CT Scans May Pose Less Cancer Risk Than Thought, Study Contends

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CT Scans May Pose Less Cancer Risk Than Thought, Study Contends

By Alan Mozes

HealthDay Reporter by Alan Mozes

healthday Reporter Wed Dec 1, 11:48 pm ET

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 models.

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 the authors.

While the results are good news, the consequences of CT scans should continue to

be monitored, the authors concluded.

Dr. 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 possible.

" 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.

More information

For more on CT scans, visit radiologyinfo.org.