CT radiation exposure

CT Scan Radiation Risks? Aug. 31, 2004/ (WebMD) \

also see the study in NEJM here

They promise to cut your risk of dying from cancer. Yet full-body CT scans themselves pose a real cancer risk, new calculations suggest. X-rays from a single full-body CT scan give a dose of radiation similar to cancer-associated radiation doses in A-bomb survivors, finds David J. Brenner, PhD, director of Columbia University's center for radiological research. It's not a huge risk, especially for someone with symptoms of a dangerous condition. But when used to screen healthy people for hidden evidence of disease, the risk may outweigh the benefit. And if a healthy person gets repeated full-body scans, cancer risks multiply, Brenner and colleague Carl D. Elliston report in the September issue of Radiology.

"The risks from a single full-body CT scan are not large: If 1,200 45-year-old people got one, you might expect one to die from radiation-induced cancer," Brenner tells WebMD. "But if you are thinking of doing this on a regular basis, as a routine screening modality, then the radiation doses start to add up and the risks then start to get quite high." A single full-body CT scan gives a person a total radiation dose of about 12 mSv. That's close to the 20-mSv dose linked to cancer in Japanese survivors of atomic bombs. And each of these scans adds another 12 mSv to a person's total lifetime exposure. An mSv is a unit for measuring radiation dose.Studies suggest that full-body CT scans aren't likely to benefit anybody under the age of 45. This led Brenner to calculate cancer risk for someone who decided to have annual full-body CT scans beginning at that time. "If you start at age 45, and have them annually until you are 75, you are talking about a one-in-50 chance of radiation-induced cancer, which is a huge risk," Brenner says. "Until the benefit is clear, there is not much of an advantage to having routine body scans yearly or even every two years. But a single scan is not much of an issue."

Electronic Checkups

For several years now, freestanding clinics have been offering full-body CT scans to anyone who wants one. Ads for the clinics promise early detection of dangerous diseases such as cancer and heart disease. The idea is that full-body CT scans will find tumors other signs of disease in their earliest, most treatable stages -- before a person has any symptoms of illness."The idea is to replace annual physicals with this noninvasive test, which might detect things you wouldn’t usually see -- like a small tumor, or the beginnings of heart disease," he says. "It has the potential for seeing things -- mainly cancers -- rather earlier than they might otherwise have been detected."

James P. Borgstede, MD, chairman of the American College of Radiology's board of chancellors, notes that the ACR does not sanction the use of full-body CT scans for screening healthy people. He notes, however, that the ACR doesn't censure doctors who perform the procedure.
"I think the people who get these scans are the worried well," Borgstede tells WebMD. "They are very concerned about health but tend to be very safe, low-risk people. They think they will live longer or have a better-quality life if they get these scans, I guess. But there is no data that support they will live longer or better if they have one of these exams."

Richard L. Morin, PhD, chairman of the ACR's commission on medical physics, says that given lack of an established benefit, the risks Brenner identifies raise doubts about screening healthy people with full-body CT scans.
"This paper is important in demonstrating explicitly that the risk from whole-body CT or any other diagnostic radiology exam is not zero," Morin tells WebMD. "It supports the thinking that screening whole-body CT scans of healthy individuals is not a wise course of action."

Borgstede and Morin note, however, that the risk/benefit equation changes for patients with symptoms who need CT scans to help diagnose a disease. These patients' symptoms usually tell the doctor that a particular part of the body should be scanned. Full-body scans, Borgstede says, usually aren't needed.
"We support clinical trials of CT screening for lung and colon cancer -- but those are studies of selected populations we think may be at risk of very serious disease," he says. "That is different from screening the whole population from head to toe. These screenings are planned only for the body area at risk."