What is a CT scan?
A CT scan is a group of x-ray images taken together to show a detailed picture through part of your body. The scan shows the treatment area including the tumour as well as any surrounding internal organs in that part of your body.
Why do I need a scan?
A CT scan is used to collect the information about your body and the area to be treated. This is important as the pictures collected during your scan will be used to plan exactly how to deliver your radiotherapy.
Note: If you are diabetic, pregnant or have an implanted device such as a pacemaker or cardiac defibrillator please inform the staff at the time of booking the scan.
How does a CT scanner work?
A CT scanner is a special x-ray machine that is shaped like a donut. An x-ray tube spins around the hole in the scanner collecting x-ray images. While the machine is on, the table you lie on moves through the scanner. It is not a tunnel, and you will not be completely surrounded by the CT scanner. The images are collected by the computer and joined together to create a CT scan.
Do I need to prepare for the planning CT scan?
Depending on the area to be treated, you may be asked to prepare for your scan. If you are required to do something before arriving for your appointment you will be given instructions.
Note: If you feel claustrophobic or worried about the small scanner space, please let the radiation therapist or your doctor know before you come for your scan. There are a few ways to help you cope with your anxiety and/or claustrophobia.
What happens during your planning CT scan?
- The radiation therapist will take you to the scanning room and you may be asked put a gown on. You must remove jewellery and metal objects such as hair clips from the area being scanned as metal will affect the quality of the CT scan. If you are unsure, ask the radiation therapist.
- You will be placed in the position in which you will be treated each day. When you are in the correct position the radiation therapists will leave the room to start the scan. They will watch you on a monitor from outside the room. You will be able to speak to them via a microphone if needed.
- During the scan you will be asked to breathe normally and try to relax.
- Once the scan is complete the radiation therapists will add some reference marks to your mask or to your body as tattoos (see below). They may also take some measurements and photos which are used each day for your treatment set up.
A plastic mask may be made for some treatments (eg to the brain or head and neck areas). This will be done before the scan and the radiation therapists will explain this to you.
Tattoos for radiotherapy are a reference mark used to set you up for treatment each day. The radiation therapist will place a small amount of ink on your skin, and then use a small needle to put the ink under a couple of layers of skin. It feels like a tiny pin prick and will leave you with a small freckle like mark.
How long does a planning CT scan take?
The scan itself will take approximately 1-2 minutes depending on the area of your body that needs to be scanned. You will be on the scanner for about 30-45 minutes in total. The majority of this time is used to set you up in your treatment position and record the details of the position for your treatment. If you find it hard to lay still in this position let the radiation therapist know before the start of the scan, as it is important that you are able to lay still for your planning scan and treatment.
Intravenous (IV) contrast
Some scans are done using a dye called ‘contrast’, this is given as an injection into a vein through a small drip (or cannula). This dye is used to make the internal organs and tissues more visible to the scanner. If contrast is to be used for your scan you will be given more information about this before your appointment. If you have any allergies, asthma or are taking any medication it is very important that you tell the doctor and your radiation therapist before the scan.
It can sometimes cause a metallic taste in the mouth, a warm/hot sensation throughout the body or a sensation that you have passed urine. This feeling usually passes after a couple of minutes.
If you have had contrast for your CT scan, you will need to stay in the department for a period of time after your scan so you can be monitored in case you have a reaction to the dye.
Does a CT scan hurt?
The CT scan itself does not hurt.
Will I feel anything during my scan?
You will not see or feel anything during your scan. You will hear the scanner making a whirring sound as the x-ray tube spins around during the scanning process.
Are there possible risks from a planning CT scan?
You should not have a CT scan if you are pregnant as the radiation from the CT scan may harm an unborn baby. There is a rare chance that you may have an allergic reaction to the contrast if it is used. The reaction often starts with a weakness (feeling faint), sweating and difficulty breathing. If this occurs during your scan let the radiation therapists know straight away so they will stop the scan and treat the reaction immediately.
After having contrast with your CT scan if you experience weakness, sweating, develop a rash or have difficulty breathing, IMMEDIATELY call '000', go to your nearest hospital Emergency Department, or contact your doctor or nurse.
CT Scanner and mask