医院CT扫描或增加致癌风险

This is MORNING EDITION from NPR News. Sitting in for Steve Inskeep, I'm Ari Shapiro.

RENEE MONTAGNE, host:

And I'm Renee Montagne.

CT scans are commonplace in American medicine. A new study says they can also be dangerous. A group of researchers has found that patients commonly get too much radiation from these sophisticated X-rays, and some are predicting that radiation from CT scans will result in thousands of extra cancers in coming years. There's another development as well. Federal health authorities are investigating reports of dangerous radiation from CT scans at several hospitals in California and Alabama.

NPR's Richard Knox has the story.

RICHARD KNOX: It's not news that X-rays can cause cancer. But people thought the benefits from the amazingly detailed pictures produced by CT scanners far outweigh the cancer risk. Researchers of the National Cancer Institute and other institutions decided to estimate the risk from the 72 million CT scans done in this country in one recent year. Their answer: 29,000 people will get cancer because of the CT scans they had in 2007. Each year adds another 29,000 or more, at least until the radiation dose or the number of scans is cut. Dr. Rita Redberg is editor of the Annals of Internal Medicine, which is publishing the research. She calls the problem a public health time bomb.

Dr. RITA REDBERG (Editor, Annals of Internal Medicine): In 20-30 years, we're going to be seeing tens of thousands of excess cancers due to the increased radiation that people are incurring now.

KNOX: Another study in the journal drills down into the problem. It looks at the radiation doses patients are actually getting every day in four large San Francisco area hospitals.

Dr. REBECCA SMITH-BINDMAN (Radiologist, University of California): No one really appreciates the doses that are used in actual clinical practice and are much higher than we have thought and the variation in dose is dramatic.

KNOX: That's Dr. Rebecca Smith-Bindman of the University of California, San Francisco. She led that study. It finds that half the patients getting the most common CT scans to check for cancer, heart disease, strokes, blood clots in the lungs and so on are getting more radiation than they should, sometimes much more. Also, radiation doses varied enormously from one hospital to another and even within the same hospital for images of the same body part. Smith-Bindman says patients are getting so many scans because they expect their doctors to order them. Some people have even gotten whole body CT scans at malls just to make sure they don't have any health problems.

Dr. SMITH-BINDMAN: Patients definitely want imaging. They're entitled to imaging. And they don't appreciate that imaging, in fact, comes with this potential harm.

KNOX: But there's no doubt that doctors are mainly responsible for this skyrocketing popularity of CT scans. Dr. James Thrall is chairman of the American College of Radiology. He says there's a definite wow factor from CT scanning. It's a like a virtual tour of the patients' insides.

Dr. JAMES THRALL (American College of Radiology): Many of us sort of became hooked on ever better image quality before we came to the realization, the epiphany that it was the diagnosis that was important and not the quality of the image.

KNOX: Thrall says at his institution, the Massachusetts General Hospital, doctors who order a CT scan must list the reason. A computer program gives it a score, a low score indicates the test is probably unnecessary.

Dr. THRALL: Our experience over the past five years has been rather phenomenal. Before we instituted the system, the annual growth rate for CT scanning was 12 percent, a remarkable number. After we instituted a system, that dropped to one percent.

KNOX: Which is less than the growth in the hospital's patient load. In other words, now there are fewer scans for patient. Thrall thinks the claim that CT scans will cause 29,000 extra cancers a year is overstated. But whatever the number, he says...

Dr. THRALL: There are opportunities for us in the field of radiology to do all the good things we do using less radiation.

KNOX: He says scanner companies are working on machines that make good pictures using less radiation, but it will take years before the thousands of current machines are replaced. In the meantime, the College of Radiology and others are trying to figure out how to cut the radiation doses and the unnecessary CT scans that patients are now getting.

Richard Knox, NPR News.