Radiotherapy services

Using high energy x-rays to treat cancer 


This page offers a short guide to radiotherapy, the planning process before your treatment and the care you can expect. If you have any questions, please ask a member of your treatment team. 

What is radiotherapy?

Radiotherapy staff member talking to a patientRadiotherapy is the use of high energy x-rays to treat cancer. It damages your body's cells within the treatment area, killing the cancer cells but allowing your normal cells to recover. The side effects are usually confined to the area you are having treated.

Radiotherapy treatment is painless. The experience is similar to having an x-ray or a scan. 

About your treatment

  • Planning your treatment

    Before we plan your treatment, we will ask for your consent, to confirm that you agree to have radiotherapy treatment.

    Radiotherapy planning is used to determine the area to be treated. You will need to have a CT (computerised tomography) scan in the radiotherapy department. We will give you a gown to wear for the scan and ask you to lie on a couch and remain as still as possible.

    After the scan, the radiographers will take some measurements and make some marks on your skin. This acts as a reference to make sure that we treat the same area each time.

    Your planning appointment will take about an hour and before you leave, we will give you the appointments for your treatment. 

  • Having radiotherapy

    Your doctor will prescribe the amount of radiation needed for your treatment. This amount is then divided up into smaller doses (called fractions) that are given over a period of days or weeks. You may just have one visit or lots of visits over six to seven weeks.

    Your treatment will start about two weeks after your planning session. On your first day of treatment, a radiographer (these are the health professionals trained to give radiotherapy) will explain your treatment and possible side effects.

    When you have treatment, you will lie on the couch and the radiographers will make sure that you are lying in the exact treatment position. They will leave the room to switch the machine on, but they are able to see you on a TV monitor outside. 

    You will be in the treatment room for about 15 minutes. If you need help, raise your arm and the radiographers will switch off the machine and return to the room to help you.

  • Other types of radiotherapy


    Brachytherapy, also known as internal radiotherapy works by treating the cancer cells from inside the body. The source of radiation is placed inside or next to your cancer, as the radiation does not travel far. Brachytherapy can be used to treat cancer on its own or in combination with other treatments. Your treatment is carefully designed for you. The number of treatments you have will depend on the type and size of the cancer. For some types of cancer, you will need to make daily trips to the hospital. For others, you will only need to come once. Your doctor will discuss with you how many treatments you need and any special precautions you may need to take. 

    Stereotactic radiosurgery

    Stereotactic radiosurgery is a very precise, non-invasive treatment (not putting any instruments into the body) that uses a high dose of radiation to target small areas of the brain. It can be focused on a very precise point so that it doesn’t damage surrounding healthy tissues. Your doctor will decide with you if this is the best treatment for you. The accuracy of the stereotactic radiosurgery allows radiotherapy to be given over a few sessions using a high dose each day. You will need to have several planning scans, MRI and CT so the doctor can plan your treatment accurately. Treatment usually starts within a few weeks of the planning scans. It can be given as an outpatient appointment meaning you will not need to stay in hospital

  • Side effects

    These are usually only felt in the area that you are having treated and will depend on which part of the body is treated. The radiographers will give you specific information about the side effects you may experience. These might include:

    • a skin reaction
    • hair loss
    • fatigue (tiredness not relieved by resting)
    • constipation or diarrhoea.

    The side effects continue for a while after your last visit and reach a peak about seven to 10 days after you have finished treatment.

Follow-up appointments

You will have a follow-up appointment four to six weeks after your course of radiotherapy ends. We will give you details on how to make this appointment.

Information and support

Being diagnosed with cancer and having treatment can be a difficult and worrying time. You can always ask a member of the team caring for you for support or information.

You can also find sources of support on our Dimbleby Cancer Care page.

Watch a video about our radiotherapy village



Tel: 020 7188 7188 (ext 57542) or

0207 188 3160

If you have a problem in the evening or weekend, please call the main switchboard, ask for 'operator' or dial 0. Then ask the operator for the clinical oncology registrar on call.

Tel: 020 7188 7188.

Other useful contacts

Cancer Centre at Guy's reception:
Tel: 020 7188 7188 (ext 56805)
(8am-8pm, Monday to Friday)

Cancer helpline for our current patients:
0207 188 3754
(8.30am-6pm, Monday to Friday)