Pros and Cons of the PET/CT Scan
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/ Updated November 9th, 2020

Pros and Cons of the PET/CT Scan

Medical Source: Dr. Jakub Svoboda
Penn Medicine
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Why Combine PET and CT Scans for Lymphoma?

  • The PET/CT scan combines two tests in one for convenience and accuracy
  • A CT scan can find lymphoma in different areas of the body
  • The PET scan can distinguish healthy tissue from cancer
  • One risk is that the scan could find a cancer that isn’t there, called a false positive result
The PET/CT scan is a useful tool, both for diagnosing lymphoma and for tracking how well the cancer responds to treatment. The PET scan is especially well-suited to lymphoma, because it's more sensitive than CT scans alone at telling the difference between cancer and other types of abnormal tissues, such as scarring.

For example, a PET/CT scan can identify whether an enlarged lymph node or spleen is something to be concerned about. "As long as those areas are not metabolically active on a PET/CT, then we generally presume that those are just scars," Dr. Jakub Svoboda, medical oncologist at Penn Medicine, tells SurvivorNet.

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The PET/CT scan can provide some reassurance to people who might otherwise have had a worrisome finding on a CT scan alone. "As long as the PET scan shows no activity, we refer to that as a complete metabolic response. Those patients tend to do as well as if their CT scan was anatomically normal."

What is a PET/CT Scan?

The PET/CT scan combines two imaging tests in one. CT stands for computed tomography. It uses x-rays to take pictures inside the body from many different angles. A CT scan is helpful for locating lymphoma in areas like the belly, chest, pelvis, head, and neck.

PET is an acronym for positron emission tomography. It uses a radioactive form of sugar that cancer cells absorb more than healthy cells so it can help distinguish healthy cells from cancer. A PET scan can be useful for seeing how far the cancer has spread and determining its stage before treatment, and for finding small areas of lymphoma that wouldn't show up on a CT scan.

The PET scan is also useful for distinguishing lymphoma from other areas of abnormal tissue. Once you've started treatment, it can let your doctor know whether your treatment is working, or if you need to switch course. And if you've already finished treatment, it can show whether your cancer has returned and you need to start therapy again.

Combining PET with a CT scan can help doctors find areas of lymphoma better than either test alone.

The Risk of False Positives

The one downside to the PET/CT scan is that it can produce a false-positive result, meaning that the test shows you have cancer when you don't. The risk of having a false positive result is that you could get additional treatments that you don't actually need, with the potential side effects that come with those treatments. "The issue of false positives definitely is one of the shortcomings of this technology," Dr. Svoboda says.

"The PET/CT is great, but it doesn't have the perfect ability to distinguish between malignancy [cancer] or inflammation," he adds. And if you happen to see your radiology report and there is a questionable area, it could provoke a lot of anxiety. That lymph node could be lymphoma, but it also could be inflammation. "That makes it very scary for patients to read," Dr. Svoboda says.

This is where your doctor's expertise comes in. Doctors can look for other clues for example, whether you've recently gotten over a cold to determine whether the activity on your scan is cancer, or something benign, such as inflammation from an infection.

How to Make Sense of Your Test Results

The PET/CT scan is a good technology, but it isn't perfect. If you're concerned about your test results, or something pops up on your scan that worries you, have a discussion about it with the doctor who treats your cancer. You can also seek out a second opinion from an oncologist at another cancer center before making any changes to your treatment plan.

Learn more about SurvivorNet's rigorous medical review process.

Dr. Jakub Svoboda is a medical oncologist at Penn Medicine, and associate professor of medicine at the Hospital of the University of Pennsylvania. Read More

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