RESUMEN
In 1995 the International Agency for Research on Cancer (IARC) completed a study that involved nuclear workers from facilities in the USA, UK and Canada. The only significant, though weak, dose-related associations found were for leukaemia and multiple myeloma. The results for the Canadian cohort, which comprised workers from the facilities of Atomic Energy of Canada Limited (AECL), were compatible with those for the other national cohorts. In 2005, IARC completed a further study, involving nuclear workers from 15 countries, including Canada. In these results, the dose-related risk for leukaemia was not significant but the prominent finding was a statistically significant excess relative risk per sievert (ERR Sv(-1)) for 'all cancers excluding leukaemia'. Surprisingly, the risk ascribed to the Canadian cohort for all cancers excluding leukaemia, driven by the AECL sub-cohort, was significantly higher than the risk estimate for the 15-country cohort as a whole. We have attempted to identify why the results for the AECL cohort were so discrepant and had such a remarkable influence on the 15-country risk estimate. When considering the issues associated with data on the AECL cohorts and their handling, we noted a striking feature: a major change in outcome of studies that involved Canadian nuclear workers occurred concomitantly with the shift to when data from the National Dose Registry (NDR) of Canada were used directly rather than data from records at AECL. We concluded that an important contributor to the considerable upward shift in apparent risk in the 15-country and other Canadian studies that have been based on the NDR probably relates to pre-1971 data and, in particular, the absence from the NDR of the person-years of workers who had zero doses in the calendar years 1956 to 1970. Our recommendation was for there to be a comprehensive evaluation of the risks from radiation in nuclear industry workers in Canada, organisation by organisation, in which some of the anomalies that we have identified might be addressed.
Asunto(s)
Interpretación Estadística de Datos , Exposición a Riesgos Ambientales/estadística & datos numéricos , Neoplasias Inducidas por Radiación/epidemiología , Neoplasias/epidemiología , Plantas de Energía Nuclear/estadística & datos numéricos , Exposición Profesional/estadística & datos numéricos , Modelos de Riesgos Proporcionales , Adulto , Sesgo , Canadá/epidemiología , Estudios de Cohortes , Femenino , Humanos , Incidencia , Internacionalidad , Masculino , Persona de Mediana Edad , Dosis de Radiación , Medición de Riesgo/métodos , Factores de Riesgo , Sensibilidad y Especificidad , Adulto JovenRESUMEN
Lung cancer incidence is analyzed in a large Canadian National Dose Registry (CNDR) cohort with individual annual dosimetry for low-dose occupational exposure to gamma and tritium radiation using the two-stage clonal expansion model (TSCE) and extensions of the model with up to 10 initiation steps. Models with clonal expansion turned off provide very poor fits and are rejected. Characteristic and distinct temporal patterns of excess relative risk (ERR) are found for dose response affecting early, middle, or late stages of carcinogenesis, that is, initiation with one or more stages, clonal expansion, or malignant conversion. Both fixed lag and lag distributions are used to model time from first malignant cell to incidence. Background rates are adjusted for gender and birth cohort. Lacking individual smoking data, surrogate annual smoking doses based on U.S. annual per capita cigarette consumption appear to account for much of the birth cohort effect, leaving radiation dose response relatively unchanged. The mean cumulative exposure for males receiving nonzero cumulative doses of gamma and tritium radiation was 18.2 mSv. The males have a significant dose response with 33 out of a total of 322 lung cancer cases attributable to radiation. There were 78 incident lung cancer among females, (with mean cumulative exposure of 3.8 mSv among females with nonzero exposure). The dose response for females appears smaller than for males but does not differ significantly from zero or from the male dose response. Findings for males include significant dose-response relationships for promotion and malignant conversion, but not initiation, and a protraction effect (sometimes called an inverse-dose-rate effect, where risk increases with protraction of a given dose). The dose response predicted by our analysis appears consistent with the risk for lung cancer incidence in the Japanese atomic bomb survivors cohort, provided that proper adjustments are made for duration of exposure and differences in background rate parameters.
Asunto(s)
Neoplasias Pulmonares/epidemiología , Neoplasias Pulmonares/etiología , Neoplasias Inducidas por Radiación/epidemiología , Exposición Profesional , Canadá , Estudios de Cohortes , Relación Dosis-Respuesta en la Radiación , Femenino , Humanos , Incidencia , Japón , Masculino , Modelos Teóricos , Guerra Nuclear , Radiación Ionizante , Sistema de Registros/estadística & datos numéricos , Medición de Riesgo , Factores Sexuales , SobrevivientesRESUMEN
OBJECTIVE: To describe doses of ionizing radiation and their possible associations with mortality rates and cancer incidence among Canadian dental workers. METHODS: The National Dose Registry (NDR) of Canada was used to assess occupational dose of ionizing radiation received by dental workers. The NDR cohort includes 42,175 people classified as dental workers. Subjects in the NDR were linked to both the Canadian Mortality Database and the Canadian Cancer Database to ascertain cause of death and cancer incidence, respectively. RESULTS: The cohort consisted of 9,051 male and 33,124 female dental workers. A total of 656 incident cases of cancer and 558 deaths were observed. The standardized mortality ratio associated with all-cause mortality was 0.53 (90% confidence interval [CI] 0.49-0.57). The incidence of cancer among dental workers was lower than that for the Canadian population for all cancers except melanoma of the skin (for melanoma, the standardized incidence ratio was 1.46 [90% CI 1.14-1.85]). Occupational doses of ionizing radiation among dentists and dental workers have decreased markedly since the 1950s. CONCLUSIONS: Dental workers receive very low doses of ionizing radiation, and these doses do not appear to be associated with any increase in cancer incidence; the increased incidence of melanoma is more likely related to other risk factors such as exposure to ultraviolet radiation from sunlight.
Asunto(s)
Personal de Odontología , Neoplasias Inducidas por Radiación/etiología , Exposición Profesional/efectos adversos , Radiografía Dental/efectos adversos , Adulto , Canadá/epidemiología , Causas de Muerte , Estudios de Cohortes , Femenino , Humanos , Incidencia , Masculino , Persona de Mediana Edad , Neoplasias Inducidas por Radiación/epidemiología , Neoplasias Inducidas por Radiación/mortalidad , Dosis de RadiaciónRESUMEN
Studies of radiation-associated risks among workers chronically exposed to low doses of radiation are important, both to estimate risks directly and to assess the adequacy of extrapolations of risk estimates from high-dose studies. This paper presents results based on a cohort of 45,468 nuclear power industry workers from the Canadian National Dose Registry monitored for more than 1 year for chronic low-dose whole-body ionizing radiation exposures sometime between 1957 and 1994 (mean duration of monitoring = 7.4 years, mean cumulative equivalent dose = 13.5 mSv). The excess relative risks for leukemia [excluding chronic lymphocytic leukemia (CLL)] and for all solid cancers were 52.5 [95% confidence interval (CI): 0.205, 291] and 2.80 (95% CI: -0.038, 7.13) per sievert, respectively, both associations having P values close to 0.05. Relative risks by dose categories increased monotonically for leukemia excluding CLL but were less consistent for all solid cancers combined. Although the point estimates are higher than those found in other studies of whole-body irradiation, the difference could well be due to chance. Further follow-up of this cohort or the combination of results from multiple worker studies will produce more stable estimates and thus complement the risk estimates from higher-dose studies.