Effects of Low Doses and Low Dose Rates of External Ionizing Radiation: Cancer Mortality among Nuclear Industry Workers in Three Countries

Abstract

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)

The effect of censoring on cancer risk estimates based on the Canadian National Dose Registry of occupational radiation exposure

“…With the establishment of centralized occupational radiation exposure registries similar to the NDR of Canada in a number of countries (Boyle et al, 1997), and the trend toward pooling of such data at the international level (cf. Cardis et al, 1995), it is important that sources of uncertainty in risks estimates derived from exposure data in such registries be understood. In this paper, we have examined an important source of uncertainty, common to all dose registries, due to the detection limits of radiation dosimeters used to monitor worker exposures.…”

“…Exposure measurement error of this type is augmented as periodic radiation exposure measurements are summed to obtain cumulative exposure measurements for individuals in the NDR. Censoring of radiation exposure data also occurs in other studies of this type, including a pooled study of radiation workers in Canada, the United States, and the United Kingdom (Cardis et al, 1995).…”

“…Exposure measurement error of this type is augmented as periodic radiation exposure measurements are summed to obtain cumulative exposure measurements for individuals in the NDR. Censoring of radiation exposure data also occurs in other studies of this type, including a pooled study of radiation workers in Canada, the United States, and the United Kingdom (Cardis et al, 1995).Individual dosimeter measurements are also subject to a number of other sources of error, both random and systematic. In particular, the dosimeter measurement itself is a proxy for the internal exposure of relevant organs to ionizing radiation.…”

Evaluating shielding effectiveness for reducing space radiation cancer risks

“…The risk of heart disease for ions is largely unknown because only one report (considered a pilot study by the authors of the report) has been made on the effects of HZE ions on heart disease (Yang et al, 1982), and human data for low LET radiation at low dose-rates is inconclusive on the level of risk to be expected (Howe et al, 2004;Cardis et al, 1995). CNS risks have the potential to impact both short-term and career radiation limits and mitigation approaches (NRC, 1996).…”

Curvilinearity in the dose-response curve for cancer in Japanese atomic bomb survivors.

“…Cancers in general, and leukemias in particular, are assumed to be stochastic effects for which there generally are no expectations of a dose threshold; however, a threshold might be expected for certain other categories of deterministic effects such as sterility or cataract induction (1). Because significant excess leukemia risk has been observed in various occupationally exposed groups (28) in which total doses generally are administered in a hyperfractionated manner and also among those exposed to small doses (< 20 mSv) of Xirradiation in utero (29), it is highly likely that there is no threshold in the leukemia dose response.…”