Cancer Research UK on Google+ Cancer Research UK on Facebook Cancer Research UK on Twitter

Scans for radiotherapy

Nurse and patients talking about cancer

This page tells you about the scans you might need when you have radiotherapy. There is information about


CT scans

A CT scan is a special type of X-ray. Like an X-ray, it is painless and you don't feel anything while you have it. This is a photo of a CT scanner.


The machine takes a lot of pictures from different angles and these are put together to give a series of cross sections or slices through the part of the body being scanned.

CT scan

Together, these cross sections give a very accurate picture of where the tumour is and how big it is. They also show how close major body organs are to the treatment area. This means the doctor can plan the radiotherapy to give as low a dose as possible to these organs.

The CT scans can be fed directly into radiotherapy planning computers. CT scans are very helpful when planning radiotherapy treatment because they show the areas that need radiotherapy as well as showing normal tissues and sensitive areas to avoid. They allow the doctors to precisely calculate the dose to the tumour and surrounding tissues.

There is information about how CT scans are used to produce a treatment plan in this section.


MRI scans

MRI scans are made using a powerful magnetic field instead of the X-rays used by CT scanners. Like a CT or X-ray, the scan is painless, but the scanner is very noisy when it is being used. Some people find it a bit claustrophobic inside the scanner.

MRI scanner

The scanner can create pictures as cross sections like the CT scan. The MRI can show other angles too, depending on what is the most helpful for the doctor. MRI scans have been found to be very useful for looking at many types of cancer. They are often combined with CT scans to show the exact size and position of tumours.


PET scans

PET stands for Positron Emission Tomography. This type of scan can show how body tissues are working, as well as what they look like. A PET scan can help to show the size and exact position of some cancers and whether they have spread to other areas of the body. You have an injection of a very small amount of a radioactive drug (tracer). After the injection you rest for about an hour before having the scan. The scan itself can take up to an hour. We have information about having a PET scan in this section.


Bone scans

Bone scans help doctors to see if there are any changes in the bone. They can help doctors to know if cancer has spread to the bones. Cancer that has spread to the bone is often treated with radiotherapy treatment. Bone scans can help doctors to see exactly where to give the radiotherapy treatment.

In a bone scan, a very small dose of radioactive dye is injected into the bloodstream. The dye finds its way to the bones and the radiation is photographed with a special camera called a gamma camera. Any areas where the bone is repairing itself takes up more dye and shows up as a bright area, called a hot spot, on the scan.

Bone scan

Bone scans cannot always tell whether damage to a bone is due to arthritis, a fracture, or from a cancer spreading to the bones. So, sometimes you may need to have other tests, such blood tests, X-rays, CT scans or MRI scans to see whether your cancer has spread. The doctor will also ask you about any symptoms you may have, such as pain.


Other scans

Some people have ultrasound scans before radiotherapy. There are other particular types of scans for certain cancers. For example, you can have a scan for thyroid tissue that uses a small amount of radioactive iodine. Or a test called an MIBG scan for a rare cancer called phaeochromocytoma. Ask your doctor to explain if you need to have a scan that is not mentioned here.

Rate this page:
Submit rating


Rated 4 out of 5 based on 3 votes
Rate this page
Rate this page for no comments box
Please enter feedback to continue submitting
Send feedback
Question about cancer? Contact our information nurse team

No Error

Updated: 2 July 2012