Dental x-rays linked to common brain tumor
NEW
YORK: A new study suggests people who had certain kinds of dental
X-rays in the past may be at an increased risk for meningioma, the most
commonly diagnosed brain tumor in the US.
The findings cannot
prove that radiation from the imaging caused the tumors, and the results
are based on people who were likely exposed to higher levels of
radiation during dental X-rays than most are today.
"It's likely
that the exposure association we're seeing here is past exposure, and
past exposure levels were much higher," said Dr. Elizabeth Claus, the
study's lead author and a professor at the Yale School of Medicine in
New Haven, Connecticut.
Claus and her colleagues write in the
journal Cancer that dental X-rays are the most common source of exposure
to ionizing radiation -- which has been linked to meningiomas in the
past -- but most research on the connection is based on people who were
exposed to atomic bombs or received radiation therapy.
There have
been some studies that looked at dental X-rays, but they were from years
ago and included fewer people than the current study, Claus noted.
Still, they were generally in agreement with the new findings.
For
her study, Claus' team recruited 1,433 people diagnosed with
intracranial meningioma -- a tumor that forms in the tissues lining the
brain -- between May 2006 and April 2011. All of the participants were
diagnosed when they were between 20 and 79 years old and they were all
from Connecticut, Massachusetts, North Carolina or the Houston or San
Francisco Bay areas.
For comparison, the researchers also followed
1,350 people who were similar in age, sex and state of residence as the
study group, but who had not been diagnosed with a tumor.
The
study looked at how often people had three different types of dental
X-rays. They included a focused image of one area, a number of images of
the full mouth and a single panoramic view of the entire mouth. These
are known in dentistry parlance as bitewing, full-mouth and panorex
films, respectively.
Each person was interviewed by someone
trained to administer a questionnaire that asked about demographic
details, family history of cancer, pregnancy and medical history. The
interviewers also asked -- among other things -- about the person's
history of dental work and the number of times they had the three types
of dental x-rays taken throughout their life.
The researchers
found that those diagnosed with meningiomas were more than twice as
likely as the comparison group to report ever having had bitewing images
taken.
And regardless of the age when the bitewings were taken,
those who had them yearly or more frequently were at between 40% and 90%
higher risk at all ages to be diagnosed with a brain tumor.
To
put that in perspective, Dr. Paul Pharoah, a cancer researcher at the
University of Cambridge said in a statement the results would mean an
increase in lifetime risk of intracranial meningioma in the U.K. from 15
out of every 10,000 people to 22 in 10,000 people.
Panoramic
X-rays taken at a young age, especially if done yearly or more often
before age 10, also raised the risk of meningiomas by up to five times.
There
was no association between full-mouth X-rays and the tumors, although
the authors note they saw a trend similar to that seen for the bitewing
X-rays.
The lack of association with full-mouth X-rays led one expert to question the connection.
"They
found a small risk (from) a pair of bitewings, but not a full mouth
series, which is multiple bitewings. That inconsistency is impossible to
understand to me," said Dr. Alan Lurie, president of the American
Academy of Oral and Maxillofacial Radiology.
Lurie also echoed
Claus' caution that radiation levels from dental X-rays when some of the
participants were younger was much greater than is used now.
He does warn, however, patients shouldn't assume it's fine for the dentist to take X-rays.
"They should ask why are (dentists) taking this image and what is the benefit to me," he said.
The
American Dental Association put out a statement in response to the
study noting that the interviews relied on participants' memories of how
often they had different types of X-rays years earlier.
The
statement added, "The ADA's long-standing position is that dentists
should order dental X-rays for patients only when necessary for
diagnosis and treatment. Since 1989, the ADA has published
recommendations to help dentists ensure that radiation exposure is as
low as reasonably achievable."
Dr. Sanjay Mallya, an assistant
professor the UCLA School of Dentistry in Los Angeles, said that
patients should be concerned whenever they are exposed to radiation, but
"it's important to emphasize that this concern should not mean that we
shouldn't get X-rays at all."
According to the researchers, "while
dental X-rays are an important tool in well selected patients, efforts
to moderate exposure to (ionizing radiation) to the head is likely to be
of benefit to patients and health care providers alike."