What Is a PSMA PET Scan?
A PSMA PET scan, or prostate-specific membrane antigen positron emission tomography scan, is a recently developed imaging test used for people with prostate cancer. It looks for a protein called prostate-specific membrane antigen, which is produced by most, but not all, prostate cancers.
The test can spot signs that the disease has metastasized, meaning it has spread beyond the prostate to other parts of the body. When this process begins, the cancer is often small and difficult to detect. PSMA PET scans are better than other imaging tests at spotting metastasis early. It’s used in three different scenarios:
- To be sure that your cancer has not yet metastasized. In such cases, the disease may still be treatable with radiation or surgery. Once prostate cancer has spread, other treatments are required.
- To check for signs of metastasis in people who have already undergone surgery or radiation but whose prostate-specific antigen (PSA) tests indicate their cancer may have returned.
- To find out whether you’re a candidate for a prostate cancer treatment called lutetium Lu-177 vipivotide tetraxetan (Lu-177 PSMA), which targets prostate cancer that involves PSMA. A small number of prostate cancers do not produce this protein.
How Does a PSMA PET Scan Work?
A PET scan uses what’s called a radiotracer, or simply a tracer, which is a small amount of radioactive material. It is injected into your bloodstream and collected in areas of concern. During the scan, the radiotracer lights up wherever it collects. This allows your doctor to pinpoint abnormalities.
In PSMA PET scans, these radiotracers are combined with a chemical that attaches itself to PSMA proteins, which can be found on the surface of prostate cancer cells in most people with the disease. If your cancer has spread beyond your prostate, the areas where it can be found will be identified during the scan. The most common places where metastatic prostate cancer is found include:
- Bones
- Liver
- Lungs
- Lymph nodes
The FDA has approved three radiotracers for use in PSMA PET scans:
- Flotufolastat F 18 injection (Posluma)
- Gallium 68 PSMA-11
- Piflufolastat F 18 injection (Pylarify)
Your PSMA PET scan will be done alongside a CT scan or an MRI test. These two imaging tests will provide your doctor with more detailed pictures of what’s going on.
Who Might Need a PSMA PET Scan?
Your doctor may recommend this scan if you:
- Are at higher risk for prostate cancer that may spread. This may depend on your biopsy results and some other things.
- Have a high PSA after prostate cancer surgery or radiation therapy. A high PSA may be a sign of cancer, but it can also be a sign of noncancer things.
- Have a few small metastasized tumors (your doctor will call them oligometastases) when you’re diagnosed.
PSMA PET Scan Procedure
Once you get to the test site, you’ll change into a hospital gown and then receive an injection that contains the radiotracer. It takes about an hour for the radiotracer to move throughout your body.
After that hour has passed, you’ll lie on a table and be moved inside the PET scanner, a large machine with a donut-shaped hole large enough to fit patients. Your scan will last 20-30 minutes, but expect about two hours for the entire process. You can leave once the scan is done. Though unlikely, you may experience temporary side effects, including a headache, fatigue, or a change in taste.
How to prepare for your PSMA PET scan
There are several things you must do before your scan. Your doctor will give you specific instructions, but expect the following:
- If you are claustrophobic or anxious, discuss this with your doctor when scheduling your scan. You may be prescribed an antianxiety medication to take before your scan.
- Eat a low-carb diet for 12-24 hours before your scan. This means no pasta, bread, cereal, or foods with high amounts of carbohydrates. Meat, hard cheese, eggs, tofu, and non-starchy vegetables are fine.
- Stop eating six hours before your scan.
- Drink 32 to 64 ounces of water in the two hours before your exam.
- Take your prescribed medications as usual, unless your doctor tells you not to. If you have diabetes, take your diabetes medications at least four hours before your scan. You will not be able to use a continuous glucose monitor during your scan.
PSMA PET vs. Other Imaging Scans
PSMA PET scans outperform other types of imaging scans. They can precisely pinpoint the location of very small amounts of cancer anywhere in your body. That allows your doctor to identify trouble spots very early. CT scans, MRI scans, and bone scans can’t locate cancer with the same level of precision.
Also, PSMA PET scans are very specific compared with other imaging tests. That’s because they attach only to cells with PSMA proteins. This allows doctors to more confidently identify prostate cancer. Bone scans, on the other hand, may also reveal damage not caused by cancer, such as arthritis. That could lead to a false positive — meaning the test reveals what appears to be cancer but is not — and require additional testing to confirm those results. Some types of MRI, according to recent research, miss 1 in 6 prostate cancer tumors. This is called a false negative, in which the test fails to find cancer that’s actually there.
Researchers have found that PSMA PET scans correctly detect metastatic prostate cancer in more than 9 out of 10 cases. Standard imaging, which combines CT and bone scans, has a success rate of only 65% for finding metastatic prostate cancer.
If you've had your prostate removed (a procedure called radical prostatectomy), PSMA PET scans are more effective than the standard type of PET scan at finding cancer when it recurs.
Other Advantages of a PSMA PET Scan
In addition to outperforming other imaging tests to detect metastatic prostate cancer, the PSMA PET scan offers the following benefits:
It may help guide treatment. PSMA PET scans can locate very small pockets of cancer cells. That allows your doctor to plan treatment that targets those areas very precisely. For example, radiation treatments can target just those areas rather than exposing larger parts of your body to radiation. PSMA PET scans can also help guide surgical treatment of prostate cancer.
You’re exposed to less radiation. PSMA PET scans expose you to lower levels of radioactive material compared with other imaging tests that also require radioactive tracers, such as standard CT scans.
Concerns About PSMA PET Scans
There are also some things that you might want to keep in mind as you consider whether or not to get a PSMA PET scan. For example:
They cost much more than CT and bone scans. Doctors hope that as more people get these scans, the price will come down.
There is some radiation. Depending on how much radiation you've had before, this might raise your chance of more cancer.
They can also produce false positives. PSMA PET scans track down PSMA proteins, found on the surface of most prostate cancer cells. However, these proteins sometimes pop up in other cancers, such as rectal cancer and lung cancer. Infections, as well as some diseases unrelated to cancer (such as the bone disorder Paget’s disease), can also release the PSMA protein, which will show up on a PSMA PET scan. However, the scans accurately identify prostate cancer about 90% of the time.
Be sure to talk with your doctor about whether a PSMA PET scan is a good idea for you.
How Much Does a PSMA PET Scan Cost?
Recent research puts the average cost of a PSMA PET scan at $5,438. Conventional imaging costs an average of $2,161. Keep in mind that both Medicare and most commercial health insurance plans cover PSMA PET scans.
Takeaways
PSMA PET scans are the most accurate imaging test for finding prostate cancer that has spread to other parts of your body. This test can also find it early and help guide your treatment. These scans are not perfect. Though they correctly identify prostate cancer about 90% of the time, false positives can occur, meaning they can mistake something else for prostate cancer. Also, a small number of people with prostate cancer don't have a cancer that produces the PSMA protein, so they wouldn't benefit from this scan.
PSMA PET Scan FAQs
Can a PSMA PET scan detect other cancers?
The PSMA PET scan can detect the PSMA protein in some other cancers, such as lung cancer, colorectal cancer, kidney cancer, thyroid cancer, and breast cancer. However, it’s currently only approved for use with prostate cancer. In some cases, finding PSMA in other cancers leads to false positives for prostate cancer. As researchers study this imaging test more, it may prove useful for detecting cancers other than prostate cancer.
At what PSA level should a PSMA scan be done?
PSMA PET scans are typically done for two reasons:
- You may have an aggressive form of prostate cancer likely to spread (metastasize). One factor that indicates your cancer is aggressive is a PSA of 20 nanograms per milliliter (ng/mL) or higher. If that’s the case for you, your doctor likely will recommend a PSMA PET scan.
- You have been treated for prostate cancer, but it shows signs of coming back. If you have had a radical prostatectomy, in which your prostate and some surrounding tissue are removed, your PSA level should be very low — below 0.1 ng/mL — if not undetectable entirely. If follow-up tests show a PSA of 0.2 or higher, that likely means your cancer has returned. PSMA PET scans can detect cancer at PSA levels as low as 0.2 ng/mL, though they become more accurate at higher levels.
How long does a PSMA PET scan take?
The scan itself takes 20-30 minutes, though you should expect about two hours from the time you arrive for your scan.
Where is the PSMA PET scan available?
A growing number of medical centers offer PSMA PET scans. Your doctor can tell you where to find the most convenient place to schedule yours.
