Risk of central nervous system tumour incidence in a cohort of workers chronically exposed to ionising radiation.

The aim of the present study was to assess the risk of primary central nervous system (CNS) tumour incidence in a cohort of 22,377 Mayak Production Association workers chronically exposed to ionising radiation. There were 96 primary CNS tumours, including 42 cases of glioma and 44 cases of meningioma, registered during the whole follow-up period (1948-2018). The study demonstrated that the risk of primary CNS tumour incidence was associated with sex, attained age, calendar period, tall body height, age at the beginning of exposure, and facility type. There was no association found between risk of CNS tumour incidence and body mass index, smoking (males) and alcohol consumption status. The study did not find an effect of the total external gamma radiation dose absorbed in the brain on risk of CNS tumour incidence irrespective of whether an adjustment for the total external neutron dose absorbed in the brain was included or not. Excess relative risk per 1 Gy of external gamma brain dose was 0.05 (95% confidence interval (CI) -0.30; 0.70) for all CNS tumours, -0.18 (95% CI -; 0.44) for gliomas, and 0.38 (95% CI -0.32; 2.08) for meningiomas without adjustment for total neutron brain dose. There was no effect modification by sex, attained age, age at hire or facility.

Assessment of uncertainties in threshold doses for tissue reactions following acute external radiation exposure.

The study aimed to estimate threshold doses and their uncertainties for some human health effects after short-term high dose-rate radiation exposure by quantile technique and the effective dose threshold technique based on distribution functions. The relative uncertainty (U) of the threshold dose was estimated using the error propagation technique. The quantile technique provided statistically significant estimates of threshold doses for acute radiation syndrome onset (0.44 ± 0.12 Gy, U = 143%) and lethality (1.84 ± 0.44 Gy, U = 117%) but relative uncertainties were high. The effective threshold dose technique provided statistically significant and more precise threshold dose estimates for acute radiation syndrome onset (0.73 ± 0.02 Gy, U = 18%) and lethality (6.83 ± 0.08 Gy, U = 36%), as well as agranulocytosis (3.51 ± 0.03 Gy, U = 16%) and vomiting onset in the prodromal period (1.54 ± 0.02 Gy, U = 16%). Threshold doses estimated for the change in the peripheral blood neutrophil and leukocyte counts during the first days after short-term high dose-rate radiation exposure were not statistically significant.

Incidence risks for cerebrovascular diseases and types of stroke in a cohort of Mayak PA workers.

Incidence risks for cerebrovascular diseases (CeVD) and some types of stroke in a cohort of 22,377 Russian Mayak nuclear workers chronically exposed to ionising radiation and followed up until the end of 2018 are reported. Among total 9469 cases of CeVD, 2078 cases were strokes that included 262 hemorrhagic strokes (HS) and 1611 ischemic strokes (IS). Data evaluation was performed with categorical and dose-response analyses estimating the relative risk (RR) and excess relative risk (ERR) per unit cumulative liver absorbed dose of external gamma-ray or internal alpha-particle exposure based on a linear model utilizing the AMFIT module of the EPICURE software. CeVD incidence was found to be significantly associated with cumulative radiation dose: ERR/Gy was 0.37 (95% confidence interval (CI) 0.27, 0.47) in males and 0.47 (95% CI 0.31, 0.66) in females for external exposure, and 0.31 (95% CI 0.11, 0.59) in males and 0.32 (95% CI 0.11, 0.61) in females for internal exposure. When the model for the analysis of external radiation effect did not include an adjustment for alpha radiation dose (and vice versa), the radiogenic risk estimate increased notably both for males and for females. In contrast, exclusion from or inclusion in the model of additional adjustments for non-radiation factors did not notably change the risk estimates. ERR/Gy of external gamma dose for CeVD incidence significantly decreased with increasing attained age (males and females) and duration of employment (females). No significant associations of either stroke or its types with cumulative gamma-ray dose of external exposure or alpha-particle dose of internal exposure were found.

Registry for chronic radiation syndrome in a worker cohort of the Russian nuclear enterprise, Mayak Production Association.

A registry for chronic radiation syndrome (CRS), a deterministic effect of chronic exposure to external and/or internal radiation at doses and dose rates exceeding thresholds for tissue reactions, was established within a medical and dosimetry database known as 'Clinics', of the Southern Urals Biophysics Institute at the Federal Medical and Biological Agency of Russia. It includes 2068 CRS cases: 1517 (73.4%) in males and 551 (26.6%) in females. The majority of workers (97.9%) diagnosed with CRS at one of the main facilities of the first Russian nuclear enterprise, Mayak Production Association, were hired in the period 1948-1954. On the date of CRS diagnosis, the mean cumulative red bone marrow (RBM) absorbed doses from external gamma rays were 1.1 ± 0.66 Gy in males and 1.0 ± 0.58 Gy (±standard deviation) in females, with mean annual doses of 0.46 ± 0.33 Gy and 0.38 ± 0.22 Gy, respectively, and maximum annual doses of 0.67 ± 0.46 Gy and 0.55 ± 0.34 Gy, respectively. The frequency of CRS cases significantly increased with the increasing cumulative and mean annual RBM absorbed doses from external gamma rays. The paper presents the structure and descriptive characteristics of the CRS registry as well as prospects for its use.

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

OBJECTIVE: Incidence and mortality from ischaemic heart disease (IHD) was studied in an extended cohort of 22,377 workers first employed at the Mayak Production Association during 1948-82 and followed up to the end of 2008. METHODS: Relative risks and excess relative risks per unit dose (ERR/Gy) were calculated based on the maximum likelihood using Epicure software (Hirosoft International Corporation, Seattle, WA). Dose estimates used in analyses were provided by an updated "Mayak Worker Dosimetry System-2008". RESULTS: A significant increasing linear trend in IHD incidence with total dose from external γ-rays was observed after having adjusted for non-radiation factors and dose from internal radiation {ERR/Gy = 0.10 [95% confidence interval (CI): 0.04 to 0.17]}. The pure quadratic model provided a better fit of the data than did the linear one. No significant association of IHD mortality with total dose from external γ-rays after having adjusted for non-radiation factors and dose from internal alpha radiation was observed in the study cohort [ERR/Gy = 0.06 (95% CI: <0 to 0.15)]. A significant increasing linear trend was observed in IHD mortality with total absorbed dose from internal alpha radiation to the liver after having adjusted for non-radiation factors and dose from external γ-rays in both the whole cohort [ERR/Gy = 0.21 (95% CI: 0.01 to 0.58)] and the subcohort of workers exposed at alpha dose <1.00 Gy [ERR/Gy = 1.08 (95% CI: 0.34 to 2.15)]. No association of IHD incidence with total dose from internal alpha radiation to the liver was found in the whole cohort after having adjusted for non-radiation factors and external gamma dose [ERR/Gy = 0.02 (95% CI: not available to 0.10)]. Statistically significant dose effect was revealed in the subcohort of workers exposed to internal alpha radiation at dose to the liver <1.00 Gy [ERR/Gy = 0.44 (95% CI: 0.09 to 0.85)]. CONCLUSION: This study provides strong evidence of IHD incidence and mortality association with external γ-ray exposure and some evidence of IHD incidence and mortality association with internal alpha-radiation exposure. ADVANCES IN KNOWLEDGE: It is the first time the validity of internal radiation dose estimates has been shown to affect the risk of IHD incidence.

Risks of circulatory diseases among Mayak PA workers with radiation doses estimated using the improved Mayak Worker Dosimetry System 2008.

The new Mayak Worker Dosimetry System 2008 (MWDS-2008) was published in 2013 and supersedes the Doses-2005 dosimetry system for Mayak Production Association (PA) workers. It provides revised external and internal dose estimates based on the updated occupational history data. Using MWDS-2008, a cohort of 18,856 workers first employed at one of the main Mayak PA plants during 1948-1972 and followed up to 2005 was identified. Incidence and mortality risks from ischemic heart disease (IHD) (International Classification of Diseases (ICD)-9 codes 410-414) and from cerebrovascular diseases (CVD) (ICD-9 codes 430-438) were examined in this cohort and compared with previously published risk estimates in the same cohort based on the Doses-2005 dosimetry system. Significant associations were observed between doses from external gamma-rays and IHD and CVD incidence and also between internal doses from alpha-radiation and IHD mortality and CVD incidence. The estimates of excess relative risk (ERR)/Gy were consistent with those estimates from the previous studies based on Doses-2005 system apart from the relationship between CVD incidence and internal liver dose where the ERR/Gy based on MWDS-2008 was just over three times higher than the corresponding estimate based on Doses-2005 system. Adjustment for smoking status did not show any effect on the estimates of risk from internal alpha-particle exposure.

Ischemic heart disease in nuclear workers first employed at the Mayak PA in 1948-1972.

Following an earlier study of incidence and mortality of ischemic heart disease (IHD) published in 2010, a second analysis has been conducted based on an extended cohort and five additional years of follow-up. The cohort includes 18,763 workers, of whom 25% were females, first employed at the Mayak PA in 1948-1972 and followed up to the end of 2005. Some of these workers were exposed to external gamma rays only, and others were exposed to a mixture of external gamma-rays and internal alpha-particle radiation. A total of 6,134 cases and 2,629 deaths from IHD were identified in the study cohort. A statistically significant increasing trend was found with total external gamma-ray dose in IHD incidence (ERR/Gy 0.099; 95% CI: 0.045-0.153) after adjusting for non-radiation factors. This value reduced slightly when adjusting for internal liver dose. There was no statistically significant increase trend for internal liver dose in IHD incidence. These findings were consistent with an earlier study. New findings in IHD incidence revealed a statistically significant decrease in IHD incidence among workers exposed to external gamma-rays doses of 0.2-0.5 Gy in relation to the external doses below 0.2 Gy. This decreased risk is heavily influenced by female workers. This finding has never been reported in other studies, and the results should be treated with caution. The findings for IHD mortality are similar to those results in the earlier analysis; there was no statistically significant trend with external gamma-ray dose or for internal liver dose after adjustment for external dose. The risk estimates obtained from these analyses of IHD incidence and mortality in relation to external gamma-rays in the cohort of Mayak workers are generally compatible with those from other large occupational radiation worker studies and the Japanese atomic bomb survivors.

Cerebrovascular diseases in nuclear workers first employed at the Mayak PA in 1948-1972.

Incidence and mortality from cerebrovascular diseases (CVD) (430-438 ICD-9 codes) have been studied in a cohort of 18,763 workers first employed at the Mayak Production Association (Mayak PA) in 1948-1972 and followed up to the end of 2005. Some of the workers were exposed to external gamma-rays only while others were exposed to a mixture of external gamma-rays and internal alpha-particle radiation due to incorporated (239)Pu. After adjusting for non-radiation factors, there were significantly increasing trends in CVD incidence with total absorbed dose from external gamma-rays and total absorbed dose to liver from internal alpha radiation. The CVD incidence was statistically significantly higher among workers with total absorbed external gamma-ray doses greater than 0.20 Gy compared to those exposed to lower doses; the data were consistent with a linear trend in risk with external dose. The CVD incidence was statistically significantly higher among workers with total absorbed internal alpha-radiation doses to liver from incorporated (239)Pu greater than 0.025 Gy compared to those exposed to lower doses. There was no statistically significant trend in CVD mortality risk with either external gamma-ray dose or internal alpha-radiation dose to liver. The risk estimates obtained are generally compatible with those from other large occupational studies, although the incidence data point to higher risk estimates compared to those from the Japanese A-bomb survivors. Further studies of the unique cohort of Mayak workers chronically exposed to external and internal radiation will allow improving the reliability and validating the radiation safety standards for occupational and public exposure.