Dental x-rays and the risk of thyroid cancer: A case-control study

Abstract

The thyroid gland is highly susceptible to radiation carcinogenesis and exposure to high-dose ionising radiation is the only established cause of thyroid cancer. Dental radiography, a common source of low-dose diagnostic radiation exposure in the general population, is often overlooked as a radiation hazard to the gland and may be associated with the risk of thyroid cancer. An increased risk of thyroid cancer has been reported in dentists, dental assistants, and x-ray workers; and exposure to dental x-rays has been associated with an increased risk of meningiomas and salivary tumours. Methods. To examine whether exposure to dental x-rays was associated with the risk of thyroid cancer, we conducted a population-based case-control interview study among 313 patients with thyroid cancer and a similar number of individually matched (year of birth ± three years, gender, nationality, district of residence) control subjects in Kuwait. Results. Conditional logistic regression analysis, adjusted for other upper-body x-rays, showed that exposure to dental x-rays was significantly associated with an increased risk of thyroid cancer (odds ratio = 2.1, 95% confidence interval: 1.4, 3.1) (p=0.001) with a dose-response pattern (p for trend <0.0001). The association did not vary appreciably by age, gender, nationality, level of education, or parity. Discussion. These findings, based on self-report by cases/controls, provide some support to the hypothesis that exposure to dental x-rays, particularly multiple exposures, may be associated with an increased risk of thyroid cancer; and warrant further study in settings where historical dental x-ray records may be available.

Acknowledgements

We thank the thyroid cancer patients and control subjects who participated in the study. We are grateful to Dr A. Al-Asfour, Ms L. Al-Kandari, Ms M. Al-Khaldi, Ms H. Habib, Mr V. David, and Ms O. Zikrallah at the Kuwait Cancer Control Centre and Mrs A. Suresh at Kuwait University for their help and support. The study was funded by the Kuwait Foundation for the Advancement of Sciences and administered by the Kuwait University Research Administration Department. We declare no conflicts of interest. The sponsor of this study had no role in the study design; in the collection, analyses, or interpretation of the data; or in the writing of the report.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.