Image guided radiotherapy (IGRT) | Cancer Research UK
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What image guided radiotherapy is

Image guided radiotherapy (IGRT) is a type of conformal radiotherapy. Conformal radiotherapy can shape the radiotherapy beams around the area of the cancer.

Image guided radiotherapy uses X-rays and scans similar to CT scans before and during radiotherapy treatment. The X-rays and scans show the size, shape and position of the cancer as well as the surrounding tissues and bones.

Doctors plan the radiotherapy to give a high dose to the cancer. It is important that the radiotherapy field covers the whole cancer, plus a border around it. This helps the radiotherapy to work as well as possible in treating the cancer. Doctors try to give as low a dose as possible to the surrounding healthy tissue to reduce the risk of side effects.


Types of image guided radiotherapy

In some areas of the body, tumours may be in a different place for each treatment. An example is the prostate gland, which changes position according to whether the bladder is full or not. So there is a risk that part of the tumour may be outside the radiotherapy field during some treatment sessions. With some types of IGRT the radiographers can take scans using the radiotherapy machine before each treatment. Then they can make sure the cancer is within the radiotherapy field each time.

With some types of image guided radiotherapy, the radiographers can take scans with the radiotherapy machine during treatment. So they can make sure the cancer is within the radiotherapy field throughout each treatment session. They call this 4 dimensional (4D) radiotherapy (4D-RT). The 4th dimension in this case is time. 4D-RT can adjust to any changes in the position of the tumour during the time the radiotherapy is being given.

In some types of 4D-RT the machine may switch off if the tumour 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 lung. The radiation beam switches on again when the tumour moves back into a certain position which can be seen on the scan.


Benefits and possible drawbacks of IGRT

With image guided radiotherapy, doctors can target the radiotherapy treatment very accurately. This can mean that the treatment works better in curing or controlling a cancer. It can also reduce the risk of side effects. The drawback is that planning the treatment may take longer. Each radiotherapy session also takes longer.


Planning image guided radiotherapy

Planning image guided radiotherapy treatment involves several steps.

You start with a session in the radiotherapy department. You have a CT scan. The 360° photo is of a CT scanner. Use the arrows to look around the room.

You may also have MRI scans or PET scans of the area of the body to be treated.

The information from these scans feeds directly into the radiotherapy planning computer.

The computer programme then designs radiation beams that follow the shape of the tumour very closely. They make sure that the whole cancer is inside the radiotherapy field and healthy tissue is avoided as far as possible. This reduces the risk of side effects.

Skin markings

The radiographers may make marks on your skin to make sure the same area is treated at each session. See our information about skin markings.

Moulds and masks

If you are having conformal radiotherapy to your head or neck, you may need to wear a plastic mould during your treatment. You may hear this called a shell or mask. Some types of mask are see through, others aren't. You can have a mould for other parts of the body, such as the breast, limbs and sometimes the whole body.

The mould or mask keeps the treatment area completely still. So your treatment will be as accurate as possible. This also means that you can have any markings you need made on the mask, instead of on your skin. See our information about radiotherapy moulds.

Metal markers

Your doctor or radiographer may ask you to have small metal markers (fiducial markers) put in or near your tumour. For this your doctor inserts a needle into the area of skin over the tumour. They do this while you are having an X-ray or CT scan. Once the tip of the needle is in the right place they release a small gold pellet or rod. The radiographers can then see the markers on X-rays and scans while you are having your treatment. This makes sure that the treatment is targeted very precisely.


After the planning session

After the planning session you usually have to wait for 2 weeks or more for the physicist and your radiotherapy doctor to create your treatment plan. You then get an appointment for your first dose of radiotherapy.


Having image guided radiotherapy

To have the treatment you lie on a radiotherapy couch. The radiographers will help you to get into the right position and put on any moulds that you may need.

IGRT is commonly given by standard radiotherapy linear accelerator (LINAC) machines that have been specially adapted and have particular computer programmes.

A photo of a linear accelerator, which gives radiotherapy

Some types of image guided radiotherapy use specially designed radiotherapy machines. The CyberKnife machine gives image guided stereotactic radiotherapy. It has a robotic arm that moves around the patient. The arm gives the radiotherapy from many different angles. We have information about stereotactic body radiotherapy.

A Tomotherapy machine gives image guided intensity modulated radiotherapy. It combines a CT scanner and an external beam radiotherapy machine. Part of the Tomotherapy machine can rotate completely around the patient to take CT scans and give radiotherapy to a very localised area.

Once you are in the right position the staff leave you alone in the room. This is so they are not exposed to the radiation. The staff watch you carefully either through a window or on a closed circuit television screen. They may ask you to hold your breath or take shallow breaths during the treatment.

You can't feel radiotherapy when you actually have the treatment. It doesn’t hurt. It may take from 15 to 45 minutes.


Possible side effects

With image guided radiotherapy techniques there is less normal tissue in the field of the radiotherapy than with some other types of radiotherapy. So the risk of side effects is lower. But unfortunately you can still have side effects. As with any external beam radiotherapy, the side effects only affect the part of the body that the radiotherapy treatment is aimed at.

There is more information about side effects of radiotherapy in the radiotherapy section.


More information about radiotherapy

We have general information about radiotherapy in our radiotherapy section.

We have information pages about other types of radiotherapy including

You can phone the Cancer Research UK nurses on freephone 0808 800 4040. The lines are open from 9am to 5pm, Monday to Friday. They will be happy to answer any questions that you have.

Our general organisations page gives details of people who can provide information about radiotherapy. Some organisations can put you in touch with a cancer support group.

Our cancer and treatments reading list has information about books, leaflets and other resources about radiotherapy treatment.

If you want to find people to share experiences with online, you could use Cancer Chat, our online forum.

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Updated: 28 April 2014