PSMA Scanning

A PSMA scan - more fully a PSMA PET/CT - is a specialised imaging test that shows where prostate cancer cells are in the body. It has become one of the most important tools for accurately staging prostate cancer and for finding cancer that has come back after treatment.

What is PSMA?

PSMA stands for prostate-specific membrane antigen, a protein found in large amounts on the surface of most prostate cancer cells. For a PSMA scan, a small amount of a radioactive tracer that is designed to attach to PSMA is injected into a vein. The tracer travels through the body and binds to prostate cancer cells wherever they are.¹

The scan combines two techniques in a single session: PET (positron emission tomography), which detects the radioactive tracer and lights up areas where prostate cancer cells have gathered, and CT (computed tomography), which provides the detailed anatomical picture that shows exactly where those areas are. Together they produce a whole-body map of any PSMA-avid disease.

Why is a PSMA scan used?

PSMA PET/CT is used mainly in two situations:

• Staging newly diagnosed prostate cancer - in men with higher-risk cancer, a PSMA scan helps determine whether the cancer is confined to the prostate or has spread to lymph nodes or bones. This information is important for planning treatment.²
• Investigating a rising PSA after treatment - if the PSA level rises after surgery or radiotherapy (biochemical recurrence), a PSMA scan can often locate where the cancer has returned, even at low PSA levels where older scans would show nothing.³

How does it compare with conventional scans?

Traditionally, prostate cancer was staged with a CT scan and a bone scan. A large Australian randomised study (the proPSMA trial) compared PSMA PET/CT with this conventional imaging in men with high-risk prostate cancer before treatment. It found that PSMA PET/CT was significantly more accurate at detecting the spread of cancer, and that it changed management decisions more often than conventional imaging did.²

Because of results like these, PSMA PET/CT is now recommended in major international guidelines as an option for staging higher-risk prostate cancer, and it is increasingly used in place of - or in addition to - CT and bone scans.⁴

What does the scan involve?

The exact process varies between imaging centres, but a PSMA PET/CT usually involves:

• A small injection of the PSMA tracer into a vein in the arm.
• A waiting period, typically around 45 to 60 minutes, while the tracer circulates and binds to any prostate cancer cells.
• The scan itself, during which you lie still on a bed that passes slowly through the scanner. This part usually takes around 20 to 30 minutes.

The scan is painless. The amount of radiation involved is comparable to that of other nuclear medicine scans, and the tracer clears from the body over the hours that follow. Your imaging centre will give you specific preparation instructions before the appointment.

Understanding the results

Areas where the tracer has concentrated show up as bright spots on the scan and usually indicate prostate cancer cells. However, PSMA is not completely specific to prostate cancer - some normal tissues (such as the kidneys, salivary glands and liver) naturally take up the tracer, and occasionally other conditions can also show uptake. For this reason, the images are always interpreted by a specialist nuclear medicine physician and considered alongside your PSA, biopsy results and other investigations.¹

Availability and cost

In Australia, a Medicare rebate is available for PSMA PET/CT in certain defined situations, including the staging of some higher-risk prostate cancers and the assessment of suspected recurrence. Whether a rebate applies in your case depends on the specific clinical circumstances, and there may still be an out-of-pocket cost. Your urologist and the imaging centre can advise you about eligibility and cost before the scan is booked.

Where a PSMA scan fits at Urology NSW

Whether a PSMA scan is appropriate depends on your individual situation - the grade and stage of the cancer, your PSA level, and where you are in the diagnosis or treatment pathway. It is one part of a broader assessment rather than a test that every man with prostate cancer needs. If you have questions about staging or about a rising PSA, a consultation with a urologist is the appropriate starting point.