March 31 (HealthDay News) -- Cumulative exposure to radiation from CT scans can increase the risk for cancer by as much as 12 percent, Harvard University researchers report.
Widely used as a diagnostic tool, CT scans provide detailed images of organs, allowing more accurate diagnoses of conditions such as cancer. But CT involves a higher radiation dose than most other imaging tests.
"People should be aware that cumulative radiation risks do add up when they have numerous CT scans," said lead researcher Dr. Aaron Sodickson, assistant director of emergency radiology at Brigham and Women's Hospital in Boston.
Almost 69 million CT scans were done in the United States in 2007, up from 62 million the year before, according to a report from the Medical Information Division of IMV Ltd., a marketing research firm.
Generally, people should not worry about the risk of cancer associated with CT scans, Sodickson said. "Patients getting a small number of CT scans, they really shouldn't be very concerned at all."
However, people who are having a lot of CTs need to think more carefully and talk with their doctor to determine whether additional scans add value to their care because the risks can add up over time, he said. "We found cancer risks up to 12 percent" higher for people who had 38 scans, he said.
The report is published in the April issue of Radiology.
For the study, Sodickson's team looked at the medical records of 31,462 people who had undergone a total of 190,712 CT scans over 22 years. About 33 percent had five or more scans, 5 percent had more than 22, and 1 percent had more than 38.
In all, 15 percent of the people in the study had received cumulative radiation doses of more than 100 millisieverts (mSv), the same level of radiation as 1,000 chest X-rays. Four percent had received more than 250 mSv, and 1 percent had gotten more than 399 mSv.
For about 7 percent of the study participants, their cumulative radiation exposure increased their cancer risk by 1 percent above the U.S. cancer risk rate of 42 percent. For the 315 people who had received the most radiation, their risk of cancer increased 12 percent, the researchers calculated.
Dr. E. Stephen Amis Jr., chairman of the radiology department at Montefiore Medical Center in New York City, agrees that the dangers are there, but he said most patients should not be concerned.
"Patients should discuss with their physician," Amis said, suggesting they ask such questions as: "Do I really need this test? Have you considered the risk of radiation weighted against the benefit of the diagnostic acumen of the study?"
And if you really need the test, he said, you should have it.
"People should not be lying awake at night wondering when they are going to get their cancer -- after one or two or five or six CT scans -- if they needed to have them done," he said.
"On the other hand, if you have a chronic problem like passing kidney stones, and every time you show up at the emergency department every six months, they get another CT scan rather than doing a less-dangerous [test] that doesn't use radiation, like ultrasound, you are being mis-served, and CT is being overused," Amis said.
The results of Sodickson's study echo those of another study presented last May at the annual meeting of the Society for Academic Emergency Medicine.
In that study, researchers led by Dr. Timothy Bullard, chief medical officer and a practicing emergency room physician at Florida's Orlando Regional Medical Center, suggested that the long-term buildup of radiation from repeated emergency room X-rays and CT scans might be placing some people at an increased risk for developing cancer.
SOURCES: Aaron Sodickson, M.D., Ph.D., assistant director, Emergency Radiology, Brigham and Women's Hospital, Boston; E. Stephen Amis Jr., M.D., chairman, radiology, Montefiore Medical Center, New York City; April 2009, Radiology