Radiotherapy uses controlled doses of high-energy X-rays to destroy the cancer cells while trying to do as little harm as possible to your normal cells.

When is radiotherapy used as a treatment?

Not everyone with cancer will need radiotherapy. Whether or not it is part of your treatment plan will depend on the type of cancer you have and where it is in your body.

Radiotherapy is sometimes given in combination with other treatments, such as chemotherapy. It is also sometimes given before or alongside surgery to remove a tumour.

How is radiotherapy given?

There are two types of radiotherapy: external radiotherapy and internal radiotherapy. A member of your care team will explain the procedure and help you prepare for it.

External radiotherapy

External radiotherapy is done from outside the body. Having external radiotherapy is a bit like having an X-ray. It’s not painful and will only last a few minutes. The longest part is setting up the machine for your treatment.

It’s important to stay very still during the treatment. You may also need a plastic mould, called an immobilisation device, to help prevent movement in the part of your body that’s being treated.

Radiotherapy is usually given Monday to Friday, with breaks at the weekends and bank holidays. Each day’s dose is called a fraction. Giving the treatment in fractions means that less damage is done to your normal cells. A course of radiotherapy may last anything between one day and seven weeks.

Internal radiotherapy

Internal radiotherapy works from inside the body. It’s based on the idea that cancer cells take up some radioactive substances faster than normal cells do, so can target cancer cells while having less effect on normal cells.

To have this treatment, you might take a radioactive drink or tablet, or it might be given as an injection into your vein or inserted into your body as radioactive wires or pellets.

You will need to stay in hospital until the radioactivity has left your body. During this time you might need to be kept isolated from other people. How long you are in hospital for will depend on your treatment, and it could be just a few hours or up to a few days.

For more information about the side effects of radiotherapy, see our side effects section.

Updated December 2014, next planned review 2017.