, liver, and bone surface) among 25,757 workers who were first employed in 1948-1982. During the period 1948-2008, there were 1,825 deaths from cancers other than lung, liver and bone. Using colon dose as a representative external dose, a linear dose response model described the data well. The excess relative risk per Gray for external gamma exposure was 0.16 (95% CI: 0.07 - 0.26) when unadjusted for plutonium exposure and 0.12 (95% CI 0.03 - 0.21) when adjusted for plutonium dose and monitoring status. There was no significant effect modification by sex or attained age. Plutonium exposure was not significantly associated with the group of cancers analyzed after adjusting for monitoring status. Site-specific risks were uncertainly estimated but positive for 13 of the 15 sites evaluated with a statistically significant estimate only for esophageal cancer. Comparison with estimates based on the acute exposures in atomic bomb survivors suggests that the excess relative risk per Gray for prolonged external exposure in Mayak workers may be lower than that for acute exposure but, given the uncertainties, the possibility of equal effects cannot be dismissed.

Macrophages as key elements of Mixed-oxide [U-Pu(O2)] distribution and pulmonary damage after inhalation?

Abstract Purpose: To investigate the consequences of alveolar macrophage (AM) depletion on Mixed OXide fuel (MOX: U, Pu oxide) distribution and clearance, as well as lung damage following MOX inhalation.

MATERIALS AND METHODS

Rats were exposed to MOX by nose only inhalation. AM were depleted with intratracheal administration of liposomal clodronate at 6 weeks. Lung changes, macrophage activation, as well as local and systemic actinide distribution were studied up to 3 months post-inhalation.

RESULTS

Clodronate administration modified excretion/retention patterns of α activity. At 3 months post-inhalation lung retention was higher in clodronate-treated rats compared to Phosphate Buffered Saline (PBS)-treated rats, and AM-associated α activity was also increased. Retention in liver was higher in clodronate-treated rats and fecal and urinary excretions were lower. Three months after inhalation, rats exhibited lung fibrotic lesions and alveolitis, with no marked differences between the two groups. Foamy macrophages of M2 subtype [inducible Nitric Oxide Synthase (iNOS) negative but galectin-3 positive] were frequently observed, in correlation with the accumulation of MOX particles. AM from all MOX-exposed rats showed increased chemokine levels as compared to sham controls.

CONCLUSION

Despite the transient reduced AM numbers in clodronate-treated animals no major differences on lung damage were observed as compared to non-treated rats after MOX inhalation. The higher lung activity retention in rats receiving clodronate seems to be part of a general inflammatory response and needs further investigation.

Carcinogenic and inflammatory effects of plutonium-nitrate retention in an exposed nuclear worker and beagle dogs

PURPOSE

Plutonium-nitrate has a moderately rapid translocation rate from the lung to blood stream. Previous studies have shown an unexpected retention of soluble plutonium in the beagles and human case studied here. The inflammatory responses that may be associated with long-term exposure to ionizing radiation were characterized. These pathways include tissue injury, apoptosis, and gene expression modifications. Other protein modifications related to carcinogenesis and inflammation and the various factors that may play a role in orchestrating complex interactions which influence tissue integrity following irradiation were investigated.

MATERIALS AND METHODS

We have examined numerous lung samples from a plutonium-exposed worker, a human control, and a variety of plutonium-exposed beagle dogs using immunohistochemistry and quantitative Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR).

RESULTS

The exposed human showed interstitial fibrosis in peripheral regions of the lung, but no pulmonary tumors. Beagles with similar doses were diagnosed with tumors in bronchiolo-alveolar, peripheral and sub-pleural alveolar regions of the lung. The terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay showed an elevation of apoptosis in tracheal mucosa, tumor cells, and nuclear debris in the alveoli and lymph nodes of the beagles but not in the human case. In both the beagles and human there were statistically significant modifications in the expression of Fas ligand (FASLG), B-cell lymphoma 2 (BCL2), and Caspase 3 (CASP3).

CONCLUSIONS

The data suggests that FASLG, BCL2, CASP3 and apoptosis play a role in the inflammatory responses following prolonged plutonium exposure. Utilizing these unique tissues revealed which pathways are triggered following the internal deposition and long-term retention of plutonium-nitrate in a human and a large animal model.

Radiation risk of malignant neoplasms in organs of main deposition for plutonium in the cohort of Mayak workers with regard to histological types

This paper presents the results of analyses of the incidence of malignant neoplasms in lung, liver, and bone and associated connective tissues among Mayak nuclear workers exposed to both internally incorporated plutonium and to external gamma radiation. The study cohort included 22,373 individuals employed at the reactors and radiochemical and plutonium production facilities of the Mayak nuclear complex during 1948-1982 and followed up to the end of 2004. All analyses were carried out by Poisson regression, and the doses used were derived using a recently available update of organ doses, Mayak doses-2008. There was clear evidence for the linear association between internal plutonium dose and the risk of lung cancer. For males, there was evidence of a significant internal plutonium dose response for all histological types of lung cancer evaluated (adenocarcinoma, squamous-cell, and other epithelial); the estimated excess relative risk (ERR)/Gy for adenocarcinoma was the largest (ERR/Gy = 32.5; 95% CI: 16.3; 71.9), about 11-fold higher than that for squamous-cell lung cancer (ERR/Gy = 3.1; 95% CI: 0.3; 9.1). The relationship between liver cancer risk and plutonium exposure was best described by a linear-quadratic (LQ) function, but the LQ effect was diminished after restricting internal doses <2 Gy. Hepatocellular cancer was the most frequently observed type of liver cancer associated with internal plutonium exposure, and hemangiosarcomas were exclusively observed only at high internal plutonium doses (>4 Gy). For malignant neoplasms of bone and associated connective tissues, the trend was not statistically significant in relation to internal plutonium dose, but a statistically significantly higher risk (RR=13.7; 95% CI= 3.0; 58.5) was found among unmonitored female plutonium workers who were employed in the most hazardous plutonium production facility commissioned prior to 1950.

Lung cancer risks from plutonium: an updated analysis of data from the Mayak worker cohort

Workers at the Mayak nuclear facility in the Russian Federation offer a unique opportunity to evaluate health risks from exposure to inhaled plutonium. Risks of mortality from lung cancer, the most serious carcinogenic effect of plutonium, were evaluated in 14,621 Mayak workers who were hired in the period from 1948-1982, followed for at least 5 years, and either monitored for plutonium or never worked with plutonium. Over the follow-up period from 1953-2008, there were 486 deaths from lung cancer, 446 of them in men. In analyses that were adjusted for external radiation dose and smoking, the plutonium excess relative risk (ERR) per Gy declined with attained age and was higher for females than for males. The ERR per Gy for males at age 60 was 7.4 (95% CI: 5.0-11) while that for females was 24 (95% CI: 11-56). When analyses were restricted to plutonium doses <0.2 Gy, the ERR per Gy for males at age 60 was similar: 7.0 (95% CI: 2.5-13). Of the 486 lung cancer deaths, 105 (22%) were attributed to plutonium exposure and 29 (6%) to external exposure. Analyses of the 12,708 workers with information on smoking indicated that the relationship of plutonium exposure and smoking was likely sub-multiplicative (P = 0.011) and strongly indicated that it was super-additive (P < 0.001). Although extensive efforts have been made to improve plutonium dose estimates in this cohort, they are nevertheless subject to large uncertainties. Large bioassay measurement errors alone are likely to have resulted in serious underestimation of risks, whereas other sources of uncertainty may have biased results in ways that are difficult to predict.

Occupational and environmental causes of lung cancer

Because tobacco smoking is a potent carcinogen, secondary causes of lung cancer are often diminished in perceived importance. The goal of this review is to describe the occurrence and recent findings of the 27 agents currently listed by the International Agency for Research on Cancer (IARC) as lung carcinogens. The IARC's updated assessments of lung carcinogens provide a long-overdue resource for consensus opinions on the carcinogenic potential of various agents. Supplementary new information, with a focus on analytic epidemiologic studies that has become available since IARC's most recent evaluation, are also discussed.

Quantitative assessment of regulatory proteins in blood as markers of radiation effects in the late period after occupational exposure

The objective of this research was quantitative assessment of serum and membrane regulatory proteins in blood from nuclear workers as markers of radiation-induced alterations in immune homeostasis in the late period after protracted exposure of nuclear workers with different doses. The effector and regulatory lymphocytes were measured using a flow cytofluorometer in workers from the main facilities of the Mayak PA (aged ∼60 y up to 80 y) in the late period after combined exposure to external gamma-rays and internal alpha-radiation from incorporated 239Pu. The control group included non-occupationally exposed members of the Ozyorsk population matched by gender and age to the group of Mayak workers. Thirty serum proteins involved in regulation of immune homeostasis, such as growth factors, multifunctional interleukins, pro- and anti-inflammatory cytokines, and their receptors, were measured using ELISA in blood serum specimens from the Radiobiology Human Tissue Repository. The dosimetry estimates were obtained using Doses-2005. The correlation analysis revealed a statistically significant direct relationship of T-killers and plutonium body burden and a decreasing level of T-helpers with accumulated external dose in exposed individuals. There were differences in expression of membrane markers in young regulatory cells (double null T-lymphocytes, NKT-lymphocytes, regulatory T-cells, and an increase of activated forms of T-lymphocytes), which indicated an active role of regulatory cells in maintaining immune homeostasis in terms of protracted exposure. The assessment of regulatory proteins in blood indicated that growth factors (EGF, TGF-β1, PDGF), multifunctional interleukins (IL-17A, IL-18), and pro-inflammatory cytokines (IL-1β and INF-γ) could be potential markers of radiation-induced alterations in protein status. An imbalance of pro- and antiinflammatory proteins in blood and variations of protein profiles at the lower exposure levels (gamma-ray dose <1 Gy, plutonium body burden <0.74 kBq) in the late period after protracted exposure were less pronounced than at the higher exposure levels, which was probably explained by compensatory-adaptive responses in the late period among senile individuals with polypathology.

Cancer deaths and occupational exposure in a group of plutonium workers

An exploratory epidemiological study was conducted for 319 deceased nuclear workers who had intakes of transuranic radionuclides and histories of employment during the time period from 1943 to 1995. The workers were employed at various facilities throughout the United States, including the Department of Energy defense facilities and uranium mining and milling sites. The majority of individuals were involved in documented radiological incidents during their careers. All had voluntarily agreed to donate their organs or whole body to the United States Transuranium and Uranium Registries. External and internal dose assessments were performed using occupational exposure histories and postmortem concentrations of transuranic radionuclides in critical organs. Statistical data analyses were performed to investigate the potential relationship between radiation exposure and causes of death within this population due to cancers of the lungs, liver, and all sites combined while controlling for the effects of other confounders. No association was found between radiation exposure and death due to cancer (α = 0.05). However, statistically significant associations were found between death due to any type of cancer and smoking (yes or no) (odds ratio = 5.41; 95% CI: 1.42 to 20.67) and rate of cigarette smoking (packs per day) (odds ratio = 2.70; 95% CI: 1.37 to 5.30).

Risks from ionising radiation: an HPA viewpoint paper for Safegrounds

Safegrounds is a forum for developing and disseminating good practice guidance on the management of radioactively contaminated land on nuclear and defence sites in the UK. This review has been provided to Safegrounds as a summary of the basis for current radiation risk estimates and the International Commission on Radiological Protection (ICRP) protection system, in a form that will be accessible to a wide range of stakeholders. Safegrounds has also received viewpoint papers from other members who contend that the ICRP methodology results in substantial underestimates of risk, particularly for internal emitters. There is an extensive literature on the risks of radiation exposure, regularly reviewed by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) and other expert groups. These data provide a sound basis for the system of protection recommended by ICRP. The available epidemiological and experimental evidence supports the application of cancer risk estimates derived for acute, high dose, external exposures to low dose exposures to external and internal sources. In the context of radioactively contaminated land on nuclear and defence sites, the national standards for the cleaning up of land and for waste disposal correspond to very low doses, two orders of magnitude less than average annual doses in the UK from natural background radiation (10-20  µSv compared with 2-3 mSv). Risks at such very low doses can only be estimated on the basis of observations after exposure of population groups at much higher doses. The estimated risks at these very low doses, while uncertain, are as likely to be overestimates as underestimates.

Carcinogenesis from inhaled (239)PuO(2) in beagles: Evidence for radiation homeostasis at low doses?

From the early 1970's to the late 1980's, Pacific Northwest National Laboratory conducted life-span studies in beagle dogs on the biological effects of inhaled plutonium ((238)PuO(2), (239)PuO(2), and Pu[NO(3)](4)) to help predict risks associated with accidental intakes in workers. Years later, the purpose of the present follow-up study was to reassess the dose-response relationship for lung cancer in the PuO(2) dogs compared to controls-with particular focus on the dose-response at relatively low lung doses. A PuO(2) aerosol (2.3 mum activity-median aerodynamic diameter, 1.9 mum geometric standard deviation) was administered to six groups of 20 young (18-mo-old) beagle dogs (10 males and 10 females) by inhalation at six different activity levels, as previously described in Laboratory reports. Control dogs were sham-exposed. In dose level 1, initial pulmonary lung depositions were 130 + or - 48 Bq (3.5 + or - 1.3 nCi), corresponding to 1 Bq g lung tissue (0.029 + or - 0.001 nCi g(-1)). Groups 2 through 6 received initial lung depositions (mean values) of 760, 2,724, 10,345, 37,900, and 200,000 Bq (22, 79, 300, 1,100, and 5,800 nCi) PuO(2), respectively. For each dog, the absorbed dose to lungs was calculated from the initial lung burden and the final lung burden at time of death and lung mass, assuming a single, long-term retention function. Insoluble plutonium oxide exhibited long retention times in the lungs. Increased dose-dependent mortality due to lung cancer (bronchiolar-alveolar carcinoma, adenocarcinoma, and epidermoid carcinoma) and radiation pneumonitis (in the highest exposure group) were observed in dogs exposed to PuO(2). Calculated lung doses ranged from a few cGy (lowest exposure level) to 7,764 cGy in dogs that experienced early deaths from radiation pneumonitis. Data were regrouped by lifetime lung dose and plotted as a function of lung tumor incidence. The lung tumor incidence in controls and zero-dose exposed dogs was 18% (5/28). However, no lung tumors were observed in 16 dogs with the lowest lung doses (8 to 22 cGy, mean 14.4 + or - 7.6 cGy), and only one lung tumor was observed in the next 10 dogs with lung doses ranging from 27 to 48 cGy (mean 37.5 + or - 10.9 cGy). By least-squares analysis, a pure-quadratic function represented the overall dose-response (n = 137, r = 0.96) with no apparent dose-related threshold. Reducing this function to three linear dose-response components, we calculated risk coefficients for each. However, the incidence of lung tumors at zero dose was significantly greater than the incidence at low dose (at the p < or = 0.053 confidence level), suggesting a protective effect (radiation homeostasis) of alpha-particle radiation from PuO(2). If a threshold for lung cancer incidence exists, it will be observed in the range 15 to 40 cGy.

Review and evaluation of updated research on the health effects associated with low-dose ionising radiation

While radiation health risks at low doses have traditionally been estimated from high-dose studies, we have reviewed recent literature and concluded that the mechanisms of action for many biological endpoints may be different at low doses from those observed at high doses; that acute doses <100 mSv may be too small to allow epidemiological detection of excess cancers given the background of naturally occurring cancers; that low-dose radiation research should use holistic approaches such as systems-based methods to develop models that define the shape of the dose-response relationship; and that these results should be combined with the latest epidemiology to produce a comprehensive understanding of radiation effects that addresses both damage, likely with a linear effect, and response, possibly with non-linear consequences. Continued research is needed to understand how radiobiology and epidemiology advances should be used to effectively model radiation worker risks.

Lung, liver and bone cancer mortality after plutonium exposure in beagle dogs and nuclear workers

The Mayak Production Association (MPA) worker registry has shown evidence of plutonium-induced health effects. Workers were potentially exposed to plutonium nitrate [(239)Pu(NO(3))(4)] and plutonium dioxide ((239)PuO(2)). Studies of plutonium-induced health effects in animal models can complement human studies by providing more specific data than is possible in human observational studies. Lung, liver, and bone cancer mortality rate ratios in the MPA worker cohort were compared to those seen in beagle dogs, and models of the excess relative risk of lung, liver, and bone cancer mortality from the MPA worker cohort were applied to data from life-span studies of beagle dogs. The lung cancer mortality rate ratios in beagle dogs are similar to those seen in the MPA worker cohort. At cumulative doses less than 3 Gy, the liver cancer mortality rate ratios in the MPA worker cohort are statistically similar to those in beagle dogs. Bone cancer mortality only occurred in MPA workers with doses over 10 Gy. In dogs given (239)Pu, the adjusted excess relative risk of lung cancer mortality per Gy was 1.32 (95% CI 0.56-3.22). The liver cancer mortality adjusted excess relative risk per Gy was 55.3 (95% CI 23.0-133.1). The adjusted excess relative risk of bone cancer mortality per Gy(2) was 1,482 (95% CI 566.0-5686). Models of lung cancer mortality based on MPA worker data with additional covariates adequately described the beagle dog data, while the liver and bone cancer models were less successful.

Biokinetic and dosimetric modelling in the estimation of radiation risks from internal emitters

The International Commission on Radiological Protection (ICRP) has developed biokinetic and dosimetric models that enable the calculation of organ and tissue doses for a wide range of radionuclides. These are used to calculate equivalent and effective dose coefficients (dose in Sv Bq(-1) intake), considering occupational and environmental exposures. Dose coefficients have also been given for a range of radiopharmaceuticals used in diagnostic medicine. Using equivalent and effective dose, exposures from external sources and from different radionuclides can be summed for comparison with dose limits, constraints and reference levels that relate to risks from whole-body radiation exposure. Risk estimates are derived largely from follow-up studies of the survivors of the atomic bombings at Hiroshima and Nagasaki in 1945. New dose coefficients will be required following the publication in 2007 of new ICRP recommendations. ICRP biokinetic and dosimetric models are subject to continuing review and improvement, although it is arguable that the degree of sophistication of some of the most recent models is greater than required for the calculation of effective dose to a reference person for the purposes of regulatory control. However, the models are also used in the calculation of best estimates of doses and risks to individuals, in epidemiological studies and to determine probability of cancer causation. Models are then adjusted to best fit the characteristics of the individuals and population under consideration. For example, doses resulting from massive discharges of strontium-90 and other radionuclides to the Techa River from the Russian Mayak plutonium plant in the early years of its operation are being estimated using models adapted to take account of measurements on local residents and other population-specific data. Best estimates of doses to haemopoietic bone marrow, in utero and postnatally, are being used in epidemiological studies of radiation-induced leukaemia. Radon-222 is the one internal emitter for which control of exposure is based on direct information on cancer risks, with extensive information available on lung cancer induction by radon progeny in mines and consistent data on risks in homes. The dose per unit (222)Rn exposure can be calculated by comparing lung cancer risk estimates derived for (222)Rn exposure and for external exposure of the Japanese survivors. Remarkably similar values are obtained by this method and by calculations using the ICRP model of the respiratory tract, providing good support for model assumptions. Other informative comparisons with risks from external exposure can be made for Thorotrast-induced liver cancer and leukaemia, and radium-induced bone cancer. The bone-seeking alpha emitters, plutonium-239 and radium isotopes, are poorer leukaemogens than predicted by models. ICRP dose coefficients are published as single values without consideration of uncertainties. However, it is clear that full consideration of uncertainties is appropriate when considering best estimates of doses and risks to individuals or specific population groups. An understanding of the component uncertainties in the calculation of dose coefficients can be seen as an important goal and should help inform judgements on the control of exposures. The routine consideration of uncertainties in dose assessments, if achievable, would be of questionable value when doses are generally maintained at small fractions of limits.

The effects of smoking and lung health on the organ retention of different plutonium compounds in the Mayak PA workers

The purpose of this study was to determine the effects of smoking and lung health on the pulmonary and extrapulmonary retention after inhalation of different chemical forms of plutonium with different solubilities in workers from the Mayak Production Association (Ozersk, Russia). Samples of lung, pulmonary lymph nodes, liver and skeleton were obtained from 800 workers who died between 1962-2000. The chemical form of plutonium aerosols, smoking history and presence of lung disease were determined. In workers with normal lung status, all plutonium chemical classes were about equally distributed between the lung parenchyma and pulmonary lymph nodes. The more insoluble chemical forms of plutonium had a greater retention in pulmonary than systemic tissues regardless of smoking history or lung health status. A history of smoking did, however, result in a significantly greater retention of less soluble chemical forms of plutonium in pulmonary tissues of workers with no lung disease. In workers with lung disease, smoking did not significantly influence the terminal organ retention of the different chemical forms of plutonium. These initial data can be used to modify dosimetry and biokinetics models used for estimating radiation risks from plutonium in humans.

Radiotoxicity of inhaled (239)PuO(2) in dogs

Beagle dogs inhaled graded exposure levels of insoluble plutonium dioxide ((239)PuO(2)) aerosols in one of three monodisperse particle sizes at the Lovelace Respiratory Research Institute (LRRI) to study the life-span health effects of different degrees of alpha-particle dose non-uniformity in the lung. The primary noncarcinogenic effects seen were lymphopenia, atrophy and fibrosis of the thoracic lymph nodes, and radiation pneumonitis and pulmonary fibrosis. Radiation pneumonitis/ pulmonary fibrosis occurred from 105 days to more than 11 years after exposure, with the lowest associated alpha-particle dose being 5.9 Gy. The primary carcinogenic effects also occurred almost exclusively in the lung because of the short range of the alpha-particle emissions. The earliest lung cancer was observed at 1086 days after the inhalation exposure. The most common type seen was papillary adenocarcinoma followed by bronchioloalveolar carcinoma. These lung cancer results indicate that a more uniform distribution of alpha-particle dose within the lung has an equal or possibly greater risk of neoplasia than less uniform distributions of alpha-particle dose. The results are consistent with a linear relationship between dose and response, but these data do not directly address the response expected at low dose levels. No primary tumors were found in the tracheobronchial and mediastinal lymph nodes despite the high alpha-particle radiation doses to these lymph nodes, and no cases of leukemia were observed.

County mortality and cancer incidence in relation to living near two former nuclear materials processing facilities in Pennsylvania--an update

A previous county mortality study of populations living near two nuclear materials processing and fabrication facilities in Westmoreland and Armstrong counties in Pennsylvania (1950-1995) was extended through 2004. Noncancer mortality (1996-2004) and cancer incidence (1990-2004) were also evaluated. Among the Westmoreland and Armstrong populations, 10,547 cancer deaths occurred during the period 1996 through 2004 and the relative risk (RR) based on comparisons with six demographically similar counties in western Pennsylvania was 0.97, that is, almost exactly as expected, and no different from our previously published analyses covering the years 1950-1995. The results based on cancer incidence data were very similar to those based on cancer mortality data. Over the years 1990 though 2004, 39,350 incident cancers were reported among residents of Armstrong and Westmoreland counties and the RR based on the six demographically similar counties was 0.99, that is, almost exactly as expected. The number of deaths from nonmalignant conditions was 36,565 and very close to the number expected (RR 1.01). Overall, no increases in cancer or nonmalignant diseases could be attributed to living in counties with nuclear materials processing and fabrication facilities.

Activation of alveolar macrophages after plutonium oxide inhalation in rats: involvement in the early inflammatory response

Alveolar macrophages play an important role in the distribution, clearance and inflammatory reactions after particle inhalation, which may influence long-term events such as fibrosis and tumorigenesis. The objectives of the present study were to investigate the early inflammatory events after plutonium oxide inhalation in rats and involvement of alveolar macrophages. Lung changes were studied from 3 days to 3 months after inhalation of PuO2 of different isotopic compositions (70% or 97% 239Pu) and initial lung deposits (range 2.1 to 43.4 kBq/rat). Analyses of bronchoalveolar lavages showed early increases in the numbers of granulocytes, lymphocytes and multinucleated macrophages. The activation of macrophages was evaluated ex vivo by measurement of inflammatory mediator levels in culture supernatants. TNF-alpha and chemokine MCP-1, MIP-2 and CINC-1 production was elevated from 7 days after inhalation and remained so up to 3 months. In contrast, IL-1beta, IL-6 and IL-10 production was unchanged. At 6 weeks, pulmonary macrophage numbers and activation state were increased as observed from an immunohistochemistry study of lung sections with anti-ED1. Similarly, histological analyses of lung sections also showed evidence of inflammatory responses. In conclusion, our results indicate early inflammatory changes in the lungs of PuO2-contaminated animals and the involvement of macrophages in this process. A dose-effect relationship was observed between the amount of radionuclide inhaled or retained at the time of analysis and inflammatory mediator production by alveolar macrophages 14 days after exposure. For similar initial lung deposits, the inflammatory manifestation appears higher for 97% 239Pu than for 70% 239Pu.

Lung, liver and bone cancer mortality in Mayak workers

Workers at the Mayak nuclear facility in the Russian Federation offer the only adequate human data for evaluating cancer risks from exposure to plutonium. Risks of mortality from cancers of the lung, liver and bone, the organs receiving the largest doses from plutonium, were evaluated in a cohort of 17,740 workers initially hired 1948-1972 using, for the first time, recently improved individual organ dose estimates. Excess relative risk (ERR) models were used to evaluate risks as functions of internal (plutonium) dose, external (primarily gamma) dose, gender, attained age and smoking. By December 31, 2003, 681 lung cancer deaths, 75 liver cancer deaths and 30 bone cancer deaths had occurred. Of these 786 deaths, 239 (30%) were attributed to plutonium exposure. Significant plutonium dose-response relationships (p < 0.001) were observed for all 3 endpoints, with lung and liver cancer risks reasonably described by linear functions. At attained age 60, the ERRs per Gy for lung cancer were 7.1 for males and 15 for females; the averaged-attained age ERRs for liver cancer were 2.6 and 29 for males and females, respectively; those for bone cancer were 0.76 and 3.4. This study is the first to present and compare dose-response analyses for cancers of all 3 organs. The unique Mayak cohort with its high exposures and well characterized doses has allowed quantification of the plutonium dose-response for lung, liver and bone cancer risks based on direct human data. These results will play an important role in plutonium risk assessment.

Radiation doses and risks from internal emitters

This review updates material prepared for the UK Government Committee Examining Radiation Risks from Internal Emitters (CERRIE) and also refers to the new recommendations of the International Commission on Radiological Protection (ICRP) and other recent developments. Two conclusions from CERRIE were that ICRP should clarify and elaborate its advice on the use of its dose quantities, equivalent and effective dose, and that more attention should be paid to uncertainties in dose and risk estimates and their implications. The new ICRP recommendations provide explanations of the calculation and intended purpose of the protection quantities, but further advice on their use would be helpful. The new recommendations refer to the importance of understanding uncertainties in estimates of dose and risk, although methods for doing this are not suggested. Dose coefficients (Sv per Bq intake) for the inhalation or ingestion of radionuclides are published as reference values without uncertainty. The primary purpose of equivalent and effective dose is to enable the summation of doses from different radionuclides and from external sources for comparison with dose limits, constraints and reference levels that relate to stochastic risks of whole-body radiation exposure. Doses are calculated using defined biokinetic and dosimetric models, including reference anatomical data for the organs and tissues of the human body. Radiation weighting factors are used to adjust for the different effectiveness of different radiation types, per unit absorbed dose (Gy), in causing stochastic effects at low doses and dose rates. Tissue weighting factors are used to take account of the contribution of individual organs and tissues to overall detriment from cancer and hereditary effects, providing a simple set of rounded values chosen on the basis of age- and sex-averaged values of relative detriment. While the definition of absorbed dose has the scientific rigour required of a basic physical quantity, the same is not true of the ICRP protection quantities equivalent and effective dose (i.e. those measured in sieverts). The ICRP quantities are intended for practical application in radiological protection and the choice of radiation and tissue weighting factors used in their calculation involves simplifying assumptions regarded as acceptable for this purpose. Best estimates of doses and risks to individuals and specific population groups may be calculated using ICRP biokinetic and dosimetric approaches, but would require the use of best available information on RBE and age-, sex- and population-specific risk factors. Consideration of uncertainties is important in applications such as the assessment of the probability of cancer causation for an individual and in estimating doses in epidemiological studies. While the ICRP system of protection does not take explicit account of uncertainties, an understanding of the various contributions to uncertainty can be seen to be of value when making judgments on the optimisation of protection.

Lung cancer risk of Mayak workers: modelling of carcinogenesis and bystander effect

Lung cancer mortality in the period of 1948-2002 has been analysed for 6,293 male workers of the Mayak Production Association, for whose information on smoking, annual external doses and annual lung doses due to plutonium exposures was available. Individual likelihoods were maximized for the two-stage clonal expansion (TSCE) model of carcinogenesis and for an empirical risk model. Possible detrimental and protective bystander effects on mutation and malignant transformation rates were taken into account in the TSCE model. Criteria for non-nested models were used to evaluate the quality of fit. Data were found to be incompatible with the model including a detrimental bystander effect. The model with a protective bystander effect did not improve the quality of fit over models without a bystander effect. The preferred TSCE model was sub-multiplicative in the risks due to smoking and internal radiation, and more than additive. Smoking contributed 57% to the lung cancer deaths, the interaction of smoking and radiation 27%, radiation 10%, and others cause 6%. An assessment of the relative biological effectiveness of plutonium was consistent with the ICRP recommended value of 20. At age 60 years, the excess relative risk (ERR) per lung dose was 0.20 (95% CI: 0.13; 0.40) Sv(-1), while the excess absolute risk (EAR) per lung dose was 3.2 (2.0; 6.2) per 10(4) PY Sv. With increasing age attained the ERR decreased and the EAR increased. In contrast to the atomic bomb survivors, a significant elevated lung cancer risk was also found for age attained younger than 55 years. For cumulative lung doses below 5 Sv, the excess risk depended linearly on dose. The excess relative risk was significantly lower in the TSCE model for ages attained younger than 55 than that in the empirical model. This reflects a model uncertainty in the results, which is not expressed by the standard statistical uncertainty bands.

Are cancer risks associated with exposures to ionising radiation from internal emitters greater than those in the Japanese A-bomb survivors?

After ingestion or inhalation of radionuclides, internal organs of the human body will be exposed to ionising radiation. Current risk estimates of radiation-associated cancer from internal emitters are largely based on extrapolation of risk from high-dose externally exposed groups. Concerns have been expressed that extrapolated risk estimates from internal emitters are greatly underestimated, by factors of ten or more, thus implying a severe underestimation of the true risks. Therefore, data on cancer mortality and incidence in a number of groups who received exposure predominantly from internal emitters are examined and excess relative risks per Sv are compared with comparable (age at exposure, time since exposure, gender) matched subsets of the Japanese atomic bomb survivor cohort. Risks are examined separately for low LET and high LET internal emitters. There are eight studies informative for the effects of internal low LET radiation exposure and 12 studies informative for the effects of internal high LET radiation. For 11 of the 20 cancer endpoints (subgroups of particular study cohorts) examined in the low LET internal emitter studies, the best estimate of the excess relative risk is greater than the corresponding estimate in the Japanese atomic bomb survivors and for the other nine it is less. For four of these 20 studies, the relative risk is significantly (2-sided P < 0.05) different from that in the Japanese atomic bomb survivors, in three cases greater than the atomic bomb survivor relative risk and in one case less. Considering only those six low LET studies/endpoints with 100 or more deaths or cases, for four out of six studies/endpoints the internal emitter risk is greater than that in the Japanese atomic bomb survivors. For seven of the 24 cancer endpoints examined in the high LET internal emitter studies the best estimate of the ERR in the internal emitter study is greater than the corresponding estimate in the Japanese atomic bomb survivors and for the other 17 it is less. For six studies, the relative risk is significantly (2-sided P < 0.05) different from that in the Japanese atomic bomb survivors, in one case greater than the atomic bomb survivor relative risk and in five cases less. Considering only those eight high LET studies/endpoints with 100 or more deaths or cases, for five out of eight studies/endpoints the internal emitter risk is greater than that in the Japanese atomic bomb survivors. These results suggest that excess relative risks in the internal emitter studies do not appreciably differ from those in the Japanese atomic bomb survivors. However, there are substantial uncertainties in estimates of risks in the internal emitter studies, particularly in relation to lung cancer associated with radon daughter (alpha particle) exposure, so a measure of caution should be exercised in these conclusions.

Mayak worker dosimetry study: an overview

The Mayak Production Association (MPA) was the first plutonium production plant in the former Soviet Union. Workers at the MPA were exposed to relatively large internal radiation intakes and external radiation exposures, particularly in the early years of plant operations. This paper describes the updated dosimetry database, "Doses-2005." Doses-2005 represents a significant improvement in the determination of absorbed organ dose from external radiation and plutonium intake for the original cohort of 18,831 Mayak workers. The methods of dose reconstruction of absorbed organ doses from external radiation uses: 1) archive records of measured dose and worker exposure history, 2) measured energy and directional response characteristics of historical Mayak film dosimeters, and 3) calculated dose conversion factors for Mayak Study-defined exposure scenarios using Monte Carlo techniques. The methods of dose reconstruction for plutonium intake uses two revised models developed from empirical data derived from bioassay and autopsy cases and/or updates from prevailing or emerging International Commission on Radiological Protection models. Other sources of potential significant exposure to workers such as medical diagnostic x-rays, ambient onsite external radiation, neutron radiation, intake of airborne effluent, and intake of nuclides other than plutonium were evaluated to determine their impact on the dose estimates.

Uncertainties analysis for the plutonium dosimetry model, doses-2005, using Mayak bioassay data

The Doses-2005 model is a combination of the International Commission on Radiological Protection (ICRP) models modified using data from the Mayak Production Association cohort. Surrogate doses from inhaled plutonium can be assigned to approximately 29% of the Mayak workers using their urine bioassay measurements and other history records. The purpose of this study was to quantify and qualify the uncertainties in the estimates for radiation doses calculated with the Doses-2005 model by using Monte Carlo methods and perturbation theory. The average uncertainty in the yearly dose estimates for most organs was approximately 100% regardless of the transportability classification. The relative source of the uncertainties comes from three main sources: 45% from the urine bioassay measurements, 29% from the Doses-2005 model parameters, and 26% from the reference masses for the organs. The most significant reduction in the overall dose uncertainties would result from improved methods in bioassay measurement with additional improvements generated through further model refinement. Additional uncertainties were determined for dose estimates resulting from changes in the transportability classification and the smoking toggle. A comparison was performed to determine the effect of using the model with data from either urine bioassay or autopsy data; no direct correlation could be established. Analysis of the model using autopsy data and incorporation of results from other research efforts that have utilized plutonium ICRP models could improve the Doses-2005 model and reduce the overall uncertainty in the dose estimates.

A Nested Case-Control Study of Lung Cancer Risk and Ionizing Radiation Exposure at the Portsmouth Naval Shipyard

Results have been inconsistent between studies of lung cancer risk and ionizing radiation exposures among workers at the Portsmouth Naval Shipyard (PNS). The purpose of this nested case-control study was to evaluate the relationship between lung cancer risk and external ionizing radiation exposure while adjusting for potential confounders that included gender, radiation monitoring status, smoking habit surrogates (socioeconomic status and birth cohort), welding fumes and asbestos. By incidence density sampling, we age-matched 3,291 controls selected from a cohort of 37,853 civilian workers employed at PNS between 1952 and 1992 with 1,097 lung cancer deaths from among the same cohort. Analyses using conditional logistic regression were conducted in various model forms: log-linear (main), linear excess relative risk (ERR), and categorical. Lung cancer risk was positively associated with occupational dose (OR = 1.02 at 10 mSv; 95% CI 0.99- 1.04) but flattened after the inclusion of work-related medical X-ray doses (OR = 1.00; 95% CI 0.98-1.03) in multivariate analyses. Similar risk estimates were observed in the linear ERR model at 10 mSv of cumulative exposure with a 15-year lag.

The 15-Country Collaborative Study of Cancer Risk among Radiation Workers in the Nuclear Industry: estimates of radiation-related cancer risks

A 15-Country collaborative cohort study was conducted to provide direct estimates of cancer risk following protracted low doses of ionizing radiation. Analyses included 407,391 nuclear industry workers monitored individually for external radiation and 5.2 million person-years of follow-up. A significant association was seen between radiation dose and all-cause mortality [excess relative risk (ERR) 0.42 per Sv, 90% CI 0.07, 0.79; 18,993 deaths]. This was mainly attributable to a dose-related increase in all cancer mortality (ERR/Sv 0.97, 90% CI 0.28, 1.77; 5233 deaths). Among 31 specific types of malignancies studied, a significant association was found for lung cancer (ERR/Sv 1.86, 90% CI 0.49, 3.63; 1457 deaths) and a borderline significant (P = 0.06) association for multiple myeloma (ERR/Sv 6.15, 90% CI <0, 20.6; 83 deaths) and ill-defined and secondary cancers (ERR/Sv 1.96, 90% CI -0.26, 5.90; 328 deaths). Stratification on duration of employment had a large effect on the ERR/Sv, reflecting a strong healthy worker survivor effect in these cohorts. This is the largest analytical epidemiological study of the effects of low-dose protracted exposures to ionizing radiation to date. Further studies will be important to better assess the role of tobacco and other occupational exposures in our risk estimates.

Smoking and hormesis as confounding factors in radiation pulmonary carcinogenesis

Confounding factors in radiation pulmonary carcinogenesis are passive and active cigarette smoke exposures and radiation hormesis. Significantly increased lung cancer risk from ionizing radiation at lung doses < 1 Gy is not observed in never smokers exposed to ionizing radiations. Residential radon is not a cause of lung cancer in never smokers and may protect against lung cancer in smokers. The risk of lung cancer found in many epidemiological studies was less than the expected risk (hormetic effect) for nuclear weapons and power plant workers, shipyard workers, fluoroscopy patients, and inhabitants of high-dose background radiation. The protective effect was noted for low- and mixed high- and low-linear energy transfer (LET) radiations in both genders. Many studies showed a protection factor (PROFAC) > 0.40 (40% avoided) against the occurrence of lung cancer. The ubiquitous nature of the radiation hormesis response in cellular, animal, and epidemio-logical studies negates the healthy worker effect as an explanation for radiation hormesis. Low-dose radiation may stimulate DNA repair/apoptosis and immunity to suppress and eliminate cigarette-smoke-induced transformed cells in the lung, reducing lung cancer occurrence in smokers.

Mortality among Radiation Workers at Rocketdyne (Atomics International), 1948–1999

A retrospective cohort mortality study was conducted of workers engaged in nuclear technology development and employed for at least 6 months at Rocketdyne (Atomics International) facilities in California, 1948-1999. Lifetime occupational doses were derived from company records and linkages with national dosimetry data sets. International Commission on Radiation Protection (ICRP) biokinetic models were used to estimate radiation doses to 16 organs or tissues after the intake of radionuclides. Standardized mortality ratios (SMRs) compared the observed numbers of deaths with those expected in the general population of California. Cox proportional hazards models were used to evaluate dose-response trends over categories of cumulative radiation dose, combining external and internal organ-specific doses. There were 5,801 radiation workers, including 2,232 monitored for radionuclide intakes. The mean dose from external radiation was 13.5 mSv (maximum 1 Sv); the mean lung dose from external and internal radiation combined was 19.0 mSv (maximum 3.6 Sv). Vital status was determined for 97.6% of the workers of whom 25.3% (n = 1,468) had died. The average period of observation was 27.9 years. All cancers taken together (SMR 0.93; 95% CI 0.84-1.02) and all leukemia excluding chronic lymphocytic leukemia (CLL) (SMR 1.21; 95% CI 0.69-1.97) were not significantly elevated. No SMR was significantly increased for any cancer or for any other cause of death. The 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 1.00 (95% CI 0.81-1.24), and for all leukemia excluding CLL it was 1.34 (95% CI 0.73-2.45). The nonsignificant increase in leukemia (excluding CLL) was in accord with expectation from other radiation studies, but a similar nonsignificant increase in CLL (a malignancy not found to be associated with radiation) tempers a causal interpretation. Radiation exposure has not caused a detectable increase in cancer deaths in this population, but results are limited by small numbers and relatively low career doses.

Uncertainty analysis of relative biological effectiveness of alpha-radiation for human lung exposure

Assessment of relative biological effectiveness (RBE) for a radiation in the cases of inhalation of radon progeny and incorporation of plutonium in lung is based on simulation of lung cancer radiation risk for alpha and external reference types of radiation. Specific radiation risk models developed on the results of direct epidemiological studies are used for simulation. These include published risk models for nuclear workers of the Mayak facilities in the former Soviet Union exposed to incorporated plutonium (Kreisheimer et al., 2003; Gilbert et al., 2004) and underground miners exposed to radon progenies (BEIR VI, 1999). Additionally, a lung cancer risk model is developed for a case of population indoor radon exposure. Lung cancer risk related to external exposure is estimated using the risk model developed for the analyses of Japanese atomic bomb survivors (Preston et al., 2003). Uncertainties of risk models parameters are considered and the uncertainties of RBE are estimated using the results of lifetime lung cancer risk simulation, which is done implementing a Monte Carlo approach. Estimated median value of RBE in case of indoor radon exposure is 1.5 with 90% range 0.4-7. In the case of the two models developed by BEIR VI for lung cancer risk due to radon exposure in underground miners, the median values of RBE are 2.1 and 4.4 with 90% ranges 0.3-17 and 0.7-45, respectively. The two different models for lung cancer risk related to plutonium exposure resulted in close estimates of RBE: median value of 12 and 13 with 90% range 4-104 and 4-136, respectively.

A nested case-control study of leukemia mortality and ionizing radiation at the Portsmouth Naval Shipyard

A nested case-control study using conditional logistic regression was conducted to evaluate the exposure-response relationship between external ionizing radiation exposure and leukemia mortality among civilian workers at the Portsmouth Naval Shipyard (PNS), Kittery, Maine. The PNS civilian workers received occupational radiation exposure while performing construction, overhaul, repair and refueling activities on nuclear-powered submarines. The study age-matched 115 leukemia deaths with 460 controls selected from a cohort of 37,853 civilian workers employed at PNS between 1952 and 1992. In addition to radiation doses received in the workplace, a secondary analysis incorporating doses from work-related medical X rays and other occupational radiation exposures was conducted. A significant positive association was found between leukemia mortality and external radiation exposure, adjusting for gender, radiation worker status, and solvent exposure duration (OR = 1.08 at 10 mSv of exposure; 95% CI = 1.01, 1.16). Solvent exposure (including benzene and carbon tetrachloride) was also significantly associated with leukemia mortality adjusting for radiation dose, radiation worker status, and gender. Incorporating doses from work-related medical X rays did not change the estimated leukemia risk per unit of dose.

Protracted radiation exposure and cancer mortality in the Techa River Cohort

In the 1950s many thousands of people living in rural villages on the Techa River received protracted internal and external exposures to ionizing radiation from the release of radioactive material from the Mayak plutonium production complex. The Extended Techa River Cohort includes 29,873 people born before 1950 who lived near the river sometime between 1950 and 1960. Vital status and cause of death are known for most cohort members. Individualized dose estimates have been computed using the Techa River Dosimetry System 2000. The analyses provide strong evidence of long-term carcinogenic effects of protracted low-dose-rate exposures; however, the risk estimates must be interpreted with caution because of uncertainties in the dose estimates. We provide preliminary radiation risk estimates for cancer mortality based on 1,842 solid cancer deaths (excluding bone cancer) and 61 deaths from leukemia. The excess relative risk per gray for solid cancer is 0.92 (95% CI 0.2; 1.7), while those for leukemia, including and excluding chronic lymphocytic leukemia, are 4.2 (CI 95% 1.2; 13) and 6.5 (CI 95% 1.8; 24), respectively. It is estimated that about 2.5% of the solid cancer deaths and 63% of the leukemia deaths are associated with the radiation exposure.