Radiation Risks Of Full-Body Scans
Posted by medconsumers on October 1, 2004
Full-body scans have been heavily promoted to the public as a means of finding cancer before symptoms appear, but a new report suggests that the radiation doses delivered by these tests are high enough to cause cancer. In last month’s issue of the journal Radiology, David J. Brenner, PhD, and Carl D. Elliston, MA, provided the following lifetime estimates of the risks associated with having one or repeated full-body scans.
“If a 45-year old adult has one screening full-body scan, then many years down the line, one in 1,200 will die from a radiation-induced cancer,” explained Dr. Brenner, in a telephone interview. He noted that this risk is obviously low, but the promotion of these full-body scans as screening tests means that symptomless people are encouraged to accept regular testing.
“A screening test is only going to be useful,” he said, “if it is given annually or biannually.” Then the odds of cancer mortality become much higher. “If a 45-year-old has annual full-body scans until the age of 75 years, then one in 50 will die of a radiation-induced cancer,” estimates Dr. Brenner, who is a radiation biologist, that is, a specialist in the health effects of radiation on the human body. For anyone who starts the same regimen at age 60 years, the odds of a radiation-induced cancer death would be one in 220.
Brenner and Elliston based the estimates of lifetime cancer death risk on the atomic bomb survivors from Hiroshima and Nagasaki who had been exposed to the lowest amounts of radiation. The doses received by these survivors are comparable to those received from full-body scans.
The use of computed tomography, or CT scans, for symptomless people is relatively new. In addition to searching for early-stage cancers, heart scans for calcium in the coronary arteries are also heavily advertised to consumers. Most people undergo screening heart or full-body CT scans at freestanding clinics run by entrepreneurial radiologists, and the $300 to $1,000 cost is usually paid by the consumer. Insurance companies and managed care plans typically do not reimburse for screening CT scans because their benefit is yet to be proven. Furthermore, screening scans lead to false alarms and unnecessary, sometimes risky, testing and biopsies.
There are no statistics regarding the number of people who undergo screening CT scans each year, but there has been a dramatic increase in the number of freestanding CT scan clinics since 2001. Because radiation’s harm is cumulative, there have always been questions surrounding the safety of scanning people without symptoms. Brenner and Elliston are the first to quantify the radiation exposure.
A full-body scan means radiation is delivered from the chin to just below the hips. “The reason for the high radiation dose is that the machine fires in beams of x-rays from different directions providing 3D images—that’s why it’s called computerized tomography,” explained Dr. Brenner. “The patient is getting many separate x-rays. And that’s why the doses are much higher than those from conventional x-rays.”
Dr. Brenner made a distinction between the use of CT scans as a screening method and their use in diagnosing illness in a person with symptoms. The benefit of receiving the correct diagnosis outweighs the radiation risk. “If, say, a person has lung symptoms, the radiation dose [from the lung scan] goes only to that organ plus a small dose to the stomach because x-rays scatter.” But full-body scans are imaging the main organs of the body so they give a significant radiation dose to all those organs.
Unfortunately, it has always been difficult to find honest information about the radiation risks of medical tests. Radiologists have traditionally dismissed medical radiation exposure concerns. A recent survey indicates that physicians who order CT scans may be the least likely to be knowledgeable about radiation risks. Last May, a Yale survey of radiologists and emergency room physicians found that most of them did not believe that scans could increase the risk of cancer.
It is unusual for a medical group or a federal agency to come out a against screening test, but the American College of Radiology does not recommend full-body screening scans and the American Heart Association* does not recommend screening heart scans, citing concerns about the lack of proven benefit and the risks of overtreatment. Neither is explicit about the radiation risks; but the U.S. Food and Drug Administration (FDA) is a notable exception.
On its Web site, the FDA Center for Devices and Radiological Health comes right out and states that the use of CT scans to screen symptomless people has “no proven benefit.” To help people understand the amount of radiation involved, the agency has a radiation dose comparison chart showing, for example, that the radiation received by a CT scan of the abdomen is the equivalent of 500 chest x-rays.
The scans won’t give you peace of mind (a typical selling point), according to the FDA Web site, because a normal finding may erroneously be identified as cancer or a “clean bill of health” may be inaccurate. One would hope there was some independent oversight. Here too, the FDA is explicit about what it does not have the authority to do: “The FDA does not establish dose limits, nor does it address the imaging performance or efficacy of the CT equipment.”
For More Information:
Go the Web site of the FDA Center for Devices and Radiological Health.
To read why the U.S. Preventive Services Task Force is against the use of screening heart scans for calcium in the coronary arteries, go to www.ahrq.gov/clinic/uspstf/uspsacad.htm.
Read these two 2009 articles: one about the excessive amount of radiation associated with CT scans and the other about the radiation dose involved in cardiac CT scans.
Maryann Napoli, Center for Medical Consumers ©