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Image guided radiotherapy (IGRT)

Image guided radiotherapy (IGRT) uses scans and x-rays to make sure that you're in the correct position for your radiotherapy treatment. Your radiographers (sometimes called radiotherapists) take them on the radiotherapy couch once you're in the right position, just before they switch the radiation beam on. They then check them against your scan taken at your planning appointment. 

They might move the radiotherapy couch or your position after looking at the x-rays and scans. This is to make sure you're in a position very close (within millimetres) to your planning scan.

Sometimes you might have an x-ray or scan taken just after your treatment. You stay in the same position for this and it's used as another check. 

X-rays show your bones in the treatment area. And scans show the size, shape and position of the cancer as well as the surrounding tissues and bones.

CT scan cross section
An example of a scan

How does IGRT help?

In some areas of the body, cancers may move slightly during or between treatments. For example, the prostate gland changes position according to whether the bladder is full or not.

You might also lie down in a slightly different position each day. 

So there is a risk that part of the cancer may be outside the treatment area (radiotherapy field) for some treatment sessions. 

Taking scans and x-ray just before your radiographers switch the radiotherapy treatment beam on makes sure that you are in a position very close to your planning scan.  

If your radiographers see that from your first few images that you're position is very similar each day then on some days you might not have images taken. 


4D-RT involves images being taken during your treatment. The radiotherapy machine can then adjust the position of the couch using information from the images.

In some types of 4D-RT the machine may switch off if the cancer moves out of the radiotherapy field. This type of treatment is helpful for cancers in areas of the body that move when we breathe, such as the lungs. The radiation beam switches on again when the cancer moves back into the right position. Your radiographers are always in control of the radiotherapy machine. 

Having IGRT

Most external radiotherapy machines can deliver IGRT. A linear accelerator (LINAC) is the most common radiotherapy machine.

To have the treatment you lie on a radiotherapy couch. Your radiographers help you to get into the right position and put on any radiotherapy moulds or masks. 

Photo of a linear accelerator
A photograph of a LINAC machine

Once you are in the right position your radiographers leave you alone in the room. This is so they are not exposed to the radiation but they can see and hear you the whole time. 

They usually take x-rays and scans before your treatment. They make sure the treatment field is in the correct place by a few millimetres. Your radiographers might not take x-rays and scans for all of your treatments. This can vary depending on what type of cancer you have and how stable your position is.

You can't feel anything when you have the treatment. It doesn’t hurt. It takes between 15 to 45 minutes.

Metal markers

Your doctor or radiographer may ask you to have small metal markers (fiducial markers) put in or near your tumour. This is common for prostate cancer.

To place the markers, your doctor inserts a needle into the area of skin over the cancer. They do this while you are having an ultrasound scan. Once the tip of the needle is in the right place your doctor releases a small gold pellet or rod.

Your radiographers can then see the markers on x-rays and scans while you're having treatment. They act as a marker for the treatment area, and makes sure that the treatment is very accurate. Your radiographers will take either x-rays or scans every day before treatment if you this type of metal markers. 

Possible effects of IGRT

With IGRT, doctors can target the radiotherapy treatment area very accurately. So that there is less radiation to nearby healthy tissues. This can reduce your chance of side effects from radiotherapy. 

But taking images during treatment can increase the length of time that you're on the radiotherapy couch, which may be uncomfortable. And having extra scans and x-rays also slightly increases the amount of radiation that you're exposed to.

It's important to remember that this is still a very small amount compared to your treatment dose. Your doctor and radiographers make sure the benefits of taking the images outweigh the risks. This is the reason why you might not have scans and x-rays taken every day. 

Last reviewed: 
02 Jan 2019
  • External Beam Therapy (2nd edition) 
    Peter Hoskin
    Oxford University Press, 2012

  • Devita, Hellman and Rosenberg's Cancer Principles and Practice of Oncology (10th edition)
    VT Devita, TS Lawrence and SA Rosenberg
    Wolters Kluwer Health, 2015

  • Advances in radiotherapy
    S Ahmad and others
    British Medical Journal, 2012.

  • National Radiotherapy Implementation Group Report – Image Guided Radiotherapy (IGRT) guidance for implementation
    NHS National Cancer Action Team, August 2012

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