Find Information About:

Drugs & Supplements

Get information and reviews on prescription drugs, over-the-counter medications, vitamins, and supplements. Search by name or medical condition.

Pill Identifier

Pill Identifier

Having trouble identifying your pills?

Enter the shape, color, or imprint of your prescription or OTC drug. Our pill identification tool will display pictures that you can compare to your pill.

Get Started
My Medicine

My Medicine

Save your medicine, check interactions, sign up for FDA alerts, create family profiles and more.

Get Started

WebMD Health Experts and Community

Talk to health experts and other people like you in WebMD's Communities. It's a safe forum where you can create or participate in support groups and discussions about health topics that interest you.

  • Second Opinion

    Second Opinion

    Read expert perspectives on popular health topics.

  • Community


    Connect with people like you, and get expert guidance on living a healthy life.

Got a health question? Get answers provided by leading organizations, doctors, and experts.

Get Answers

Sign up to receive WebMD's award-winning content delivered to your inbox.

Sign Up

Cancer Health Center

Font Size

Multiple CT Scans Raise Cancer Risk

Increase in Cancer Risk Is Small but Significant, Study Shows
WebMD Health News
Reviewed by Louise Chang, MD

March 31, 2009 -- As many as 7% of patients treated at a large U.S. hospital received enough radiation exposure from repeated CT scans to increase their cancer risk, according to a new study.

One in three patients included in the study from Harvard University’s Brigham and Women’s Hospital had undergone five or more CT examinations and one in 20 had more than 22 CT scans.

The findings confirm a modest but clinically significant increase in cancer risk associated with multiple CT scans, researchers say.

“We found that while most patients accrue small cumulative cancer risks, 7% of the patients in our study had enough recurrent CT imaging to raise their estimated cancer risk by 1% or more above baseline levels,” says lead researcher Aaron Sodickson, MD, PhD.

Use of CTs Growing

Approximately 68 million CT exams were performed in the United States in 2007, up from 62 million the previous year.

Unlike conventional X-rays, CT -- short for computed tomography -- provides a detailed, three-dimensional image of internal organs, which helps physicians diagnose and track the spread of disease.

“We know that many patients have multiple scans,” Sodickson says. “But we really haven’t had good information on the individual patient’s risk. That is what we tried to do in this study.”

Thanks to an electronic database, the researchers were able to track the CT histories of more than 31,400 patients who had a CT scan in 2007 at Brigham and Women’s Hospital or Harvard’s Dana-Farber Cancer Center.

They found that:

  • 5% of the patients in the study had received more than 22 CT scans, and 1% had received more than 38 examinations.
  • 15% of the patients had received estimated cumulative radiation doses that were higher than the radiation exposure from 1,000 chest X-rays.
  • 4% of patients had lifetime exposures equivalent to 2,500 conventional chest X-rays.

Using a cancer risk assessment model, the researchers found that 7.3% of the study participants had an elevated risk of cancer because of radiation from CT scans.

The risk was very small for most patients, totaling just 1% over the average lifetime risk of 42%.

But about 1% of the patients in the study had CT-related elevations in risk of between 2.7% and 12%.

“CT is an amazing diagnostic tool, and the last thing we would want to see is patients refusing needed scans because they are worried about cancer,” Sodickson says. “But patients and their physicians also need to be aware that there are risks and those risks add up over time.”

Today on WebMD

Colorectal cancer cells
New! I AM Not Cancer Facebook Group
Lung cancer xray
See it in pictures, plus read the facts.
sauteed cherry tomatoes
Fight cancer one plate at a time.
Ovarian cancer illustration
Real Cancer Perspectives
Jennifer Goodman Linn self-portrait
what is your cancer risk
colorectal cancer treatment advances
breast cancer overview slideshow
prostate cancer overview
lung cancer overview slideshow
ovarian cancer overview slideshow
Actor Michael Douglas