This leaflet answers common questions about having a radiotherapy CT scan with intravenous (IV) contrast.

If you would like further information, or have any worries, please do not hesitate to ask your radiotherapy radiographer or radiotherapy review specialist.

Your radiotherapy radiographer will explain the procedure to you and answer any questions you may have.

In most cases it will be possible for a friend or relative to accompany you for all or part of the procedure. Please ask your radiographer or doctor.

What is intravenous (IV) contrast?

Contrast is a type of dye that allows veins, arteries and some organs and structures in your body to be displayed more clearly on a CT scan and helps with your radiotherapy planning. An IV contrast means that the contrast is injected into a vein.

Before your procedure

When you arrive for your planning CT scan, a radiotherapy radiographer will explain the procedure to you. You may be asked to change into a hospital gown.

The radiographer will complete a questionnaire with you which will tell us what medications you are currently taking and any conditions you may already have. It also aims to identify if you may be at risk of developing a reaction to the contrast dye. On rare occasions reactions may occur. Information is included below about risks and side effects.

Prior to having the CT scan one of the radiotherapy radiographers will place a flexible cannula tube in your arm using a needle to allow the contrast to be injected.

During the procedure

Once you have undergone any necessary preparation for your planning scan and have been positioned on the CT couch, the first part of the scan will be taken. The radiographers will be outside of the room for this but will be always watching you. The CT couch will move a few times while the scan is taking place, but you won’t see or feel anything.

When the contrast needs to be administered, one of the radiographers will re-enter the CT room. They may give an additional flush of saline through the cannula at this stage to ensure it is still positioned as required. They will then connect the contrast injector to the cannula using a long tube and remain with you in the CT room when the injection starts.

You may experience some slight stinging at this stage but let the radiographer know if you experience significant pain or pressure.

When the radiographer is happy that injection is proceeding correctly, they will leave the room. They will need to leave the room quickly before the scan starts, as this must be done within a set time of the injection being given to get the best possible CT image quality.

After your procedure

The radiographers will ask you to wait in the department for 30 minutes to make sure you do not have a reaction to the contrast dye you have been given. If you are feeling okay and have no reaction, you will be able to go home. It is important that you keep yourself hydrated after the procedure and for the next 48 hours. Try to drink two to three litres of water a day during this time.

Risks and side effects

Contrast dye reactions

Reactions to IV contrast are rare but they can happen and range from mild to severe. These may happen immediately or several hours after you have left the department.

Mild reactions

  • Rash/itchy feeling Sneezing
  • Nausea or vomiting

Severe reactions

  • Swelling around the face/neck/throat
  • Difficulty breathing

What should I do if I am having a reaction, but I have left the hospital?

Mild reactions

Call the radiotherapy department and explain that you recently had an IV contrast CT scan and describe the symptoms you are having. The radiographer will provide you with follow-up instructions. Telephone numbers for the department can be found below.

Outside of these hours call your GP or NHS direct on 111.

Severe reactions

Go to your nearest emergency department (A & E) and explain that you recently had a CT scan with an IV contrast injection.