June 7, 2010 / 9:20 PM / 9 years ago

Q+A-What is the radiation threat from CT scans?

CHICAGO, June 7 (Reuters) - A number of studies in the past year have raised concerns that Americans are exposed to too much radiation from CT scans, increasing their risk of cancer. [ID:nN01116048]

Here are some questions and answers about CT scans:

Q: WHAT IS A CT SCAN?

A: CT, short for computed tomography, is an advanced type of X-ray that gives doctors the ability to see inside the body, in some cases eliminating the need for exploratory surgery. CT scanners take cross-sectional pictures of the body and a computer program assembles these into an image.

CT scans deliver more radiation than conventional X-rays. A chest CT gives patient more than 100 times the radiation dose of a typical chest X-ray. A CT scan of the abdomen is roughly equivalent to 400 chest X-rays. Too much radiation can cause skin burns, cataracts and other injuries, and in extreme cases, cancer and death.

CT scan use in the United States has grown sharply. About 70 million CT scans were done on Americans in 2007, up from 3 million in 1980.

Q: HOW MUCH RADIATION DO THEY GIVE?

A: Radiation, which is measured in millisieverts, from CT scans varies widely.

A study in December by Dr. Rebecca Smith-Bindman of the University of California, San Francisco, looked at the 11 most common types of diagnostic CT scans at four institutions in 2008. They found radiation dosage varied from a median or midpoint of 2 millisieverts for a routine head CT scan to 31 millisieverts for a scan of the abdomen and pelvis, which often involves taking multiple images of the same organ.

Q: HOW MUCH RADIATION IS TOO MUCH?

A: The average American receives about 3 millisieverts a year from ground radon or flying in an airplane. This level is not considered a risk to health.

Researchers say a radiation dose of 50 millisieverts starts to raise concerns about human health and a dose of 100 millisieverts is thought to raise the risk of cancer.

All of the studies estimating the risk from CT radiation exposure are based on the rates of cancer that occurred in people exposed to radiation from the atomic bombs dropped on the Japanese cities of Hiroshima and Nagasaki at the end of World War Two.

But many experts disagree over whether that model offers a fair comparison. Meanwhile, imaging equipment makers such as GE Healthcare (GE.N), Siemens (SIEGn.DE), Philips (PHG.AS) and Toshiba Medical Systems (6502.T) are working to develop low-dose CT scanners.

Q: HOW DO PATIENTS BECOME OVEREXPOSED TO RADIATION FROM A CT SCAN?

A: This can happen in two ways. Accidental overdoses can occur when CT equipment settings are improperly programmed or technicians running the machines make an error.

These kinds of accidents are rare. To prevent them, the U.S. Food and Drug Administration has asked the top makers of CT scanners to add safeguards to their machines.

The Medical Imaging & Technology Alliance says manufacturers will add a color-coded warning system to give healthcare providers clear warning when scans could harm patients. These changes are being phased in later this year.

The American College of Radiology has called for an accreditation program for facilities that deliver radiation therapy to cancer patients, something the medical equipment industry group AdvaMed supports as a way to enhance patient safety.

Repeated CT scans can also pose a risk as the cumulative radiation dose builds over time.

Researchers are working on new computer programs that help doctors make better decisions about whether a CT scan is the best way to diagnose a condition. Equipment manufacturers are developing software that allows radiologists to use a much lower dose of radiation while still producing a sharp picture. (Editing by Maggie Fox and Bill Trott)

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