Background: Public health concern about nuclear activities have existed since the 1980s. Most studies on this subject investigated childhood leukemia. Thyroid cancer may be another health outcome of interest, because some nuclear installations are a potential source of radioactive iodine isotopes in the environment and because thyroid cancer is known to occur after exposure to these isotopes.
Methods: This study describes an ecological study investigating whether there is excessive thyroid cancer incidence among residents living in the vicinity of nuclear sites. Single-site analyses using indirect standardization (standardized incidence ratios [SIRs]) and Poisson regression modeling (rate ratios [RRs]) were conducted. The proximity area is typically defined as a circular zone with a radius of 20 km centered on the site. However, the choice of the size of this area is somewhat arbitrary. Therefore, a sensitivity analysis was carried out to investigate whether the results vary with radii of increasing proximity.
Results: No increased thyroid cancer incidence was found within the 20 km proximity area around the nuclear power plants of Doel (SIR=0.74 [95% confidence interval (CI)=0.64; 0.84] and RR=0.72 [95% CI=0.63; 0.83]) and Tihange (SIR=0.86 [95% CI=0.70; 1.01] and RR=0.85 [95% CI=0.70; 1.02]). For the sites of Mol-Dessel and Fleurus, where a combination of nuclear research and industrial activities are located, the incidences of thyroid cancer within the 20 km proximity area were higher than expected (Mol-Dessel: SIR=1.19 [95% CI=1.01; 1.36] and RR=1.19 [95% CI=1.02; 1.38]; Fleurus: SIR=1.15 [95% CI=1.02; 1.28] and RR=1.17 [95% CI=1.04; 1.33]). For Chooz, a French nuclear power plant close to the Belgian border, the results were unstable as a result of the small population denominator. For all Belgian nuclear sites, the results were generally insensitive to the choice of the proximity area.
Conclusions: No evidence for excessive thyroid cancer incidence around the Belgian nuclear power plants was found. On the other hand, an increased incidence of thyroid cancer was observed around the sites with other nuclear activities. Further research is recommended to verify whether the observed increases could be related to the site-specific nuclear activities.