Expert discusses dental x-rays and thyroid cancer risk

Recently, a medical expert at CNN Health reviewed the risk of thyroid cancer associated with repeated exposure to dental x-rays.

Otis Brawley, who is the American Cancer Society's chief medical officer, told a curious reader from Georgia that the apparent nationwide increase in cases of thyroid cancer is almost certainly unrelated to dental x-rays.

Between 1980 and 2007, rates of the disease jumped from 6 female and 2.5 male cases per 100,000 people to 17 female and 5.8 male cases per 100,000 people, Brawley states. This rise in incidence can be unnerving, he said, but is almost completely attributable to increases in the amount and efficiency of medical scans, which can detect small nodules that would previously have gone unnoticed.

However, a small fraction of the general increase in thyroid cancer does appear to be due to the detection of more large tumors, he said.

Dental x-rays do entail a low dose of radiation, measuring between 0.03 and 0.15 millisieverts (mSv), according to the American Dental Association. Brawley noted that while lead aprons are used to shield the torsos of dental patients, similar collars could potentially be used to cover the neck during a dental x-ray.

That said, he added that most radiologists do not see a need for such collars in that situation. Instead, ionizing radiation from medical scans is thought to only become a problem in larger doses, such as those created by repeated CT scanning.

To put things in perspective, the Environmental Protection Agency (EPA) estimates that the average American absorbs 6 mSv of radiation per year from cosmic and terrestrial radiation, the environment and man-made causes, like smoking. A dental x-ray is approximately 1 percent of that yearly dose.

For reference, the EPA states tjhat the human body itself naturally gives off 0.4 mSv annually, the equivalent of more than three dental x-rays.

While at least one study, published in the March 2010 issue of Acta Oncologica, has made a modest connection between dental x-rays and thyroid cancer, its conclusions were largely limited to dental workers, whose exposure to ionizing radiation would be higher than any patient's exposure.