PSMA Test: Types, Uses, and Procedure

A PSMA Test is an advanced nuclear medicine diagnostic technique that has proven useful in assessing prostate cancer. A PSMA PET scan uses trace amounts of a radioactive tracer compound to target prostate-specific membrane antigen (PSMA), which is up-regulated on many prostate cancer cells. In combination with CT, the scan can help doctors determine the location and extent of prostate cancer tumours. At Molecular Diagnostics and Therapy, advanced nuclear medicine and PET-CT diagnostics help assess and monitor prostate cancer, as directed by your treating doctor.

What Is a PSMA Test?

PSMA stands for Prostate-Specific Membrane Antigen. It is a protein on the surface of prostate cancer cells and can be up-regulated significantly in comparison to normal prostate cells. A PSMA PET scan involves injecting a PSMA-targeting radiotracer through an intravenous (IV) line. The radiotracer then binds to cells that carry PSMA, enabling the PET scan to detect where the cancerous cells are.

When used in combination with a CT scan, the nuclear medicine PET (Positron Emission Tomography) image identifies regions where the radiotracer has accumulated, while the CT (Computed Tomography) image enables the radiologists to identify the specific anatomical location and surrounding structures. Together, both scans provide complementary information and give doctors a better understanding of where suspected cancerous tumours might be.

Types of PSMA PET Scans

A variety of PSMA radiotracers may be used depending on availability, clinical need, and other factors. Gallium-68 PSMA and Fluorine-18 PSMA are examples of radiotracers that are occasionally used. While these radiotracers may have differences in radioactive isotope (radioactive element), they are generally PSMA-targeted and are selected by the nuclear medicine team based on the clinical indication and available equipment.

What Is a PSMA PET-CT Scan Used For?

A PSMA PET-CT scan may be recommended in different situations involving prostate cancer.

Initial Staging

In some men presenting with newly diagnosed prostate cancer, a PSMA PET-CT scan may help determine whether prostate cancer has spread beyond the prostate gland. This is an important consideration when determining the staging of prostate cancer and, therefore, which treatment options are appropriate.

Detecting Recurrent Prostate Cancer

PSMA PET-CT scanning may also be used to help detect prostate cancer that recurs (returns or progresses) after initial treatment for prostate cancer, particularly when the PSA (Prostate-Specific Antigen) level rises after surgery or radiotherapy for prostate cancer. In such cases, the scan may help identify regions of recurrent prostate cancer that would not typically be apparent with conventional imaging.

Assessing Spread of Disease

PSMA PET-CT scanning can provide information about the spread (metastases) of prostate cancer, including involvement of lymph nodes (common sites of prostate cancer metastasis) and bones (another common site of prostate cancer metastasis). Knowing whether cancer has spread may also help determine the relative appropriateness of different treatment options.

Before PSMA-Targeted Therapy

PSMA imaging may also be used to help determine whether a man is considered appropriate for PSMA-targeted radioligand therapy. The PSMA PET scan helps determine whether the cancerous lesions express enough PSMA for the radioligand to bind effectively for the proposed treatment.

PSMA PET Scan Procedure

The procedure is generally simple but has several steps. A patient is first asked to present relevant medical documents and information about their prostate cancer diagnosis, any prior treatments for prostate cancer, PSA (prostate-specific antigen) results, and any prior imaging. A cannula is then placed by a healthcare professional, and a small amount of the selected PSMA radiotracer is injected.

The patient is then instructed to wait for a certain period while the tracer accumulates in the body's tissues. For many PSMA PET scans, this waiting period is about an hour long but may be extended depending on the facility and the radiotracer used. The patient is then positioned on the scanning table, which moves through a PET-CT scanner to acquire PET and CT images. This scanning procedure generally takes about 30 minutes, although because of the initial waiting period and preparation, this is only a small part of the overall examination.

How Should You Prepare for a PSMA PET Scan?

The preparation steps for a PSMA PET scan may vary depending on the radiotracer and facility. In general, for most PSMA PET-CT scans, fasting is not required, and patients are encouraged to take their regular medication as per their physician's instructions, unless otherwise informed. Patients are encouraged to stay well-hydrated and may even be instructed to empty their urinary bladder at certain points during the procedure, as some PSMA PET radiotracers are excreted in the urine. Always follow the specific instructions provided by the nuclear medicine centre performing the PSMA PET scan.

Is a PSMA PET Scan Safe?

A PSMA PET-CT scan makes use of trace amounts of a radiotracer, which is selected and administered according to nuclear medicine protocols. Like most other imaging procedures, a PSMA PET-CT scan is not foolproof. Regions of tracer uptake are not always cancerous, and very small cancerous lesions may occasionally be missed. Moreover, healthy organs typically have some tracer uptake, and so the findings must always be interpreted in conjunction with one's PSA level, biopsies (if any), treatment history (if any), and other relevant health information.

What Happens After the Scan?

The scanned images are then reviewed and reported upon by a nuclear medicine physician or imaging specialist. The report will generally highlight any regions of increased tracer uptake. The patient's doctor will then review the report as part of their wider clinical assessment of the patient. Where the scan results are inconclusive, additional imaging, lab tests, or biopsies (if applicable) may sometimes be recommended.

Why Choose Molecular Diagnostics and Therapy?

Molecular Diagnostics and Therapy provides advanced nuclear medicine and PET-CT diagnostics for patients who require expert imaging. PSMA PET-CT scanning provides invaluable information about prostate cancer localisation and spread where it is appropriate. The most appropriate type of imaging depends on one's diagnosis, PSA level, treatment history, symptoms, and overall clinical presentation. 

Conclusion

A PSMA PET scan is an advanced nuclear medicine imaging procedure that targets PSMA to provide invaluable information about prostate cancer lesions. A PSMA PET-CT scan combines nuclear medicine and precise anatomical imaging to help determine the localisation and extent of prostate cancer tumours. This scan may be used for initial staging, detecting prostate cancer recurrence, determining the spread of prostate cancer, and determining the suitability for PSMA-targeted treatment. However, a PSMA PET-CT scan is not interpreted in isolation. The scan results must always be interpreted in conjunction with one's overall medical presentation. Molecular Diagnostics and Therapy provides advanced diagnostic imaging for the assessment and management of prostate cancer.