Diagnostic x-rays that expose the thyroid to higher radiation doses than dental x-rays are not associated with a greater risk of thyroid cancer, according to a new study in the American Journal of Epidemiology (March 25, 2013).
These findings underscore the need for a detailed radiation exposure study to better quantify the evaluation of risk, according to the study authors, from the National Cancer Institute's division of cancer epidemiology and genetics.
They analyzed data from the U.S. Radiologic Technologists Study (1983-2006) to estimate thyroid cancer risks related to selected diagnostic procedures. The U.S. Radiologic Technologists Study includes extensive questionnaire data on history of personal diagnostic imaging procedures collected prior to cancer diagnosis.
The researchers assessed potential modifying effects of age and calendar year of the first x-ray procedure in each category of procedures. Incident thyroid cancers (n = 251) were diagnosed among 75,494 technologists.
Their analysis revealed no clear evidence of thyroid cancer risk associated with diagnostic x-rays, except for dental x-rays. They observed a 13% increase in thyroid cancer risk for every 10 reported dental radiographs, "but we found no evidence that the relationship between dental x-rays and thyroid cancer was associated with childhood or adolescent exposures as would have been anticipated," they wrote.
The lack of association of thyroid cancer with x-ray procedures that expose the thyroid to higher radiation doses than do dental x-rays underscores the need to conduct a detailed radiation exposure assessment to enable quantitative evaluation of risk, the study authors concluded.
