WEDNESDAY, Dec. 1 (HealthDay News) -- The risk of developing
cancer as a result of radiation exposure from CT scans may be lower
than previously thought, new research suggests.
That finding, scheduled to be presented Wednesday at the annual
meeting of the Radiological Society of North America in Chicago, is
based on an eight-year analysis of Medicare records covering nearly
11 million patients.
"What we found is that overall between two and four out of every 10,000 patients who undergo a CT scan are at risk for developing secondary cancers as a result of that radiation exposure," said Aabed Meer, an M.D. candidate in the department of radiology at Stanford University in Palo Alto, Calif.
"And that risk, I would say, is lower than we expected it to be," said Meer.
As a result, patients who need a CT scan should not be fearful
of the consequences, Meer stated.
"If you have a stroke and need a CT scan of the head, the benefits of that scan at that moment outweigh the very minor possibility of developing a cancer as a result of the scan itself," he explained. "CT scans do amazing things in terms of diagnosis. Yes, there is some radiation risk. But that small risk should always be put in context."
The authors set out to quantify that risk by sifting through the
medical records of elderly patients covered by Medicare between
1998 and 2005.
The researchers separated the data into two periods: 1998 to
2001 and 2002 to 2005. In the earlier period, 42 percent of the
patients had undergone CT scans. For the period 2002 to 2005, that
figure rose to 49 percent, which was not surprising given the
increasing use of scans in U.S. medical care.
Within each group, the research team reviewed the number and
type of CT scans administered to see how many patients received
low-dose radiation (50 to 100 millisieverts) and how many got
high-dose radiation (more than 100 millisieverts). They then
estimated how many cancers were induced using standard cancer risk
Yet despite the upward trend in the overall use of CT scans,
with an apparent doubling of both low- and high-dose radiation
exposure within the two time frames, the researchers determined
that there was a "significantly lower risk of developing cancer
from CT than previous estimates."
Cancers associated with radiation exposure were estimated to be
0.02 percent of the first group and 0.04 percent of the second.
Previous estimates ranged from 1.5 percent to 2 percent, said
While the results are good news, the consequences of CT scans
should continue to be monitored, the authors concluded.
Dr. Robert Zimmerman, executive vice chair of radiology at Weill
Cornell Medical Center in New York City, said that assessing CT
scan risk is a tricky endeavor. He believes patient needs should be
assessed on a case-by-case basis so as to limit exposure as much as
"It doesn't surprise me that the secondary cancer risk is low," he said. "But it's a very complicated epidemiological notion to deal with. Does every amount of cancer radiation exposure increase your risk, or is there a level of exposure that your body can always tolerate and recover from? It's very, very hard to say," Zimmerman pointed out.
"For better or worse we are now conducting an experiment on the entire population of the U.S. as to whether or not low-dose radiation exposure is going to raise risk of developing cancer," he said.
Reducing radiation doses across the board should be the goal,
regardless of the study's finding, he noted. "We always want to
make sure that the dose used when scanning is as low as possible,
and that scanning only takes place when necessary and beneficial to
the patient," he said.
Because this study was presented at a medical meeting, the
findings should be viewed as preliminary until they are published
in a peer-reviewed journal.
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