Exposure to ionizing radiation is the best-known environmental risk factor for meningioma, the most common type of primary brain tumor in adults. In the United States, dental X-rays are the most common source of ionizing radiation, and new research links regular dental X-rays to meningiomas. According to the study, adult patients diagnosed with meningiomas are nearly twice as likely to have had bitewing X-rays yearly, or even more frequently, than adults who are tumor free.

Earlier studies linking ionizing radiation to a higher risk of meningioma looked at small numbers of people exposed to ionizing radiation from atomic bombs or from treatments for cancer and other diseases. The new study examined records of 1,433 patients who were 20 to 79 years old when they received a diagnosis of meningioma. Their data were compared with data from 1,350 age-matched controls. The mean age of cases and controls was 57 years. People who remembered having annual bitewing X-rays were as much as 1.9 times more likely to be diagnosed with meningioma as adults. Panorex dental X-rays received before 10 years of age raised the meningioma risk even more, by 4.9 times, and increased the overall risk (irrespective of age) by nearly three times.

The researchers point out that dental X-rays taken today use much lower doses of radiation than those received by participants in this study. In fact, absorbed radiation doses from dental X-rays have declined 60% in recent years as a result of faster X-ray film speed, digital sensor technology, X-ray beam collimation, and patient shielding, according to the American Academy of Oral and Maxillofacial Radiology.

"Efforts to moderate exposure to [ionizing radiation] to the head [are] likely to be of benefit to patients and health care providers alike," write the study authors, especially since exposure to ionizing radiation from other medical imaging procedures has increased sixfold since 1980. The American Dental Association, in its latest guidelines, asked dentists to weigh the risks and benefits associated with the use of dental X-rays at preset intervals.-Carol Potera

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