What is external beam radiotherapy?

External beam radiotherapy is when a radiotherapy machine aims high-energy rays at the area of the body being treated.

This treatment is normally given as a number of short, daily treatments in a radiotherapy department. These are called treatment sessions or fractions. The radiotherapy machine looks like a large x-ray machine or CT scanner. There are different types of radiotherapy machine. The most commonly used machine is called a linear accelerator (LINAC).

External beam radiotherapy

You usually have external beam radiotherapy as an outpatient. If you are unwell, or are having chemotherapy at the same time, you may need to stay in hospital. In this case, you will go to the radiotherapy department each day from the ward. If you have to travel a long way to the hospital for radiotherapy treatment you may be given it as an inpatient.

Your doctor, radiographer or nurse will explain the treatment plan to you. This includes how many treatment sessions you will have, and when and where you will have them. The number of treatment sessions you have will depend on the type of cancer you have and the aim of the treatment.

The person who operates the machine is called a radiographer. They give you information and support during your treatment.

Types of external beam radiotherapy

There are different ways of having external radiotherapy. How you have treatment will depend on:

  • the type of cancer you have
  • the part of the body that is being treated.

Your clinical oncologist or radiographer can tell you more about these treatments and whether they are suitable for you. If a type of radiotherapy is not available at your local hospital, they may arrange for you to have it at another treatment centre.

  • Conformal radiotherapy

    Many types of external beam radiotherapy are conformal. This means the beams are specially shaped to fit the treatment area. Conformal radiotherapy can be used to treat many different types of cancer.

  • Intensity-modulated radiotherapy (IMRT)

    IMRT is often used to treat many types of cancer. IMRT shapes the radiotherapy beams and allows different parts of the treatment area to have different doses of radiotherapy. This means the healthy tissue surrounding the tumour has lower doses of radiotherapy. This can help reduce the risk of side effects and late effects. It may also allow the tumour to get higher doses of radiotherapy. 

    For example, when used for pelvic tumours, IMRT can reduce the risk of long-term bowel problems. It may also reduce damage to the salivary glands and the risk of permanently having a dry mouth when used for head and neck tumours.

  • Volumetric-modulated arc radiotherapy (VMAT)

    VMAT is a newer way of giving IMRT. It is sometimes called RapidArc®. The radiotherapy machine moves around you and reshapes the beam during treatment. This makes it more accurate and shortens the treatment time.

  • Image guided radiotherapy (IGRT)

    IGRT uses the pictures from scans taken before, and sometimes during, each treatment. The pictures are compared to those taken during the planning scan to check your position and the treatment area. 

    IGRT is helpful for treating tumours in areas of the body that change shape or position during or between treatment sessions. For example, it may be used to treat the prostate or cervix. These organs can change position if you have a full bladder or bowel on the day of your treatment. IGRT means the radiographers can adjust the treatment area before each treatment. This makes the radiotherapy very precise.

  • 4-dimensional (4D) radiotherapy

    4D radiotherapy uses a radiotherapy machine that takes pictures during your treatment. The pictures show any movement of the tumour. Radiographers give the treatment when the tumour is in the correct position in the treatment area. It is sometimes called gating. 

    4D radiotherapy is helpful for treating tumours in areas of the body that move during treatment. For example, these could be tumours in the lung that move as you breathe. The radiotherapy team use the information from the pictures to adjust the radiotherapy treatment area during treatment. 

    There are other ways to help reduce movement in the treatment area. Your radiographer may show you some breathing techniques. Or they may use gentle compression on your tummy area, depending on where you are having treatment. They will do this during planning and treatment. It helps to reduce movement in the area being treated. This allows them to treat the area more accurately.

  • Stereotactic radiotherapy

    Stereotactic radiotherapy uses many small, focused beams of radiation. The beams are directed from different angles that meet at the tumour. This makes it very precise. It means very small areas of the body can get high doses of radiotherapy. This can reduce the risk of side effects. 

    VMAT can also be used to give stereotactic radiotherapy. This means that the radiotherapy machine moves around you and reshapes the beam during treatment.

    Stereotactic radiotherapy is used to treat different types of tumours. You may be offered this treatment as part of a clinical trial.

    This treatment may not be available in all radiotherapy centres. Your radiotherapy team will give you more information if this treatment is suitable for the type of cancer you have.

  • Total body irradiation (TBI)

    TBI treatment is when a large single dose of radiation, or 6 to 8 smaller doses, is given to the whole body. This type of radiotherapy is not used very often. People who are having a stem cell transplant sometimes have it.

  • Proton beam therapy

    Proton beam therapy uses proton radiation rather than x-rays to destroy cancer cells. Proton beams stop when they reach the area being treated. This is different to standard radiotherapy beams, which pass through the area and some healthy tissue around it. Using proton beam therapy may help to reduce side effects and the risk of long-term effects.

    Proton beam therapy is only suitable for a small number of people with certain types of cancer. It is available at:

    Some of these centres only recently began doing proton beam therapy. Until these treatment centres are fully operational, a small number of people who need this type of radiation may be able to have it abroad, paid for by the NHS

    Your radiotherapy team will give you more information if proton beam therapy is suitable for you. You may have to travel to a hospital that offers it.

  • Intraoperative radiotherapy

    Intraoperative radiotherapy is when you have a single dose of radiation during surgery to remove a cancer. You have this in the operating theatre. This treatment is still being researched and may only be available in some centres as part of a clinical trial.

    It may be an option in some situations. For example, it may be used for some people with early breast cancer who would normally have radiotherapy after surgery.

  • Electron beam radiotherapy

    This treatment uses particles called electrons to give radiotherapy to the skin. It treats cancer on the skin or close to the skin surface. This type of radiotherapy does not travel far into your body. Your doctor will tell you if this is an option.

Why am I having external beam radiotherapy?

You may have external beam radiotherapy for different reasons:

Radiotherapy to cure the cancer (curative or radical radiotherapy)

The term radical radiotherapy is used when doctors are hoping to cure the cancer. It usually involves having several treatment sessions. This is called a course of treatment.

You usually have 1 session of radiotherapy a day, often with a rest at the weekends. Some radiotherapy departments give treatment at the weekend. This means you would have rest days during the week instead. For certain types of cancer, treatment is given up to 3 times a day.

The treatment may last between 1 and 8 weeks.

Having the treatment in several sessions means that normal healthy cells have time to recover between treatments. You may have curative radiotherapy:

  • on its own
  • before or after other treatments such as surgery
  • before, after or with other treatments such as chemotherapy, hormone therapy or targeted therapy.

Radiotherapy to treat symptoms (palliative radiotherapy)

If curing the cancer is not possible, you may have palliative radiotherapy. It can help control the symptoms of cancer and sometimes it may help shrink the cancer.

For example, you may have palliative radiotherapy to help:

  • control pain caused by cancer that has spread to the bones
  • reduce coughing caused by cancer in the lungs
  • control bleeding caused by certain types of tumour.

How many treatment sessions you have depends on your situation and the type of cancer you have. You may have 1 to 5 sessions of treatment. Sometimes you may have a course of up to 10 to 15 sessions. For some types of brain tumour, it can be up to 30 sessions.

How is external beam radiotherapy given?

Treatment sessions

Usually, each radiotherapy appointment takes about 10 to 30 minutes. But you may be in the department for longer. The treatment itself usually only takes a few minutes. Most of the appointment is spent getting you into the correct position and checking your details.

Before your first treatment, the radiographers explain what you will see and hear. It is normal to feel a bit nervous. But, as you get to know the staff and understand what to expect, it usually feels less worrying. You can talk to the staff about any worries you have.

Positioning you for treatment

Before your treatment, the radiographer may ask you to change into a hospital gown. This is so they can reach the marks made on your skin at your planning appointment. These show the treatment area.

The radiographers help you onto the treatment couch and position you carefully. They also adjust the height and position of the couch and radiotherapy machine. They will talk you through what they are doing.

The radiographers look at the marks on your skin or on your radiotherapy mask or mould, if you have one. This is to help get you in the same position you were in for your planning scan. They help you arrange your clothes or gown so that the area of your body being treated is bare. They are careful to protect your privacy so that nobody else can see you.

It is important that you are comfortable, as you have to lie as still as possible during the treatment. Tell the radiographers if you are not comfortable. The room may be quite dark to help the radiographers while they are getting you into the correct position.

Your radiographers will tell you how long your treatment will take. When you are in the correct position, they leave the room and the treatment starts.

The radiographers can see and hear you from outside the room. There is usually an intercom, so you can talk to them if you need to during your treatment.

During treatment

The radiotherapy machine does not usually touch you. But for some types of cancer, it may gently press against your skin.

The treatment itself is not painful. You may hear a slight buzzing noise from the radiotherapy machine while you are having the treatment.

In some treatment rooms you can listen to music. This may help you relax. If you would like to listen to your own music, ask your radiographers if this is possible.

Most curative (radical) radiotherapy involves having treatment from several different directions. To do this, the radiotherapy machine may move around you into different positions during your radiotherapy. This may happen several times. You will need to lie still. Sometimes, the radiographers will come into the treatment room to change the position of the machine.

The radiotherapy machine may take pictures (x-rays or CT scans) of the treatment area during your treatment. They may be taken on the first day and again on other days. These pictures are used to help make sure the treatment is given accurately. They are not used to show how well treatment is working, as treatment takes time to work.

After treatment

Once your treatment session has finished, the radiographers will come and help you off the treatment couch. It is important to wait until they tell you it is ok to move. Then you can get ready to go home, or back to the ward if you are having treatment as an inpatient.

External beam radiotherapy does not make you radioactive. It is safe for you to be with other people, including children, throughout your treatment. It is also safe to have sex. 

We have more information about sex and cancer.

Side effects of external beam radiotherapy

Your radiotherapy team plans your treatment carefully to reduce your risk of side effects. But most people have some side effects during or after radiotherapy.

We have more information about the side effects of radiotherapy.

About our information

  • Reviewers

    This information has been written, revised and edited by Macmillan Cancer Support’s Cancer Information Development team. It has been reviewed by expert medical and health professionals and people living with cancer. It has been approved by Senior Medical Editor, Dr David Gilligan, Consultant Clinical Oncologist.

    Our cancer information has been awarded the PIF TICK. Created by the Patient Information Forum, this quality mark shows we meet PIF’s 10 criteria for trustworthy health information.

Date reviewed

Reviewed: 01 August 2022
Next review: 01 August 2025
Trusted Information Creator - Patient Information Forum
Trusted Information Creator - Patient Information Forum

Our cancer information meets the PIF TICK quality mark.

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