A PET (Positron Emission Tomography) scan is a nuclear medicine examination that identifies disease activity in the body by tracking emissions from a small amount of liquid radiotracer following its injection into the blood stream.
The majority of PET scans use a type of radioactive sugar (FDG) to localise the cancer, as most cancers grow rapidly and have high sugar demand for that purpose. The cancers show up as “hot” on the PET scan, providing extra and at times more sensitive information regarding location and spread of disease in comparison to a conventional CT scan.
Unlike other cancers, prostate cancer commonly grows slowly and generally doesn’t appear “hot” on standard PET scans. PSMA PET differs from a standard PET scan in that it utilises a specially designed radiotracer aimed at targeting a protein present on most prostate cancer cells known as Prostate Specific Membrane Antigen (PSMA). As a result, tiny foci of prostate cancer can be detected.
This helps in tailoring treatment to the individual patient's needs and is particularly useful in the initial staging for men with ‘high risk’ prostate cancer and for men with elevated PSA after their initial prostatectomy or radiotherapy.
The example PSMA case above demonstrates the primary prostate cancer in the left image in the centre of the cross-hairs, bright orange ("hot") in the bottom left panel, while the image at right shows a small deposit of tumour in a pelvic lymph node, again in the centre of the cross-hairs. The tumour and its spread are otherwise very difficult to see without the benefit of the PSMA scan.