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


CONCLUSIONS
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.
Memon
Anjum
A
Division of Primary Care and Public Health, Brighton and Sussex Medical School, Falmer, Sussex, UK. a.memon@bsms.ac.uk
Godward
Sara
S
Williams
Dillwyn
D
Siddique
Iqbal
I
Al-Saleh
Khalid
K
D000293:Adolescent; D000328:Adult; D017668:Age of Onset; D000368:Aged; D002291:Carcinoma, Papillary / Q000453:epidemiology / Q000209:etiology; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D003726:Dental Assistants / Q000706:statistics & numerical data; D003815:Dentists / Q000706:statistics & numerical data; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D007730:Kuwait / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D009381:Neoplasms, Radiation-Induced / Q000453:epidemiology* / Q000209:etiology*; D011829:Radiation Dosage; D011832:Radiation Injuries / Q000150:complications* / Q000209:etiology; D011861:Radiography, Dental / Q000009:adverse effects*; D012042:Registries; D018570:Risk Assessment; D013964:Thyroid Neoplasms / Q000175:diagnosis / Q000453:epidemiology* / Q000209:etiology* / Q000517:prevention & control; D055815:Young Adult