What is PET, PET-CT and PET-PSMA?

PET (positron emission tomography) assesses the metabolism of the structures analysed such as bones, muscles, organs and tumours. It shows changes in cell metabolism that may or may not indicate the presence of a tumour. The test involves injecting a substance that shows up in certain cells (tumour cells in oncology, but they can be of a different type depending on the purpose of the test and substance used). This compound is connected to a radiation-emitting “radionuclide.” This radiation is detected by PET and indicates where these specific cells are located.

In the PET-CT (positron emission tomography – computed tomography) test, additional information is obtained by using PET and a CT scan simultaneously. In other words, the devices are synchronised, combining metabolic and anatomical imagery.

This test is used in cases where there is a suspicion of prostate cancer and is important in ascertaining the stage of the tumour and useful in assessing and planning treatment. It shows whether the tumour has spread to other parts of the body (if it has metastasised). It is increasingly used if a suspicion exists that the tumour has grown or recurred.

The use of a new tumour marker, called PSMA (prostate-specific membrane antigen), has made this test even more sensitive and precise and therefore increasingly common in prostate oncology.

Importance of the PET Test for Prostate Pathologies

These tests accurately identify areas where cancerous cells exist (whether in the prostate or other parts of the body) by identifying changes that occur in their cell metabolism.

The tests are relatively new and can be very useful in detecting whether a tumour exists in another place and in analysing whether cancer has recurred after treatment or if a tumour exists outside the prostate at the time of the diagnosis.

What is the PET Test Procedure?

It is non-invasive and very safe.

The test takes around 2 hours. A radiopharmaceutical is injected into the patient intravenously and it is necessary to wait for the substance, which emits low doses of radiation, to be detected in certain places in the body.

The most commonly used radiopharmaceutical is 18F-fluorodeoxyglucose (18F-FDG) which is associated with a radionuclide that emits a particular type of radiation. In the case of PET-PSMA, the most commonly used product is Gallium-68 PSMA


PET-PSMA is an alternative that has been used for several years and allows better definition of the stage and recurrence of the prostate cancer.

PET-PSMA uses a radioactive component associated with PSMA. PSMA is a glycoprotein located on the “surface” of prostatic cells and highly regulated in prostate cancer.

Therefore, it is possible to detect small tumours in their initial stages before they spread. This may not be possible with traditional PET.


Risks Associated with PET

There are few risks associated with PET, as it is a safe test despite using radiopharmaceuticals that emit radiation. However, the radiation level is very low.

These radiopharmaceuticals do not have side effects but may cause a little discomfort or reddishness at the point of injection.

Pregnant or breastfeeding women must inform their doctor before the test.

Dr. José Santos Dias

Clinical Director of the Instituto da Próstata

  • Bacherlor's Degree from the Faculty of Medicine at the University of Lisbon
  • Specialist in Urology
  • Fellow of the European Board of Urology
  • Autor dos livros "Tudo o que sempre quis saber Sobre Próstata", "Urologia fundamental na Prática Clínica", "Urologia em 10 minutos","Casos Clínicos de Urologia" e "Protocolos de Urgência em Urologia"

FAQs about PET

Is the PET Test important for treating prostate cancer?

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Does the patient need to prepare before the PET Test?

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When do you do a PET-CT Test with PSMA?

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What is PSMA?

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