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Image Lightly: BIDMC Takes Steps to Reduce CT Scan Radiation Exposure

CT Scan

CT scans are a valuable tool to help doctors diagnose injuries or detect illnesses such as cancers. They can also help in the planning of treatments of such injuries or illnesses. But they are not without risk.

Also known as computed tomography, CT scans combine a series of X-rays taken from a variety of different angles to produce cross-sectional images of the bones and soft tissues inside the body.

But X-rays expose patients to radiation. CT scans expose patients to even more radiation than do X-rays. Much more. For example, a typical CT scan of the chest can be the equivalent of 70 chest X-rays and a CT scan of the abdomen equivalent to 10 plain X-rays of the abdomen. Studies have suggested that CT scan usage may result in some 29,000 new cases of cancer each year in the U.S. alone.

But radiologists at Beth Israel Deaconess Medical Center and elsewhere are now taking actions to reduce the amount of radiation to which CT scan patients are being exposed.

"The amount of radiation to which patients are exposed is not insignificant," says Dr. Vassilios Raptopoulos, Director of CT and Vice Chair of Clinical Services at BIDMC and Professor of Radiology at Harvard Medical School.

"We really don't know the biological effect of a CT scan, but we do know that it has to be done prudently," he says. "We have to be careful." Studies have shown a wide range of radiation dose from scanner to scanner for the same exam.

The answer at BIDMC is a program called "Image Lightly," which is based on the ALARA principle (as low as reasonably achievable) and includes steps to reduce radiation exposure by individualizing the way of scanning according to the specific clinical indication in certain cases, keeping patients in the scanners for less time in other cases, or scanning less frequently if possible.

"For instance, if you are scanning someone who is suspected to have pancreatic cancer, you can scan differently than if you suspect appendicitis," he says.

"Many times you have to scan again and again in different phases, but we can sometimes reduce the number of phases," he says.

In certain cases, the amount of time the patient has to be in the machine can be reduced, he notes. And the radiation dosage may be able to be reduced depending on the size of the patient, he says.

Steps are also taken to make sure scans are not repeated unnecessarily, Dr. Raptopoulos says. For example, if a patient comes into the hospital through the Emergency Department and a scan is taken there, doctors are automatically notified so they don't order another scan to look at the same thing.

Doctors are also automatically notified of the number of scans each patient has already had that year.

In addition, doctors seek to obtain prior scans that may have been taken at referring hospitals so they don't have to do them over again.

On top of those steps, the hospital makes sure to check the scanners' settings frequently, sometimes daily, to make sure there is no radiation leakage, "so that it delivers what we want it to," he says. And with continuing upgrades the scanners can produce high quality images with less radiation. Overall, the radiation reduction strategies that have been implemented at BIDMC in the last few years have resulted in 30 to 50 percent reduction in radiation exposure.

"The CT scan remains a very useful diagnostic tool," Dr. Raptopoulos says. "Although I have never seen a case of cancer that was the result of a CT scan, we still must be careful. Eventually, we will probably turn to the use of MRI (Magnetic Resonance Imaging) more often, but there are issues with that machine too."


MRI does not expose patients to radiation. Instead, it uses a powerful magnetic field, radio frequency pulses and a computer to obtain images.

But MRI is still much more expensive than a CT scan, costing up to twice as much to perform. They also take longer to do and require patients to stay inside the machine longer. And while MRIs are better for imaging certain body parts, they are not as good for others, such as lungs, for example. There are also people who cannot receive an MRI, such as those with certain implants such as pacemakers.

Above content provided by Beth Israel Deaconess Medical Center. For advice about your medical care, consult your doctor.

Posted January 2011