What Is a PET Scan, and How Is It Used in Prostate Cancer?

When cells in the prostate grow out of control, prostate cancer develops. Prostate cancer is a leading cause of cancer in the U.S. Healthcare professionals have many tools to evaluate prostate cancer. One tool is the PET scan. 

If you need a PET scan, here’s everything you need to know about how PET scans work and what you need to do to prepare for yours. 

What is a PET scan?

A positron emission tomography study — or PET scan — is a type of imaging study. During a PET scan, you take a small amount of radioactive material, called a “tracer.” The tracer is very safe because only a tiny amount is used. 

There are many types of tracers. But two new tracers are more common than the rest. These tracers stick to a protein that’s only found on prostate cancer cells. Once it’s stuck to the prostate cancer cells, it gives off energy. Cameras can capture this energy, which healthcare professionals can then see on images. When you get a PET scan, you can actually see where the cancer cells are in your body. 

When do you need a PET scan for prostate cancer?

You may need a PET scan during your prostate cancer treatment for several reasons, including:

• Staging: Not all prostate cancers are the same. In some cases, a biopsy or other test result reveals that the prostate cancer could move outside of the prostate. If this is the case, a PET scan can tell how far the cancer may have advanced. Staging shows how much cancer is in the body, which can affect treatment decisions.

• Metastasis: PET scans can look for new metastases, or areas where the cancer has spread. Newer PET scans — called “PSMA PET scans” — are more accurate for detecting metastatic prostate cancer. They can find evidence of metastases earlier, which means you can get treatment sooner.

• Response to treatment: Once you start treatment for prostate cancer, you may need a PET scan, a prostate-specific antigen (PSA) test, and others to make sure your cancer is responding to treatment.

• Monitoring for recurrence: After you finish treatment, you’ll have regular follow-ups to look for any signs of recurrence. If there’s concern that your prostate cancer has returned, you may need a PET scan to look for new cancer cells. 

What should you expect during a PET scan for prostate cancer?

There’s not much you need to do to prepare for your PET scan. Depending on the type of tracer you’re getting, you might need to do the following:

• Avoid eating or drinking anything for 6 hours before your scan. But you can drink water and take routine medication.

• Eat high-protein, low-carbohydrate foods for your last meal before the scan. 

• Avoid exercise for 24 hours before the scan.

The newer tracers that are specific for prostate cancer don’t require any of these restrictions. So, if you’re having a PSMA PET scan, you won’t need to stop eating, drinking, or exercising. Your healthcare team will confirm what restrictions you may need.

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What to expect the day of your scan

The day of your PET scan, here’s what to expect:

• You’ll check in and be asked some basic questions. Let the team know about any medications you take and if you have any allergies. 

• A healthcare professional will insert an IV line, usually in your arm. 

• You’ll be given the tracer through the IV. You might feel some coolness as the tracer moves into your arm — this is normal. Allergic reactions to the tracer are very uncommon.

• It takes about 60 minutes for the tracer to stick to the cancer cells. Depending on the type of tracer you get, you’ll be asked to lie down during this time and not walk around. Moving around can affect how the tracer gets distributed in your body. 

• After the waiting period, you’ll get your pictures taken. You’ll be asked to lie on the imaging table and remain still for about 20 to 40 minutes. 

• You won’t feel any pain while you're having the pictures taken. But if you have pain when lying on your back, let your healthcare team know. They can prescribe medication to keep you comfortable during the scan.

• During the PET scan, you’ll be in an enclosed space. If enclosed or tight spaces make you anxious, let your healthcare team know before your exam. They can order medication to make you more comfortable.

After your PET scan

After the scan is over, you’ll have a small amount of tracer left in your body. You can drink a normal amount of fluid to flush the tracer out of your body. It’ll come out in your urine and stool over the next 24 hours. The amount of tracer you got was very small. You won’t need to stay away from friends or loved ones after the scan. 

Side effects of PSMA PET scans

PSMA PET scans are considered very safe. As with all medical tests and medications, there are potential side effects from getting a PET scan. 

• A mild reaction to the injection

• Allergic reaction to the tracer, especially in people who have allergies to other tracers

• Temporary discomfort like headache, tiredness, or nausea

• Feeling claustrophobic in the scanner

Why PSMA PET scans are useful

PSMA PET scans are useful because they specifically look for a protein that's only found on the outside of prostate cancer cells. This type of “marker” is powerful because it offers:

• High sensitivity: PSMA can detect very small clusters of cancer cells anywhere in the body. When coupled with an MRI, it’s even more sensitive.

• Improved accuracy: Compared to a PSA blood test, PSMA scans are able to accurately locate the exact location of prostate cancer cells.

• Early detection: PSMA PET scans allow cancer to be detected earlier. Early detection is very important for aggressive tumors and for recurrences.

• Targeted treatment: PSMA PET scans can show exactly where cancer cells are located, even when they’ve spread outside the prostate. Knowing where cancer is located allows healthcare professionals to target treatments such as radiation, surgery, and chemotherapy for an individual patient’s needs.

How accurate is a PET scan for prostate cancer?

The PSMA PET scan is extremely good at detecting the presence of prostate cancer. A recent study showed an overall accuracy of about 92%. PSMA PET scans are the most sensitive and accurate tools to assess prostate cancer. 

PET scans aren’t perfect though. They can miss a small number of cancers, such as those that:

• Haven’t grown large enough to detect 

• Don’t make protein found on the outside of prostate cancer cells

Rarely, PET scans can also show an abnormal signal where there’s no cancer present.

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Written by:

Brian Clista, MD

Dr. Clista is a board-certified pediatrician who works in private practice in Pittsburgh, Pennsylvania. He previously served as a National Health Service Corporation Scholar in the inner city of Pittsburgh for 11 years.

Edited by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

Reviewed by:

Frank Schwalbe, MD

Frank Schwalbe, MD, is an assistant professor of anesthesiology at the Yale School of Medicine. He has practiced anesthesiology for 30 years.

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