A PSMA PET scan is an imaging test that detects prostate cancer anywhere in the body. This test is most often used to look for prostate cancer that spreads or comes back after treatment.

A PSMA PET scan is one kind of positron emission tomography scan, also called a PET scan. A PET scan uses a radioactive tracer to find specific cells in the body. The tracer is injected into a vein in the arm, and then it moves through the body. A camera in the PET scanner detects the places where the tracer builds up in the body.

In a PSMA PET scan, the tracer has a substance that helps it stick to cells that make PSMA. PSMA stands for prostate-specific membrane antigen. PSMA is a protein that's typically found on the surface of healthy prostate cells. When prostate cells turn into cancer cells, they often continue to have PSMA.

The tracer also contains a small amount of a radioactive substance. When a healthcare professional puts the tracer into a vein, the tracer travels through the body. The tracer sticks to the PSMA on prostate cancer cells and releases the radioactive substance. The PET scanner has a camera that detects the radiation. The camera is connected to a computer that makes pictures that show places in the body where the tracer builds up. A buildup of PSMA PET tracer might be a sign of prostate cancer.

Types of PSMA PET scans

All PSMA PET scans use tracers to find cells that have PSMA on their surfaces. But there are some different ways of doing the test. Differences in types of PSMA PET scans include:

• Types of radiation sources. Most PSMA PET tracers use radiation from gallium-68, also called Ga-68, or fluorine-18, also called F-18. The main differences between these radiation sources are how they are made and how long they continue to give off radiation. A tracer made with F-18 lasts a little longer than one made with Ga-68.
• Types of ligands. A ligand is a substance in the tracer that finds the specific cells. In a PSMA PET scan, the ligand sticks to the PSMA on prostate cancer cells. Examples of ligands used in PSMA PET scan tracers include flotufolastat, piflufolastat and gozetotide. Gozetotide also is called PSMA-11.
• Types of anatomical imaging. A PSMA PET scan is usually combined with another imaging test that shows the bones and organs in the body more clearly. Most often this is a computerized tomography scan, also called a CT scan. Sometimes the other test is a magnetic resonance imaging scan, also called an MRI scan. PET combined with MRI is new and not available at all hospitals. Combining PSMA PET with CT or MRI makes it easier to see exactly where the tracer builds up in the body.

A PSMA PET scan looks for prostate cancer that spreads in the body. This imaging test also can detect cancer that comes back and help with choosing a treatment.

Prostate cancer that spreads

A PSMA PET scan is sometimes used when prostate cancer is first diagnosed. It might be used if there's a risk that prostate cancer has spread beyond the prostate. Prostate cancer that spreads is called metastatic prostate cancer. It also is called stage 4 prostate cancer. Most people with prostate cancer have cancer only in the prostate, so they don't need this test.

A PSMA PET scan is one of many tests that can look for signs that the cancer has spread. Other imaging tests include bone scans, CT scans, MRI scans and other types of PET scans.

The test or combination of tests that is best for you depends on your situation. To choose a test, your healthcare team considers your overall health, your symptoms and the results of tests on your cancer cells. The care team also might consider which tests are available in your area. Not every hospital has every test. In the United States, the choice of test also might depend on which ones your health insurance covers.

Prostate cancer that comes back after treatment

If you had treatment for prostate cancer and have signs that the cancer is back, a PSMA PET scan might be used to look for the cancer. Prostate cancer that comes back after treatment is called recurrent prostate cancer.

Often a rising level of prostate-specific antigen, also called PSA, in the blood is the first sign of recurrent prostate cancer. If a blood test shows elevated PSA levels, your healthcare professional might recommend imaging tests to look for the cancer.

Imaging tests might look for signs of recurrent prostate cancer near the prostate or where the prostate used to be if it was removed with surgery. Often the imaging test is an MRI scan of the pelvis.

Some tests look for prostate cancer in the bones. Examples of tests that look for cancer only in the bones include a bone scan and a sodium fluoride F-18 PET scan.

Other tests look for prostate cancer all over the body. These tests include the PSMA PET scan and other PET scans, such as the choline C-11 PET scan, fluciclovine F-18 PET scan, and fluorodeoxyglucose F-18 PET scan, also called FDG PET scan.

There are many imaging tests that can help detect recurrent prostate cancer. To pick a test, your healthcare team considers your PSA levels, your symptoms, your overall health and which prostate cancer treatments you had. Your care team also might consider what tests are available in your area and which tests your insurance covers.

Prostate cancer treatment

The results of a PSMA PET scan can help the healthcare team decide on a treatment. The results might be used to decide on treatment for a metastatic prostate cancer that no longer responds to hormone therapy treatment. This kind of prostate cancer is sometimes called metastatic castration-resistant prostate cancer.

If a PSMA PET scan shows that the tracer builds up in the prostate cancer cells, this is a sign that treatment with PSMA therapy may help treat the cancer. If the tracer doesn't build up in the cancer cells, then PSMA therapy isn't likely to treat the cancer.

PSMA therapy uses a medicine that contains a substance that finds and sticks to the PSMA on prostate cancer cells. The medicine also contains a radioactive substance that can kill cancer cells. A healthcare professional gives this medicine through a vein. The medicine finds prostate cancer cells and releases radiation directly into the cells.

A PSMA PET scan is a safe imaging test. Like all tests, it has some risks, limitations and side effects. These include side effects related to the tracer that goes into your arm before the scan. Other risks include exposure to radiation and getting results that aren't clear.

Side effects of the tracer

A PSMA PET scan uses a tracer. The tracer is a substance that helps show areas of prostate cancer on the PET scan images. A healthcare professional puts the tracer into a vein in your arm. There can be some side effects related to injecting the tracer, including:

• A mild reaction to the injection. There might be slight pain and skin irritation at the place where the tracer goes into your arm.
• Allergic reaction to the tracer. This is rare and usually mild. Most often an allergic reaction causes hives and itching. Very rarely it can cause difficulty breathing or a life-threatening reaction.
• Other side effects. Other rare side effects include nausea, vomiting, constipation, diarrhea, headache and feeling very tired.

Exposure to radiation

The PSMA PET scan exposes you to radiation from the tracer. This test often also includes a CT scan at the same time. A CT scan uses X-rays to make images. The CT scan also exposes you to radiation.

The amount of radiation is considered safe. Your healthcare team carefully weighs the risks of radiation from the combined PET-CT scan against the benefits of getting an accurate diagnosis.

The exact amount of radiation depends on your situation. Generally, the radiation you're exposed to during a combined PET-CT scan is the same as about seven years of natural radiation. Natural radiation, also called background radiation, is the radiation that comes from the Earth and the sun. Everyone gets a low level of radiation from these natural sources.

Results that aren't clear

A PSMA PET scan is an accurate test. But it's possible for the PSMA PET scan to have results that aren't clear.

• False-negative result. A false-negative result can happen if cancer is present, but the test doesn't find it. Some prostate cancer cells don't make PSMA. They aren't detected on this test. A false-negative result also could happen if the prostate cancer cells are in an area that's hard to see on the PSMA PET scan. For example, the tracer often builds up in healthy cells in the kidneys. This can make it hard to see prostate cancer cells that spread to the kidneys.
• False-positive result. A false-positive result can happen if the scan detects something that looks like cancer, but further testing finds that it isn't cancer. If your scan finds something concerning, you might have other tests and procedures to see if it is cancer. This might involve other imaging tests or a procedure to remove some cells for testing, called a biopsy.
• Finding other cancers. It's possible for a PSMA PET scan to detect other kinds of cancer, but this is very rare. Some other types of cancer that have been found on PSMA PET scans include lymphoma, lung cancer, liver cancer, bladder cancer and brain tumor.

If your healthcare team gives you instructions to help you prepare for a PSMA PET scan, follow them carefully. You may be asked to drink plenty of liquids, such as water, for a few hours before the test. Generally, you can eat and take medicines as usual before this test unless you are told something different by your care team.

Before your PSMA PET scan, tell your healthcare team:

• About any medicines you take, including medicines that you can buy without a prescription, as well as any vitamins or supplements that you take.
• About any allergies or bad reactions you've had to any medicines, foods, iodine or latex.
• About any metal or devices in your body. Examples include implanted medical devices, such as a pacemaker, and foreign metal objects, such as bullet fragments and body piercings.
• If you've ever felt afraid of being in small spaces, also called claustrophobia. Some people feel this way during imaging tests. Medicine can help you feel more at ease during the test.

Wear comfortable clothing to your appointment. Check that your clothing has no metal on it. If there is any metal on your clothing, you may be asked to change into a gown. Before the scan, you will be asked to remove all metal from your body including jewelry, glasses and dental retainers.

If you drive, you should be able to drive yourself to and from your appointment. Someone may go with you to the appointment, but that person will have to stay in the waiting room.

If you might receive medicine to help you feel at ease during the test, you may need someone to drive you to and from your appointment. Ask a care team member about this before your appointment.

During a PSMA PET scan, you receive an injection in your arm and then have an imaging test. The process typically takes about two or three hours. After the test, you can go about your day as usual.

Before a PSMA PET scan

Before a PSMA PET scan, a healthcare professional puts a radioactive tracer into a vein in your arm. The tracer contains a substance that sticks to cells that have PSMA on the surface. The tracer also contains a small amount of a radioactive substance.

You might feel a pinch as a healthcare professional puts a needle into a vein in your arm. This usually doesn't hurt. Your arm might feel cold as the tracer goes in. Rarely, an allergic reaction to the tracer can happen. Your healthcare team watches carefully for this reaction. Most allergic reactions are mild ones that cause hives and itching.

After receiving the tracer, you may wait about an hour before you have the imaging test. You may stay in a quiet, dimly lit room during this time. You may be asked to rest on a recliner or bed. Your healthcare team may ask that you not watch TV, read or use any electronic devices during this time.

After the tracer has had time to move through your body, you'll go to another room for the imaging test. You may be asked to empty your bladder before the scan begins.

During a PSMA PET scan

Next, you'll have an imaging test. For a PSMA PET scan, the test usually includes a PET scan and a CT scan. The same machine typically does both scans.

You lie down on a cushioned table. Then a healthcare team member positions you comfortably with your arms over your head and secures your body to the table with straps. The table rises and moves into the scanner. The scanner is a large, round machine with a big hole in the middle through which the table slides.

You must be still and quiet during the scan. The scan usually lasts about 30 to 60 minutes. Staying still for a long time in one position can cause some discomfort.

The scanner takes images of most of the body. For a PSMA PET scan, the scanner typically takes images from the upper legs to the head. This is considered a whole-body PET scan.

After a PSMA PET scan

After the PSMA PET scan is done, you rest for about 10 minutes while your healthcare team checks the scans. The team reviews the scans to ensure no more scans are needed. Once your healthcare team decides you are done, you can leave and go about your day.

Your healthcare team might tell you to drink water and empty your bladder frequently for the rest of the day after the test. This helps clear the tracer from the body.

After the PSMA PET scan, you might be concerned about:

• Driving. It's safe to drive and to go back to work, if you choose, after the PSMA PET scan. But if you received medicine to help you feel more comfortable during the scan, it may not be safe to drive. You will need someone to take you home.
• Flying. The radioactive tracer stays in your body for about 24 hours. If you fly during this time, you may set off radiation detectors used by airport security. If you plan to fly, ask your healthcare team for a card you can show to security. The card states that you had the PSMA PET scan.
• Side effects. You may have minor soreness at the place where the tracer was put into your arm. It should go away in a few days. If you have swelling at the site, contact your healthcare team right away.
• Diet and activity. Unless you are told something else, you may resume your usual diet and activities, as you feel able. Drink extra fluids to keep your body well hydrated. For the rest of the day after your scan, flush the toilet twice after each use.

Follow any instructions you receive from your healthcare team.

Ask your healthcare team when you can expect to learn the results of your PSMA PET scan. The healthcare professionals who do the PSMA PET scan can't tell you the results. You likely will get the results from the healthcare professional who ordered the test.

A radiologist looks at the PSMA PET scan images to determine the results. A radiologist is a doctor who specializes in using imaging tests to diagnose diseases. The radiologist looks at the images to find the places where the tracer builds up. These places might look brighter or more intense than the areas around them.

You might see a report with the PSMA PET scan results in your health record. It may help to keep in mind that the report is written for healthcare professionals, so the content may not be clear to others. Your healthcare professional or another healthcare team member will likely contact you to explain the results. The report often includes:

• Information about the tracer. The report may describe the tracer used for the test, including how it was prepared and how it was given. It also might include the brand name. Examples of brand names for PSMA PET tracers include Gozellix, Pylarify and others.
• Information about the imaging tests. A PSMA PET is often combined with CT or MRI. The report may include descriptions of which tests were used and how much of the body was scanned.
• Parts of the body where the tracer builds up. The radiologist may describe the images that the test made. The report might note each part of the body where the tracer builds up and whether the tracer in each part is expected or not expected. The results might describe each of these areas as having a low, intermediate or high amount of tracer.
• Diagnosis. The report often includes a summary of the results and the radiologist's diagnosis, which is sometimes called the impression. The radiologist may suggest other tests if more information is needed.

It's typical for the tracer to build up in certain healthy tissues. It's common for PSMA PET scan images to show a buildup of tracer around the eyes and in the salivary glands around the face. Also, the tracer often builds up in the liver, gallbladder, spleen, small intestine, colon and kidneys.

If the tracer builds up in a place where it isn't expected, it could be a sign of prostate cancer. Sometimes other tests and procedures are needed to be sure if it's cancer or not cancer. This might involve other imaging tests or a procedure to remove some cells for testing, called a biopsy.