PSMA PET scan: what it is, how it works and what to expect

The NHS describes a PET scan as a test that uses a small amount of radiation to scan inside your body and is used to diagnose and plan treatment for conditions such as cancer. A PET scan can be combined with a CT scan (PET-CT) if doctors need more detailed images.

In a PSMA PET-CT scan, the tracer is designed to attach to prostate-specific membrane antigen (PSMA). The Royal Marsden leaflet explains that the tracer binds to a form of protein present in all prostatic tissue and that abnormal prostate cells absorb far more of the tracer and so show up on the scan. The Oxford leaflet says PSMA is a type of protein that prostate cancer cells have more of, and that the scan may be able to detect prostate cancer and any spread earlier than other scans, which could benefit your treatment.

NHS England's clinical panel report describes PSMA PET-CT radiotracers for patients with high-risk primary prostate cancer or biochemical recurrence, meaning a rising PSA after treatment. It says that in 2019, owing to a breakdown in the choline supply chain, an interim commissioning position allowed reimbursement of two alternative radiotracers, gallium-68 PSMA and fluorine-18 PSMA, and that the policy proposition would supersede it. The panel recommended the proposition proceed as a routine commissioning proposition.

The panel summarised studies finding significant differences with 68Ga-PSMA-11 PET-CT compared with conventional imaging in the accuracy of imaging, equivocal findings, change in patient management and radiation exposure for high-risk disease, with higher detection rates in recurrent disease. Who qualifies, and from where, is decided by the specialist team under NHS England criteria, so this page cannot say whether the scan applies to a particular person.

NICE also notes that PSMA positivity matters for some treatments: its guidance on lutetium-177 vipivotide tetraxetan (Pluvicto) concerns PSMA-positive hormone-relapsed metastatic prostate cancer, and says it is not normally available on the NHS for that indication, so your doctor should talk with you about other options.

Instructions vary by hospital, so follow the leaflet you are given. The Royal Marsden says no special preparation is required for the scan. Oxford says you may eat as normal and take any medication as usual, and encourages staying hydrated before and after the scan as this helps flush the tracer through the body. It asks you to wear warm, loose, comfortable and metal-free clothing, including no jewellery, zips and bra hooks.

The Oxford leaflet asks you to contact the department beforehand if you are pregnant, breastfeeding, in contact with children, have mobility needs, weigh over 100 kg, have allergies or incontinence, or have another appointment that day, and to bring only one accompanying adult and no children. By comparison, the general NHS PET scan page says that for many PET scans you may be asked to stop eating 6 hours before, so check the instructions for your own scan.

A radioactive tracer is injected into a vein, usually in the arm, similar to a blood test. Royal Marsden says you rest in a preparation room for about an hour, Oxford says 1 and a half hours seated or reclined, while the tracer is absorbed. You then lie on a bed that moves through an open ring-shaped scanner. Royal Marsden gives the scan time as approximately 20 to 45 minutes and Oxford 30 to 40 minutes, and you breathe normally with no instructions to follow. Depending on the scan you may have your arms above your head or by your sides.

Oxford says there are no known side effects from the radioactive injection, and Royal Marsden says the tracer will not produce side effects and will not prevent you driving. Staff may offer numbing spray for the injection if you are afraid of needles.

The NHS says the radiation from a PET scan tracer drops to a safe level quickly and any radiation can very slightly increase the risk of cancer in the future, which doctors weigh against the benefit. The Royal Marsden gives the risk associated with the exam as less than 0.1%, and Oxford describes the dose as the equivalent of about 5 years of natural background radiation, with minimal risk.

Afterwards you can leave immediately and eat and drink as normal. Royal Marsden asks you to avoid prolonged close contact with pregnant people and young children for the rest of the day, and Oxford specifies no close contact with pregnant women or any children for 6 hours, with plenty of fluids to flush the tracer. Follow your own hospital's instructions.

Royal Marsden says the scan is reported by the nuclear medicine consultant within 24 hours and the result made available to the doctor who referred you; the general NHS PET page says results usually take 1 or 2 weeks and a follow-up appointment may be needed. If you have not heard anything after a few weeks, contact the doctor who referred you.

The result informs, but does not replace, other information such as PSA, MRI and biopsy findings and your general health. Ask your urology or oncology team how the result would change the plan, and whether the scan is available through the NHS for your situation. NHS access is determined by commissioning criteria, and some people have a PSMA PET scan privately, in which case the same report should be shared with the NHS team.