In this study the solid cancer mortality data in the Techa River Cohort in the Southern Urals region of Russia was analyzed. The cohort received protracted exposure in the 1950s due to the releases of radioactive materials from the Mayak plutonium complex. The Extended Techa River Cohort includes 29,849 people who resided along the Techa River between 1950 and 1960 and were followed from January 1, 1950 through December 31, 1999. The analysis was done within the framework of the biologically based two-stage clonal expansion (TSCE) model. It was found that about 2.6% of the 1854 solid cancer deaths (excluding 18 bone cancer cases) could be related to radiation exposure. At age 63, which is the mean age for solid cancer deaths, the excess relative risk (ERR) and excess absolute risk (EAR) were found to be 0.76 Gy(-1) (95% CI 0.23; 1.29) and 33.0 (10(4) PY Gy)(-1) (95% CI 9.8; 52.6), respectively. These risk estimates are consistent with earlier excess relative risk analyses for the same cohort. The change in the ERR with age was investigated in detail, and an increase in risk with attained age was observed. Furthermore, the data were tested for possible signs of genomic instability, and it was found that the data could be described equally well by a model incorporating effects of genomic instability. Results from the TSCE models indicated that radiation received at older ages might have stronger biological effects than exposure at younger ages.
Health effects of in utero exposure to ionizing radiation, especially among adults, are still unclear. The aim of this study was to analyze cancer risk in a cohort of subjects exposed in utero due to releases of nuclear waste into the Techa River in the Southern Urals, taking into account additional postnatal exposure. Analysis for solid cancer was based on 242 cases among 10,482 cohort members, accumulating 381,948 person-years at risk, with follow-up from 1956-2009, while analysis for hematological malignancies was based on 26 cases among 11,070 persons, with 423,502 person-years at risk, with follow-up from 1953-2009. Mean doses accumulated in soft tissues and in red bone marrow during the prenatal period were 4 mGy and 30 mGy, respectively. Additional respective mean postnatal doses received by cohort members were 11 and 84 mGy. Poisson regression analysis was used to estimate the excess relative risk (ERR) of cancer incidence related to in utero and postnatal doses. No association was observed for in utero exposure with solid cancer risk [ERR per 10 mGy: -0.007; 95% confidence interval (CI):
Cancer mortality was studied in 10,552 Swedish hyperthyroid patients treated with 131I between 1950 and 1975. The patients were matched with the Swedish Cause-of-Death Register and the cases of 977 patients who died from cancer or leukemia were studied. The patients had been followed up for an average of 15 years (range 0 to 35 years), and the overall standardized mortality ratio (SMR) was 1.09 [95% confidence interval (CI) = 1.03 to 1.16], with a higher risk for women. The highest mortality was seen during the first year after exposure (SMR = 1.15) and decreased for the following 9 years (SMR = 1.04). The risk of dying from a cancer in the digestive tract and respiratory organs was significantly elevated more than 10 years after exposure, as was the overall cancer mortality (SMR = 1.14). No increased risk was seen for leukemia, bladder cancer or breast cancer. Younger patients and those receiving 131I at higher activity had higher SMRs than older patients and those receiving lower activity. Patients with toxic nodular goiter had higher risk than those with Graves' disease. The lack of increasing mortality over time and with increasing activity of 131I administered argues against a carcinogenic effect of 131I. However, in the case of cancers of the stomach, the 131I exposure could have contributed to the excess mortality from these cancers.
This paper analyzes the data on leukemia and solid cancers of all types among 28,000 people exposed due to discharges of radioactive waste into the Techa River in the South Urals. Cancer mortality rates for the 33-y period since the beginning of the exposure have been estimated. In addition, the paper discusses malignancy cases among the first generation offspring of the exposed people. In comparison with matched control groups, an increased incidence of malignant neoplasms was observed among the exposed population. The leukemia risk, estimated on the basis of the linear model of absolute risk, was 0.85 per 10,000 person-y Gy of the dose accumulated in red bone marrow. Solid cancer risk (except osteosarcoma), estimated using linear model of relative risk, was 0.65 per Gy of dose accumulated in soft tissues. No increase in cancer mortality has been documented for the offspring of the exposed individuals.
Radioactive contamination and population exposure resulted from the operation of the Mayak complex, a plutonium-production facility in the Southern Urals. The highest doses were received by residents along the Techa River into which wastes from the complex leaked between 1949 and 1956. A registry was established containing data on 29,528 persons and information on deaths (9426 by 1982; 6439 death certificates) and cancer cases. Six groups differing in exposure levels were set up for the cohort analysis. The range of doses to red bone marrow in these cohorts was from 1.64 to 0.176 Sv. Leukaemia and solid cancer mortality over the 33-year period of exposure was analysed. The age-standardized total cancer mortality rates and their 95% confidence intervals account for 140 (131-150) and 105 (101-109) per 100,000 person-years for the entire exposed and entire control population. The analysis of cancer mortality in different organs has shown increased rates for leukaemia in one exposed group and for cancers of the uterine corpus and cervix in the other exposed group, as compared to the identical control groups.
At present, direct data on risk from protracted or fractionated radiation exposure at low dose rates have been limited largely to studies of populations exposed to low cumulative doses with resulting low statistical power. We evaluated the cancer risks associated with protracted exposure to external whole-body gamma radiation at high cumulative doses (the average dose is 0.8 Gy and the highest doses exceed 10 Gy) in Russian nuclear workers. Cancer deaths in a cohort of about 21,500 nuclear workers who began working at the Mayak complex between 1948 and 1972 were ascertained from death certificates and autopsy reports with follow-up through December 1997. Excess relative risk models were used to estimate solid cancer and leukemia risks associated with external gamma-radiation dose with adjustment for effects of plutonium exposures. Both solid cancer and leukemia death rates increased significantly with increasing gamma-ray dose (P
The effects of low-dose radiation have been a matter of controversy over the years, and the epidemiologic results have been conflicting. A couple of recent studies have indicated a possible impact on lung cancer mortality from exposure to indoor levels of radon and radon daughters. In this study, selected mortality rates, ie, lung cancer, pancreatic cancer, breast cancer (females only), leukemia, and multiple myeloma were correlated for the counties of Sweden with estimates of average background radiation exposure in these areas. Significant correlations were obtained for lung cancer (males, r = 0.46; females r = 0.55) and pancreatic cancer (males, r = 0.59; females, r = 0.40) , and there was a borderline correlation (r = 0.36; p = 0.04) for leukemia in males. In all, there were positive correlations for eight out of the nine computations made. Since background radiation correlates with urbanization and therefore with smoking, air pollution, etc, the correlations might be spurious due to confounding; on the other hand confounding is a reciprocal phenomenon which suggests that background radiation should to be taken into consideration when widespread risk factors like smoking, coffee drinking, general air pollution, etc, are studied.
Studies of the mortality among nuclear industry workforces have been carried out, and nationally combined analyses performed, in the U.S., the UK and Canada. This paper presents the results of internationally combined analyses of mortality data on 95,673 workers (85.4% men) monitored for external exposure to ionizing radiation and employed for 6 months or longer in the nuclear industry of one of the three countries. These analyses were undertaken to obtain a more precise direct assessment of the carcinogenic effects of protracted low-level exposure to external, predominantly gamma, radiation. The combination of the data from the various studies increases the power to study associations between radiation and specific cancers. The combined analyses covered a total of 2,124,526 person-years (PY) at risk and 15,825 deaths, 3,976 of which were due to cancer. There was no evidence of an association between radiation dose and mortality from all causes or from all cancers. Mortality from leukemia, excluding chronic lymphocytic leukemia (CLL)--the cause of death most strongly and consistently related to radiation dose in studies of atomic bomb survivors and other populations exposed at high dose rates--was significantly associated with cumulative external radiation dose (one-sided P value = 0.046; 119 deaths). Among the 31 other specific types of cancer studied, a significant association was observed only for multiple myeloma (one-sided P value = 0.037; 44 deaths), and this was attributable primarily to the associations reported previously between this disease and radiation dose in the Hanford (U.S.) and Sellafield (UK) cohorts. The excess relative risk (ERR) estimates for all cancers excluding leukemia, and leukemia excluding CLL, the two main groupings of causes of death for which risk estimates have been derived from studies of atomic bomb survivors, were -0.07 per Sv [90% confidence interval (CI): -0.4, 0.3] and 2.18 per Sv (90% CI: 0.1, 5.7), respectively. These values correspond to a relative risk of 0.99 for all cancers excluding leukemia and 1.22 for leukemia excluding CLL for a cumulative protracted dose of 100 mSv compared to 0 mSv. These estimates, which did not differ significantly across cohorts or between men and women, are the most comprehensive and precise direct estimates of cancer risk associated with low-dose protracted exposures obtained to date. Although they are lower than the linear estimates obtained from studies of atomic bomb survivors, they are compatible with a range of possibilities, from a reduction of risk at low doses, to risks twice those on which current radiation protection recommendations are based.(ABSTRACT TRUNCATED AT 400 WORDS)