How Safe Are Imaging Scans?

If you need to have several of these tests over the course of your cancer treatment, it’s natural to wonder how that exposure might affect your future health. “A lot of our patients ask us, ‘What are the harmful effects of PET/CTs or imaging in general?'” Dr. Jakub Svoboda, medical oncologist at Penn Medicine, tells SurvivorNet.

“It’s true that I prefer not to do scans if I don’t have to do them,” he says. “That’s how I think most of us practice.” But, he adds, “The amount of radiation that patients get with each exposure to a CT scan or a PET/CT is so small that your body is able to tolerate it.”

Imaging Test Radiation Exposure: By the Numbers

Scientists measure radiation exposure with a unit called the millisievert (mSv). Most Americans are exposed to about 3 mSv of radiation from their environment each year.

Your level of radiation exposure differs, depending on which test you have. A single chest x-ray exposes you to about 0.1 mSv, which is a negligible amount. A PET/CT scan is a much bigger exposure, with about 25 mSv of radiation. That is equivalent to about eight years’ worth of environmental radiation exposure. However, Dr. Svoboda stresses that you’re not getting it all at once.

After the Chernobyl nuclear power plant disaster in 1986, workers were exposed to up to 170 mSv of radiation. Those who were exposed faced a significantly higher risk of thyroid cancer in the years that followed.

“It’s very different if you get exposed during an explosion at just one time, because your DNA gets damaged, whereas if you are exposed to radiation in small amounts at a time, such as via a PET/CT Scan, your DNA has the ability to repair and to fix things,” he says.

To Scan…Or Not to Scan?

“You need to be careful not to do too many scans, but in many situations the imaging is really essential for us,” Dr. Svoboda says. If your doctor is using an imaging test to find out if you have cancer and where in your body it is so that you can get started on the right treatment, it can be a lifesaving tool. In that case, the benefit of having the test outweighs any risk of radiation exposure.

Still, it’s important to use imaging tests judiciously. Every time your doctor says you need an x-ray, CT scan, or PET scan, find out why the test is being done, and what your doctor hopes to learn from it. Ask whether another test that uses less radiation (such as an x-ray) or no radiation (such as an MRI or ultrasound) could provide the same information.

Keep a record of every imaging test you’ve had, and share it with all of the health care providers you visit. And look for situations in which you might piggyback tests; for example, using one CT scan to diagnose two potential health problems at once.

Safer Scanning

Whenever you have an imaging test, ask the technician to use the lowest exposure setting and take the fewest number of pictures necessary to obtain the information your doctor needs. Also ask that they shield the parts of your body that aren’t being scanned. A lead apron can cover areas such as your chest and belly, while a lead collar shields your neck.

Pregnant women have special considerations when deciding to have an imaging scan. If you are pregnant, your doctor will weigh the risk of the test to your unborn child against the benefit of gaining more information about your cancer.

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