Imaging Tests: Weighing the Radiation Risk

You walk into the emergency room, clutching your right side in pain. When the ER doctor examines your belly, she suspects you have appendicitis. But she wants to confirm the diagnosis before sending you for surgery. Or maybe your son falls off the high playground bars, and while he has a good-sized bump on his head, he seems otherwise fine. Should either of you have a computed tomography exam -- a CT scan? As with any medical test or procedure, there's a risk-benefit balance to consider.

Radiation Risk

Some 75 million CT scans are done each year in the United States -- and they're great diagnostic tools. A CT exam uses a specialized type of X-ray and a rotating scanner to take a variety of images from different angles around your body. CT exams rapidly produce clear, detailed, cross-sectional pictures. They facilitate diagnosis and treatment of trauma, cancers, cardiovascular disease, infections and congenital conditions, some life-threatening.

But the test itself may pose a health risk. CT scans use ionizing radiation, a known (although relatively weak) carcinogen. Research suggests that CT scans may raise cancer risk -- although it would still be very low -- particularly in childhood. In addition, studies find radiation doses used in CT vary widely among facilities, even for the same procedure on similar patients.

Rebecca Smith-Bindman, a physician and professor of radiology and biomedical imaging at the University of California--San Francisco, has published a number of papers on CT safety issues, dose variations and the notable rise in CT scans performed.

The increased exposure is a concern because of the high radiation dosage used, Smith-Bindman says: Compared to a standard chest X-ray, the radiation dose for a chest CT scan involves radiation that's 500 times higher or more.

Magnetic resonance imaging and ultrasound exams don't use ionizing radiation and are considered safer. MRI uses a magnetic field and high-frequency radio waves, while ultrasound uses sound waves to create images.

CT Conversation

Debra Ritzwoller of Colorado is the mother of a teenage cancer survivor. Her daughter, now 16, just marked her three-year anniversary of completing treatment for a rare solid tumor.

Ritzwoller, a health economist who does cancer-related research. was concerned about "surveillance" CT scans, used to monitor cancer survivors for relapse or recurrence. There's little evidence to support the effectiveness or value of regular surveillance CTs, Ritzwoller says. So she had a conversation with her daughter's oncologist. This led to her daughter's surveillance exams being switched from CTs to ultrasounds.

Don't hesitate to ask about alternatives, she advises, like using blood tests to monitor patients for cancer markers instead of (not in addition to) CT scans. "I would express concern about radiation exposure," she says. "That's a good way to start the conversation."

Smaller Bodies, Lower Doses

A 2012 study of British children showed evidence of a CT radiation-cancer link, and a 2013 study of U.S. children found having these tests in childhood brings a significant increase in risk of developing a cancer such as leukemia or a solid tumor.

Diana Miglioretti, a professor of biostatistics at the UC Davis School of Medicine and lead author of the U.S. study, found CT imaging "doubled in the younger kids and tripled in the older kids" over a 10-year period, after which the rate of usage stabilized.

A striking study finding was the large inconsistency in radiation exposure. "Children who get an abdomen CT can get a very different dose depending on where they go and who does the exam," she says. Because of their smaller size, children require lower radiation doses for CTs to produce diagnostic-quality images.

Based on current CT use and looking at the five most common pediatric CT exams performed combined -- of the head, abdomen, pelvis, chest or spine -- the researchers estimated that if about 4 million CTs were performed, that would cause 4,800 cancers.

The type of cancer was related to the body part on which the CT was done. For example, leukemia risk was highest for head CTs, especially for children under 5, Miglioretti says, because of the active bone marrow in their skulls.

Still, the risk for an individual patient of developing cancer from a CT radiation exposure "is very, very low," she notes. "So if the physician says an exam's medically necessary -- then yes, you should definitely do the exam."

Questions to Raise

If a CT is indicated, Smith-Bindman says, be explicit that you'd like that test done at the lowest dose possible -- with the doctor who's ordering it, the technologist who's doing it and the radiologist who's interpreting it. When deciding whether to consent to a CT for you or child, here's what to ask:

-- Is the test medical necessary? If so, do I need it now or can it wait?

-- Extent of the test: Are you doing the chest, abdominal and pelvis? Do you need all of those, or do you only need one?

-- Will my child receive the right dose for his or her size?

-- For cancer survivors, families may need to decide whether to do follow-up tests near home or stick with the children's hospital, Ritzwoller says. If so, ask: Will low-dose CT be available at the local hospital? Are radiologists well-versed in pediatric doses?

-- Is there an alternative test? Smith-Bindman, who just did a study comparing CT and ultrasound for spotting kidney stones, found the latter test was just as accurate.

-- Is it possible to do a single-phase rather than a multiple-phase CT exam?

-- To make an informed decision, Smith-Bindman says, ask the medical team: "Help me understand what the benefit is so I can balance it against the risk."

-- Besides asking if the exam is necessary, parents should also ask why it's necessary and whether the results will change the child's care, Miglioretti says.

Parents can also lower risk by avoiding repeat exams, she adds. "Sometimes when a child sees multiple physicians, they might repeat the exam. But the parent should always bring the other exam with them, and make sure a second test is really necessary if they've already had a CT," she says.

Proceed With Caution

For its part, the American College of Radiology points to studies from Germany and France that suggest the CT-cancer risk remains to be proved.

"According to recent French and German studies, it becomes clear that the direct cancer risk for solid tumors and lymphomas attributed to CT scans is not so accurate as some have claimed," says James Brink, vice chair of the ACR Board of Chancellors and radiologist-in-chief at Massachusetts General Hospital.

However, experts agree that while patients or parents should not hesitate to have a medically necessary CT scan, caution and standardization are needed.

"Recognizing the limits of epidemiological research does not mean medical radiation is not to be respected or scans done indiscriminately," Brink says. "Providers and patients should talk about benefits of medical imaging procedures. ACR just wants to ensure that up-to-date information is used in that discussion."

Safety Movement

Many groups are working to make CTs safer, standardize radiation doses among facilities and keep them as low as possible, use alternative methods when appropriate and avoid unnecessary scans.

As part of the Choosing Wisely initiative, organizations including the American College of Emergency Physicians, American Society of Clinical Oncology and American Academy of Pediatrics give guidance on when procedures such as CT scans should be avoided.

The Image Wisely initiative addresses radiation safety for adults. Image Gently, which focuses on children, provides information on imaging tests for physicians, radiologists, technologists and parents.

Lisa Esposito is a Patient Advice reporter at U.S. News. You can follow her on Twitter, connect with her on LinkedIn or email her at lesposito@usnews.com.