Rationale/Objective: Excess lung cancer risks associated with exposure to inhaled radon decay products among uranium miners has well been established. Although ingestion is also a potentially important route of exposure, the relationship between ingested radon decay products and gastrointestinal cancer risks are not well examined. The objective of this study is to determine the relationship between exposure to radon decay products and the incidence and mortality of gastrointestinal (esophagus, stomach, and colorectal) cancer among men employed as uranium miners in Ontario. Secondly, to determine whether the duration of exposure (dose rate), years since last exposure and age at first exposure modify these associations.
Methods: A cohort of miners who had ever worked in an Ontario uranium mine between 1954 and 1996 was created using the Mining Master File and the National Dose Registry. Cumulative radon exposures measured in Working Level Months (WLM) were previously estimated for each miner. Cancer diagnoses (1964-2004) and cancer deaths (1954-2004) occurring in Ontario were determined by probabilistic record linkage with the Ontario Cancer Registry. To calculate person-years at risk, non-cancer deaths were also ascertained from the Ontario mortality file for the period between 1954 and 2004. Poisson regression methods for grouped data were used to estimate the relative risks (RR) and 95% Confidence Intervals (CI) by exposure level.
Results/Conclusions: The final cohort consisted of 28,273 Ontario uranium miners. By the end of 2004, 34 miners had been diagnosed with esophageal cancer, 86 with stomach cancer, and 359 with colorectal cancer. There were 40 deaths due to esophageal cancer, 69 from stomach cancer, and 176 from colorectal cancer. When comparing the highest cumulative exposure category (>40 WLM) to the referent group (0 WLM), significant increases in both stomach (RRIncidence= 2.30, 95% CI;1.02-5.17 and RRMortality=2.90, 95% CI;1.11-7.63) and colorectal cancers (RRIncidence =1.56, 95% CI;1.07-2.27 and RRMortality =1.74, 95% CI;1.01-2.99) after adjusting for age at risk and period effects. However, no relationships were observed for esophageal cancer. Suggestive evidence of modifying effects of these associations by duration of employment (dose rate) and years since last exposure for colorectal cancer was also observed.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:OTU.1807/24304 |
| Date | 13 April 2010 |
| Creators | Do, Minh T. |
| Contributors | Marrett, Loraine |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | en_ca |
| Detected Language | English |
| Type | Thesis |
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