Frequent exposure to dental x-rays correlated with a twofold increase in the risk of meningioma, investigators reported.

Regardless of age at the time of exposure, people who reported at least annual bitewing x-rays had a significantly higher risk of meningioma.

Frequent exposure to panorex films or exposure at a young age also was associated with an increased risk of meningioma, particularly among individuals exposed before age 10, as reported online in Cancer.

“The findings presented here are important, because dental x-rays remain the most common artificial source of exposure to ionizing radiation for individuals living in the U.S.,” Elizabeth B. Claus, MD, PhD, of Yale University, and co-authors wrote in the discussion of their findings.

“The primary environmental (and generally modifiable) risk factor consistently identified for meningioma is exposure to ionizing radiation,” they added. The American Dental Association has issued a statement encouraging dentists to weigh the risks and benefits of dental x-rays and noting a paucity of evidence to use x-rays to search for occult disease (J Am Dent Assoc 2006; 137: 1304-1312), the authors noted. Studies have shown that exposure to ionizing radiation increases the relative risk of meningioma by as much as tenfold. Many of the studies, however, included patients exposed to high levels of radiation, such as survivors of atomic bombs, the authors wrote in their introduction. Studies that have concentrated on exposure to lower levels of ionizing radiation are few and have fewer than 200 total cases. Studies focusing on the risks of dental x-rays have produced suggestive evidence but have involved few cases and have spanned an era when higher-dose x-ray methods were used, the authors continued. No recent studies have examined associations between dental x-rays and meningioma during the era when radiation doses for conventional x-rays have decreased and newer imaging techniques, such as computed tomography, have been introduced. To update the potential associations, Claus and colleagues examined records for 1,433 patients who had meningioma diagnoses from May 2006 through April 2011. They compiled a control group matched for age, sex, and geography. Overall, the patients were twice as likely as the control group to report a history of at least annual exposure to bitewing x-rays (OR 2.0). A significant difference persisted across all age groups: <10, OR 1.4 10 to 19, OR 1.6 20 to 49, OR 1.9 ≥50, OR 1.5 Less-than-annual exposure to bitewing x-rays also was associated with increased odds for meningioma, ranging from 1.1 to 1.6 across age groups. The differences were significant for all but the oldest age group. Annual or more frequent panorex dental x-rays increased the odds for meningioma by 2.7 to 3.0 in the three oldest age groups, and any exposure to panorex imaging before age 10 was associated with a meningioma odds ratio of 4.9. The authors acknowledged the inherent potential for under- and over-reporting in epidemiologic studies (in this case, the frequency of dental x-rays). They also pointed out the unknown potential for genetic variation in susceptibility to ionizing radiation exposure. Finally, the authors acknowledged that some of the exposures occurred before lower-dose dental x-ray techniques were widely used. In response to a request from MedPage Today and ABC News, clinicians and authorities on radiation safety weighed in on the findings. Henry D. Royal, MD, of Washington University in St. Louis, called the study flawed and cited the absence of radiation doses and lack of control for nondental radiation exposures. "Causality seems improbable," Royal responded in an email. "The dose to the brain from dental x-rays should be trivial. To know whether dental x-rays caused meningiomas, you would want to know the radiation dose to the part of the brain where the meningioma occurred, and you would need to show that there was a statistically significant dose response." In contrast, health physics specialist Steven King, of Penn State-Hershey Medical Center in Pennsylvania, credited the authors with confirming an association between dental x-rays and meningioma reported in previous studies. "The current study is well done and confirms that even in the 'modern era,' radiation exposure from repeated dental x-rays conveys an increased risk of these tumors," King wrote in an email. Robert J. Emery, DrPH, of the University of Texas at Houston, said the study points to a need for closer examination of the issues, such as actual review of patient records, documentation of the types of exams and imaging, and radiation dose. He also pointed out that dentists and patients can take precautions to limit radiation exposure.