You might have a PET scan to find out more about the stage of your cancer.
PET stands for positron emission tomography. This type of scan can show how body tissues are working, as well as what they look like.
You’ll usually have a PET scan in the x-ray (radiology) department as an outpatient. These scanners tend to be only in the major cancer hospitals. So you might have to travel to another hospital to have one.
A radiographer operates the scanner. It usually takes between 30 and 60 minutes.
Why you might have a PET scan
A PET scan can help to:
- diagnose cancer
- stage the cancer, so doctors know whether it has spread
- decide the best treatment for your cancer
- show how well a cancer treatment is working
After you have had treatment for cancer, a CT scan may show an area that looks like there might still be some cancer left. This might not be cancer but scar tissue left over from the cancer killed off by your treatment. A PET scan can sometimes show whether this tissue is active cancer or not.
Preparing for your PET scan
For most PET scans, you need to stop eating for about 4 to 6 hours beforehand. You can usually drink water during this time.
You might have instructions not to do any strenuous exercise for 24 hours before the scan.
Call the number on your appointment letter if not eating is a problem for you, for example if you’re diabetic. You might need to adapt your diet and sugar control, and your appointment time could change.
Some people feel claustrophobic when they‘re having a scan. Contact the department staff before your test if you’re likely to feel like this. They can take extra care to make sure you’re comfortable and that you understand what’s going on. Your doctor can arrange to give you medicine to help you relax, if needed.
Your radiographer might ask you to change into a hospital gown. You have to remove any jewellery and other metal objects such as hair clips. Metal interferes with the images produced by the scanner.
You have an injection of a dye called a radiotracer about an hour before the scan. You’ll have this injection through a small plastic tube called a cannula in your arm.
You need to rest and avoid moving too much during this hour. This allows the drug to spread through your body and travel to places where glucose is used for energy, like your brain.
When you arrive at the scan department
Your radiographer takes you into the scanning room. The PET machine is large and shaped like a doughnut.
You have most scans lying down on the machine couch on your back.
Once you’re in the right position, your radiographer leaves the room. They can see you on a TV screen or through a window from the control room. You can talk to each other through an intercom.
Having the PET scan
The couch slowly slides backwards and forwards through the scanner. The machine takes pictures as you move through it.
The scan is painless but can be uncomfortable because you have to stay still. Tell your radiographer if you’re getting stiff and need to move.
It’s not particularly noisy but you’ll hear a constant background noise.
When it’s over, your radiographer will come back into the room and lower the couch so you can get up.
Voiceover: PET and PET-CT scans help to diagnose and stage some cancers. They can also help your doctor decide which treatment you need and whether your treatment is working. PET and PET-CT scans show slightly different things but the process of having them is the same.
Radiographer: Ok so first of all I’d like you to get changed
Voiceover: For some scans you should not eat for 4 to 6 hours beforehand, for others there is no preparation. Your appointment card will give you details of what you need to do. One you have changed into your gown the radiographer will weigh and measure you. Then you have an injection of a very small amount of a radioactive drug called a tracer. This is what shows up on the scan. The drug is usually a form of glucose.
Radiographer: Right I am starting now, does that feel ok?
Girl: Yeah that’s fine
Radiographer: Is it comfortable?
Radiographer: Right, that’s all in now. I am going to take the needle away because we don’t need that any more
Voiceover: After the injection you rest for about an hour. This allows the tracer to spread through your body. The scan shows up cancer because they use glucose in a different way from normal tissue. When you are ready for the scan the radiographer helps you lie on the couch in the correct position.
Radiographer: I am just going to pop this under your knee just to help your back stay comfortable. You’re going to move in and out of the scanner nothing is going to touch you or anything like that you must keep very still. Close your eyes because this light is quite bright.
Voiceover: Once you are in position and comfortable the radiographer will leave the room. You need to lie as still as possible while you are having the scan. You won’t feel anything but it can be difficult to lie still for up to an hour. If you begin to feel unwell or want some help you will be able to get the radiographers attention.
Radiographer: Are you ok in there Charlotte?
Voiceover: The radiographer control the scan from a separate room but they will be able to hear and see you all the time you are having the scan and will check you are ok
Radiographer: We won’t be long now. Ok that’s all done now; we will get you out of there. Are you ok? Good. You can pop your arms down now
Voiceover: One the scan is finished you can go home. As a precaution you should avoid contact with pregnant women and small babies for six hours after your scan. Your specialist will give you the results usually within a couple of weeks
After your PET scan
Your radiographer removes the tube from your arm before you go home.
You can then eat and drink normally.
Someone will need to take you home if you’ve had medicine to help you relax. You won’t be able to drive for the rest of the day as you might be drowsy.
The radiotracer gives off very small levels of radiation that go away very quickly. But for the rest of the day you shouldn’t have close contact with pregnant women, babies or young children.
A PET scan is a safe test for most people. But like all medical tests it has some risks. Your doctor and radiographer make sure the benefits of having the test outweigh these risks.
Pregnant women should only have the scan in an emergency. There’s a risk that the radiation could harm the developing baby. Contact the department beforehand if you're or think you might be pregnant.
If you're breastfeeding, let the department know a few days before your appointment. They will let you know if you need to stop breastfeeding for a length of time after having the radioactive drug. You might need to store enough expressed milk for at least one feed.
Exposure to radiation from the radiotracer during a PET scan slightly increases your risk of developing cancer in the future. Talk to your doctor if this worries you.
Bruising and swelling
You might get a small bruise around the area where they put the needle in.
There's is a risk that the radioactive tracer will leak outside the vein. This can cause swelling and pain in your arm but it's rare.
Rarely, people have an allergic reaction to the radioactive tracer. This most often starts with weakness, sweating and difficulty breathing. Tell your radiographer immediately if you feel unwell.
Getting your results
You should get your results within 1 or 2 weeks at a follow up appointment.
Waiting for test results can be a worrying time. You can contact your specialist nurse if you’re finding it hard to cope. It can also help to talk to a close friend or relative about how you feel.
Contact the doctor that arranged the test if you haven't heard anything after a couple of weeks.