PSMA PET Scan: Your Questions Answered

A PSMA PET scan is an advanced imaging technique that plays a crucial role in managing prostate cancer. It utilizes a radioactive tracer that specifically targets prostate-specific membrane antigen (PSMA), a protein commonly found on prostate cancer cells. This allows for precise detection and localization of cancer throughout the body, including areas that might be missed by older imaging methods. By providing detailed insights into the spread or recurrence of prostate cancer, PSMA PET scans significantly aid healthcare providers in planning effective treatments and monitoring patient response.

How Does PSMA PET Scan Work?

A PSMA PET scan operates by leveraging the presence of a specific protein called prostate-specific membrane antigen (PSMA) that is found on the surface of prostate cancer cells. When a patient undergoes the scan, a small, safe amount of a radioactive tracer, such as Gallium-68 PSMA-11 or piflufolastat F-18, is injected into a vein, typically in the arm. This tracer is designed to bind specifically to the PSMA proteins on the cancer cells.

After the injection, there’s a waiting period, usually around an hour or so, to allow the tracer to circulate throughout the body and accumulate in any areas where prostate cancer cells are present. During this time, the patient rests quietly. Once the tracer has had sufficient time to disperse, the patient is asked to empty their bladder before proceeding to the scanner.

The patient then lies on a cushioned table that slides into a large, doughnut-shaped or short tunnel-like machine. This machine is the PET scanner, which detects the small amounts of radiation emitted by the concentrated tracer wherever it has bound to PSMA-positive cancer cells. The scanner is often combined with a CT scan or sometimes an MRI scan, which provides detailed anatomical images of bones and organs. This combination allows for a clearer picture of exactly where the tracer has accumulated within the body.

The PET scan itself typically takes about 20 to 60 minutes, during which it is important for the patient to remain very still to ensure clear images. The scanner produces buzzing and clicking sounds while it works. After the scan, a technologist reviews the images to confirm they are clear, and then a radiologist, who specializes in interpreting these images, examines them to identify any areas where the tracer has built up, which could indicate the presence of prostate cancer. These areas will appear brighter or more intense on the scan. The entire procedure, from injection to image review, generally takes around two to two and a half hours.

What To Do Before Your PSMA PET Scan?

• Review Medical History and Discuss Concerns: A healthcare provider will typically review your medical history and perform a physical examination. If you have any fears, such as a fear of needles (trypanophobia) or enclosed spaces (claustrophobia), it’s important to let your provider know. They can offer coping strategies or suggest a mild sedative to help you be comfortable during the scan.
• Hydration: It is generally recommended to stay well hydrated both the day before and on the day of the scan. You might be advised to drink around 1 liter of fluids before arriving for your appointment.
• Medications: You can generally take your necessary medications as usual with water, unless specifically instructed otherwise by your healthcare provider. There’s usually no need to stop or delay your regular medications.
• Food and Drink: Unlike some other PET scans, there are no special instructions regarding fasting for a PSMA PET scan. You can usually eat and drink normally before the scan.
• Clothing and Accessories: Wear comfortable clothing, ideally without any metal zips or buttons. It’s best to leave jewelry, eyeglasses, and any other metal accessories at home, as you will be asked to remove all metal objects before the scan. If your clothing contains metal, you may be asked to change into a gown.
• Bringing Prior Imaging: If you have had previous scans elsewhere, bring all relevant imaging with you on the day of your scan so it can be uploaded onto the system for comparison.
• Inform Staff if Applicable: Notify the staff at the time of booking if you:
  • Have kidney failure
  • Have diabetes
  • Have previously had a reaction to intravenous contrast for CT scans
  • Are severely claustrophobic
  • Have any allergies
  • Are pregnant or breastfeeding (this may require special considerations or a different approach).
• Accurate Medical History: Providing accurate dates of your most recent medical history, including prior imaging, surgery, radiotherapy, and chemotherapy, will be helpful during the booking process.
• Arrival Time: Be sure to arrive on time for your appointment. The radioactive tracer has a very short shelf life, so being late might mean the scan cannot proceed. You will be given an arrival time well in advance of your camera time.
• Companions: If you need to bring someone with you, note that they might be asked to wait in the lobby during the scan. It’s generally advised not to bring children

PSMA PET-Scan vs Other Imaging

• PSMA PET Scans:
  • Directly target prostate cancer cells on a molecular level by binding to PSMA protein.
  • Offer more accurate and earlier detection of prostate cancer.
  • Excel at finding very small tumors, even those missed by conventional imaging.
  • More effective and precise in localizing metastatic prostate cancer throughout the body.
  • Can detect significantly more prostate lesions than older PET techniques like fluciclovine PET, especially in recurrent cases.
  • Often combined with CT or MRI for detailed functional and anatomical information.
• Other Imaging (CT, MRI, Bone Scans, Older PET):
  • Rely on visualizing anatomical structures or general metabolic activity.
  • Can miss very small tumors or subtle lesions.
  • May have challenges in distinguishing cancer from other conditions, potentially leading to false positives (e.g., bone scans).
  • Less precise in pinpointing individual prostate cancer cells or microscopic spread.

Read OncoDaily’s Special Article About PET Scan

Adverse Effects

While PSMA PET scans are generally considered safe, some individuals may experience temporary side effects. The amount of radiation exposure during the scan is small, comparable to a standard CT scan, and is generally regarded as safe, with the diagnostic benefits typically outweighing any potential risks. The radioactive tracer itself is eliminated from the body within a few days.

Common, usually mild, side effects can include a feeling of fatigue, headaches, or a temporary alteration in taste (dysgeusia). Patients might also experience minor soreness or a slight pinch at the site where the radioactive tracer is injected into the vein. In rare instances, a mild allergic reaction, such as hives or itching, may occur.

It’s also worth noting that the tracer naturally accumulates in certain healthy tissues, such as around the eyes, in salivary glands, the liver, gallbladder, spleen, small intestine, colon, and kidneys. This normal uptake can sometimes make it challenging to detect prostate cancer cells that may have spread to these areas, potentially leading to a “false negative” result if cancer is present but not clearly visible. Conversely, in rare cases, other types of cancer or benign conditions can also show low levels of PSMA uptake, which might result in a “false positive,” requiring further testing to confirm a prostate cancer diagnosis.

After the scan, if you’ve received any mild sedative for comfort, you will need someone to drive you home. Additionally, as a precautionary measure due to the residual radioactivity, it’s recommended to avoid close contact with young children and pregnant women for about 12 hours following the injection. If you plan to fly within 24 hours, it’s advisable to obtain a note from your healthcare team to show airport security, as the tracer might trigger radiation detectors. Any swelling at the injection site should be reported to your healthcare provider.

Written By Aren Karapetyan, MD