Aim: The current research aimed to study the association between exposure to low-dose radiation fallout after the Chernobyl accident in 1986 and the incidence of cancer in Sweden. Methods: A nationwide study population, selecting information from nine counties out of 21 in Sweden for the period from 1980 – 2010. In the first study, an ecological design was defined for two closed cohorts from 1980 and 1986. A possible exposure response pattern between the exposure to 137Cs on the ground and the cancer incidence after the Chernobyl nuclear power plant accident was investigated in the nine northernmost counties of Sweden (n=2.2 million). The activity of 137Cs at the county, municipality and parish level in 1986 was retrieved from the Swedish Radiation Safety Authority (SSI) and used as a proxy for received dose of ionizing radiation. Information about diagnoses of cancer (ICD-7 code 140-209) from 1958 – 2009 were received from the Swedish Cancer Registry, National Board of Health and Welfare (368,244 cases were reported for the period 1958 to 2009). The incidence rate ratios were calculated by using Poisson Regression for pre-Chernobyl (1980 – 1986) and post-Chernobyl (1986 – 2009) using average deposition of 137Cs at three geographical levels: county (n=9), municipality (n=95), and parish level (n=612). Also, a time trend analysis with age standardized cancer incidence in the study population and in the general Swedish population was drawn from 1980 – 2009. In the second study, a closed cohort was defined as all individuals living in the three most contaminated counties in mid-Sweden in 1986. Fallout of 137Cs was retrieved as a digital map from the Geological Survey of Sweden, demographic data from Statistics Sweden, and cancer diagnosis from the Swedish Cancer Registry, National Board of Health and Welfare. Individuals were assigned an annual 137Cs exposure based on their place of residence (1986 through 1990), from which 5-year cumulative 137Cs exposures were calculated, accounting for the physical decay of 137Cs and changing residencies. Hazard ratios for having cancer during the follow-up period, adjusted for age, sex, rural/non-rural residence, and pre-Chernobyl total cancer incidence, were calculated. Results: No obvious exposure-response pattern in the age-standardized total cancer incidence rate ratios could be seen in the first study. However, a spurious association between the fallout and cancer incidence was present, where areas with the lowest incidence of cancer before the accident coincidentally had the lowest fallout of cesium-137. Increasing the geographical resolution of exposure from the average values of nine counties to the average values of 612 parishes resulted in two to three times higher degree of variance explanation by regression model. There was a secular trend, with an increase in age standardized incidence of cancer from 1980 – 2009. This trend was stronger in the general Swedish population compared to the nine counties of the present study. In the second study, 734,537 people identified were divided into three exposure categories: the first quartile was low exposure (0.0 to 45.4 kBq/m2), the second and third quartiles were intermediate exposure (45.41 to 118.8 kBq/m2), and the fourth quartile was highest exposure (118.81 to 564.71 kBq/m2). Between 1991 and 2010, 82,495 cancer cases were registered in the three counties. Adjusted HRs (95% CI) were 1.03 (1.01 to 1.05) for intermediate exposure, and 1.05 (1.03 to 1.07) for the highest exposure, when comparing to the reference exposure. Conclusion: Using the ecological data, there was no exposure response trend; however, after refining the data to the individual level of exposure, there was an overall exposure response pattern. Nonetheless, due to the time dependency, these results were restricted to the age group of 25 – 49 among males. Using register-based data only, for determining the association between low-dose exposure to radiation and the risk of developing cancer, is difficult since we cannot control for other significant factors that are associated with cancer.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:uu-380570 |
| Date | January 2019 |
| Creators | Alinaghizadeh, Hassan |
| Publisher | Uppsala universitet, Arbets- och miljömedicin, Uppsala |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Licentiate thesis, comprehensive summary, info:eu-repo/semantics/masterThesis, text |
| Format | application/pdf, application/pdf |
| Rights | info:eu-repo/semantics/openAccess, info:eu-repo/semantics/openAccess |
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