A positron-emission tomography (PET) scan is a relatively new way for doctors to assess if and where cancer has spread in your body.
While PET scans have been used for other cancers for many years, only recently has PET scan gained traction for patients with prostate cancer. A PET scan helps to visualize metabolic or biochemical function of your tissues and organs and typically captures images of your body from the top of the head to mid-thigh. This type of scan uses a radioactive drug (a tracer) to show normal and abnormal activity inside the body, often detecting signs of prostate cancer before they can be seen on other imaging tests, such as CT scan or magnetic resonance imaging (MRI). PET images are often combined with CT (called PET CT scans) or MRI (call PET MRI scans).
Traditional PET scans (which are still commonly used for other cancers) rely on the cancer cells burning glucose sugars to allow for imaging of the tumor cells. However, this is not reliable in prostate cancer. Thus, we rely on alternative approaches. There are two FDA approved PET CT scans that are commonly used in men with prostate cancer: fluciclovine F-18 PET CT (also called a Axumin PET CT scan) and prostate-specific membrane antigen (PSMA) PET CT. There are other approaches (including choline-PET/CT) that are used in some centers but are not widely available.
Axumin PET CT Scan
Since prostate cancer cells absorb amino acids (the building blocks of proteins) much faster than normal cells, Axumin takes advantage of this mechanism by linking a radioactive tracer to an amino acid. Because of the quicker uptake of amino acids (and the amino acid linked radiotracer) the radiation concentrates inside the prostate cancer cells, allowing the radiation signal to localize prostate cancer cells, wherever they may be in the body. The Axumin PET CT scan is FDA approved for men who have developed a rising PSA after previous radiation or surgery for their prostate cancer.
PSMA PET CT Scan
PSMA is a protein that lives in the walls of prostate cancer cells. While there are a number of ways to target PSMA for imaging purposes, the two most common PSMA PET CT scans used in the United States are Gallium (Ga) 68 PSMA-11 PET CT and piflufolastat fluorine (F) 18-PSMA PET CT (also called a Pylarify PSMA PET CT scan). Pylarify is a radiotracer consisting of the PSMA-targeting agent DCFPyL, and labeled with the positron-emitting isotope F 18.
In addition to being FDA approved for men who have developed a rising PSA after previous radiation or surgery (as Axumin is), both Ga 68 PSMA-11 and Pylarify PSMA PET CT scans are approved for patients newly diagnosed with prostate cancer who are at high risk of cancer spread (ie. metastasis) before treatment with surgery or radiation (ie. staging of high-risk presumed localized disease). Studies have shown that for both of these types of PSMA PET CT scans, with increasing PSA values there is increasing ability and accuracy to detect prostate cancer cells that are outside of the prostate, most commonly in the lymph nodes and bones.
When undergoing a PET scan, the radiotracer is most commonly injected into a vein in your hand or arm. It is important to stay well hydrated prior to injection of the radiotracer and you should continue drinking and urinating for the first few hours following the PET CT scan, in order to reduce radiation exposure. Immediately prior to undergoing the study, you will be asked to urinate and during imaging you will be positioned on your back with arms above your head.
Although the radiation dose is low for a PET CT scan, it is not advised for an infant or pregnant woman to accompany you (to and from the imaging center) and it is generally advised that you should avoid close contact with them for 12 hours following a PET CT scan. The majority of men will not have any side effects or adverse reactions from the radioactive tracer used during a PET CT scan, although infrequently some men may have a headache, abnormal taste, and fatigue for a day or two.
Historically, men with prostate cancer that is suspected to have spread outside of the prostate gland, or among those who are suspected of having disease recurrence after surgery or radiation, were imaged with a CT scan and bone scan. However, these tests often miss small amounts of disease. Because of new technological capabilities, PSMA PET CT imaging is the most common “next generation imaging” modality in these situations, with the goal of more accurately finding if and where the prostate cancer has spread, and allowing better treatment selection as a result.