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For Patients, computed tomography ( CT ) scan can mean the difference between life and death, detecting a brain tumor, blood clot or burst appendix in seconds.

But federal regulators, radiology groups and hospitals are launching efforts to scale back use of the scans, also called CAT scans, amid growing evidence that they are exposing millions of patients to radiation that may elevate the risk of cancer in the future. A third or more of scans may be unnecessary or repetitive, studies show, and in scans that are medically appropriate, radiation doses could be dramatically reduced without hurting the quality of images.

Combining special x-ray equipment with sophisticated computers, CT - for computed tomography - produces vivid cross-sectional pictures of organs, bone, soft tissue and blood vessels with far greater clarity and detail than regular x-ray exams - but at 50 to 500 times the radiation dose. The number of CT scans in the U.S. has skyrocketed to about 70 million a year from just three million annually in 1980. A study in the Archives of Internal Medicine estimated that 29,000 future cancers could be related to CT scans performed in the U.S. in 2007 alone.

The Food and Drug Administration recently announced a broad initiative to reduce unnecessary radiation exposure from all medical imaging, and is developing new safety requirements for manufacturers of CT devices. It also said it will support "informed clinical decision making" programs that prompt doctors to think twice before ordering a scan whose risk may outweigh its benefit.

Dr. Brenner co-authored a study in the New England Journal of Medicine in 2007 estimating that 20 million adults and one million children are being irradiated unnecessarily and up to 2% of all cancers in the U.S. at present may be caused by radiation from CT scans, based on data extrapolated from atomic bomb survivors in Japan.

The American College of Radiology says equating the CT scans and atomic exposure is faulty, and that there is still no direct evidence linking CT scan radiation to cancer.

"Someone who comes in with a stroke could die today, but if they are worried about a cancer 30 years from now they may refuse a life-saving scan," says James Thrall, chairman of the American College of Radiology's Board of Chancellors and chief radiologist at Massachusetts General Hospital in Boston.

That said, Dr. Thrall says patients should ask doctors whether a scan is necessary, what the risks and benefits are, and whether there is an alternative test that doesn't use radiation such as ultrasound, which relies on sound waves, or magnetic resonance imaging, which uses powerful magnets and radio-frequency waves. The College is working on a national registry to the track the radiation dose that patients receive from CT scans nationwide, which will allow facilities to compare their rates to others.

Experts say that the best way to reduce the use of CT scans is to encourage doctors to follow guidelines developed by the American College of Radiology and others. Massachusetts General Hospital incorporated thousands of the guidelines into a program that requires doctors to enter information about a patient in the hospital's electronic medical records system before ordering a scan. If the need is questionable or another test might be more appropriate, doctors will get a yellow light. If a scan isn't recommended, it comes up red. A study of the program's use from 2004 to 2009 found that the rate of growth in outpatient scans fell to 1% a year from 12%, even though outpatient visits grew at a compound annual rate of nearly 5% over the same period.

Source: The Wall Street Journal

Discuss more about CT in the CT user group.