Based on the findings,
reported in
the Dec. 14/28 issue of the Archives
of Internal Medicine, the
study authors, joined by Archives
editor Dr. Rita F. Redberg,
are calling on clinicians to limit radiation exposure
to patients.
"CT has become so quick
that we
are using it so commonly, and we have lowered our threshold for using
it—meaning we use it for patients who really are unlikely to have any
underlying disease," said Dr. Rebecca Smith-Bindman, a professor in
residence in the department of radiology at the University of California, San
Francisco, and lead author of one of the studies. Although it's a
"fabulous diagnostic tool," she said she believes "we have
lowered it to the point where there may be no benefit in some patients."
Redberg, who specializes
in
cardiovascular CT imaging, urged clinicians to carefully assess the benefits of
each CT scan and inform patients of the known risks
of radiation.
"In light of these data,
physicians [and their patients] cannot be complacent about the hazards of
radiation or we risk creating a public health time bomb," she wrote.
In the United States,
the total
number of CT (or computed tomography) scans performed annually has swelled from
3 million in 1980 to nearly 70 million in 2007, according to data cited by
Smith-Bindman's team.
CT scans combine computer
and X-ray
technology to produce detailed, cross-sectional images of the body that can
help clinicians diagnose and treat medical conditions.
However, because CT scans
typically
expose patients to a higher dose of radiation than conventional X-rays, the
dramatic rise in the use of this technology has become a reason for concern.
In fact, the new data
suggest that
its overuse may be doing more harm than good.
Watch the Video: X-Rays Reveal Unique Art
Smith-Bindman's team collected
data
from 1,119 patients who received 11 common types of CT scans performed at four
San Francisco-area hospitals. For each type of CT scan, the dose of radiation
varied widely within and across hospitals. There was a 13-fold variation, on
average.
"This kind of range had
been
reported before in CT scans of the heart, but putting it all together like this
for other types of CT scans is something which hasn't been appreciated
before," said Dr. Andrew J. Einstein, director of cardiac computed
tomography research at Columbia University College of Physicians and Surgeons
in New York City.
Because patients come
in different
sizes, some ability to vary the radiation dose is necessary to produce good
diagnostic-quality pictures, Einstein explained. But he found amounts of
variability in the study to be excessive.
The dose of radiation
for a
multiphase abdomen-pelvis CT study ranged from 6 to 90 millisieverts, and the
average dose was 31 millisieverts.
Ninety millisieverts,
depending on
how you count it, is equivalent to "many thousands of chest X-rays,"
Einstein said. "That's like the background radiation you and I would
receive over a 30-year period; it's just a tremendously high dose from one CT
scan procedure."
The number of CT scans
that would
lead to a case of cancer also varied by type of scan and the patient's age and
sex. For example, one in 270 women and one in 600 men who have a CT coronary
angiography at age 40 will develop cancer as a result. The risks were
approximately doubled for 20-year-old patients undergoing CT imaging. For
60-year-olds, the risks were 50 percent lower, the study authors noted.
In a separate analysis,
Amy
Berrington de Gonzalez, an investigator in the Radiation Epidemiology Branch of
the National Cancer Institute's Division of Cancer Epidemiology and Genetics,
projected future cancer risk from current CT use according to age, sex and scan
type.
Overall, her team estimated
that
29,000 future cancers could be related to scans performed in 2007, and that
these cases would result in about 14,500 deaths. The highest contributors to
those numbers are the scans most frequently performed, including abdomen and
pelvis, chest and head exams.
It's estimated that two-thirds
of
the projected cancers will occur in women, primarily because of the higher
frequency of use in women (60 percent) and because of higher breast and lung
cancer risks from scans that expose the chest.
While the numbers may
be scary,
Berrington de Gonzalez said people should realize "that CT scans provide
great medical benefits and that, in general, individual risks are small and
should be outweighed by the benefits if the CT scan is clinically
justified."
To ensure safe use, the
authors'
recommendations focus on reducing radiation dosages, eliminating unnecessary
and repeat examinations, and creating searchable electronic medical records to
collect and track CT studies over time.
"Although there is much
work to
be done, at this point this should be the agenda in radiology quality
improvement programs," said Dr. Richard T. Griffey, associate chief for
quality and safety in the Division of Emergency Medicine at Barnes-Jewish
Hospital and an assistant professor at Washington University School of Medicine
in St. Louis.
Clinicians also need more
information about patients' radiation exposures over time, he added. "We
have what can be a very fractionated health-care system, and doctors may not
know what studies their patients have undergone in their own institution, let
alone others, over their lifetime," he said. "While the incremental
harm of a single study may be impossible to really know, some sense for cumulative
radiation exposure would be valuable."
More information
The U.S. Food and Drug
Administration has more on CT scans.
SOURCES:
Rebecca Smith-Bindman, M.D., professor, residence, radiology, University of
California, San Francisco; Amy Berrington de Gonzalez, Ph.D., investigator,
Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics,
National Cancer Institute, Bethesda, Md.; Andrew J. Einstein, M.D., Ph.D.,
assistant professor, clinical medicine, and director, cardiac computed
tomography research, Columbia University College of Physicians and Surgeons,
New York City; Richard T. Griffey, M.D., associate chief, quality and safety,
Division of Emergency Medicine, Barnes-Jewish Hospital, and assistant
professor, Washington University School of Medicine, St. Louis; Dec. 14/28,
2009, Archives of Internal Medicine
Last
Updated: Dec. 14, 2009
