What is proton beam therapy?

Proton beam therapy is a type of external beam radiotherapy

Proton beam therapy is only suitable for a small number of people with certain cancer types. It is used to help reduce the risk of long-term side effects that can sometimes develop after standard radiotherapy. It can also be used to treat cancers that are close to important parts of the body.

These cancers may be difficult to treat with standard external beam radiotherapy.

Proton beam therapy is given using specialised equipment that is not available in all UK hospitals. You may be referred to a specialist hospital if your cancer doctor thinks it is a suitable treatment for you.

How does proton beam therapy work?

Radiotherapy uses high-energy rays called radiation to treat cancer. It destroys cancer cells in the area where the treatment is given. The aim is to:

  • stop the cancer cells growing
  • shrink the cancer or completely destroy it.

Standard radiotherapyy uses high-energy x-rays. The radiotherapy is carefully aimed at the cancer, but it passes through some normal cells to reach the cancer. Some of the normal cells are damaged by the radiotherapy. This may cause side effects. Most side effects are temporary.

Proton beam therapy uses protons instead of x-rays. Protons are parts of atoms. The protons are shaped into a beam that is targeted at the cancer. The proton beam passes through normal cells releasing only a little energy until it reaches the cancer. When it reaches the cancer, the proton beam slows down and stops. The protons then release a large amount of energy, which damages the cancer cells. But there is less damage to normal cells beyond the cancer.

Proton and phototon
Image: Proton and phototon

You can watch a video about how proton beam therapy works on the NHS England website.

When is proton beam therapy used?

Proton beam therapy is not suitable for everyone. It can be used to treat children, teenagers, young adults and some adults (see below).

Proton beam therapy may be given on its own or in combination with other treatments. For example, it may be given with surgerystandard radiotherapy and chemotherapy.

Proton beam therapy is still quite a new treatment in the UK. Research is needed to find out more about its long-term benefits and side effects, and to compare it with standard treatments.

It is also important to remember that when treating most types of cancer, standard radiotherapy is a very effective and safe treatment. Standard radiotherapy can cause side effects, but they usually get better when the treatment has finished.

Your healthcare team will give you more information if proton beam therapy is suitable for you. It may be given as part of a clinical trial. We have more information about clinical trials.

Children, teenagers and young adults

Proton beam therapy may be used to treat children, teenagers and young adults. It can be better for these groups than standard radiotherapy, because it:

  • reduces the risk of damage to developing or growing cells
  • can help reduce the risk of long-term effects on normal cells, such as to the brain or bones.

It is used to treat most tumours that need curative radiotherapy in young people. Examples include:

  • brain tumours
  • types of soft tissue sarcoma, such as rhabdomyosarcoma
  • types of primary bone cancer, such Ewing’s sarcoma
  • some types of cancers in the pelvic area
  • some types of cancers in the head and neck area.


Proton beam therapy can also be used to treat adults with cancers:

  • that can be difficult to treat because of where they are in the body
  • that are in a position where the side effects of standard radiotherapy would cause serious problems
  • where there is a high risk of late side effects from standard treatments
  • that do not respond well to standard radiotherapy and would need a very high dose of treatment to be effective.

It can also be used to treat cancers that are close to important structures. These can include:

  • cancers affecting the base of the skull
  • cancers affecting the spine
  • some types of cancers in the pelvis
  • some types of head and neck cancers

Low-dose proton beam therapy is also commonly used to treat cancers affecting the eye, such as ocular melanoma.

Proton beam therapy may sometimes be used to treat other cancers.

Planning your proton beam therapy

Before you start your treatment, it needs to be planned. This is to make sure the proton beam therapy:

  • is aimed precisely at the cancer
  • causes the least possible damage to nearby normal cells.

Proton beam therapy is planned for each person by a clinical oncologist and a specialist proton beam therapy team.

It is important to tell the hospital staff about any medications and allergies you have. If you take painkillers, they may advise you to take them before your planning and treatment. This can make you more comfortable.

You will spend around 3 to 5 days at the proton centre having the tests you need to plan your treatment. You will then go home until the treatment plan is ready. This can take 3 to 4 weeks. When it is ready you will return to the centre to start your treatment. If you live far away, you may need to stay at the proton centre until you finish your treatment. The centre will provide accommodation.

Radiotherapy masks and moulds

You may need to have a radiotherapy mask or mould made before planning starts. This is to help you stay still and in the correct position during your proton beam therapy.

Masks keep your head and neck area still. They are often used for planning and treatment to the brain, head and neck or upper chest area. Sometimes they are called thermoplastic shells or immobilisation devices.

Moulds are used to keep a leg, arm or other body part still during planning and treatment. Your doctors will tell you more about this if you need one.

We have more information about radiotherapy masks.

A radiotherapy room
Image: MACP058_Radiotherapy Room.268

Imaging and planning

You usually start planning by having a CT scan. You may also have an MRI scan.

These scans build up a detailed picture of the area to be treated. A clinical oncologist will mark on the scans the area to be treated and healthy tissue to try and avoid. A physicist then plans your treatment with your clinical oncologist. A computer uses the information from the scans to make an individual plan for your treatment.

This makes sure the proton beam therapy is precisely targeted at the cancer which helps reduce the risk of side effects. This plan is checked by members of the radiotherapy team to make sure it is safe.

Skin markings

You may have markings made on your skin. These help the radiographers position you for treatment.

Usually, tiny permanent markings are made in the same way as a tattoo. The marks are the size of a pinpoint. It can be a little uncomfortable while they are being made. But it makes sure the treatment is directed accurately. If you have a mould or radiotherapy mask, the marks may be made on this.

These marks will only be made with your permission. If you are worried about them or already have a tattoo in the treatment area, tell your radiographer. They can discuss this with you.

Pacemakers and implantable cardiac devices

If you have a pacemaker or an implantable cardiac device (ICD), you must tell your cancer doctor when you discuss treatment. You should also tell your radiographer, either before or during your first planning appointment.

Proton beam therapy can affect these devices, so your treatment needs to be planned to allow for them. Your cardiology team should also check the pacemaker or ICD.


It is important that you do not get pregnant during your treatment. This is because proton beam therapy given during pregnancy could harm a developing baby. Your doctors will be able to give you more information about this.

If you think that you may be pregnant at any time during your treatment, tell the doctors and radiographers straight away.

Making someone pregnant

It may also be important that you do not make someone pregnant during treatment, and for a few months after it has finished. You can ask your doctors for more information about this.


Your ability to get pregnant or make someone pregnant is called fertility. If this is important to you, talk to your doctor or nurse before you start treatment.

We have more information about fertility for men and women.

Having proton beam therapy

Treatment sessions

You usually have proton beam therapy as an outpatient. The number of treatments you have will depend on the type of cancer you have. You usually have 1 session of treatment a day from Monday to Friday, with a rest at the weekends. The treatment normally lasts for 3 to 8 weeks. This is called a course of treatment. Your cancer doctor, specialist nurse or radiographer will explain the treatment plan to you.

Each appointment usually takes about 30 to 60 minutes, although you may be in the department for longer. The treatment can take up to 30 minutes to deliver. Most of the appointment is spent getting you into the correct position and doing checks.

Positioning you for treatment

Before your treatment, the radiographers help you on to the treatment couch and position you carefully. They also adjust the height and position of the couch. It is important you are comfortable, as you have to lie as still as possible during the treatment. Tell the radiographers if you are not comfortable.

Young children who are having proton beam therapy may have a general anaesthetic to help them lie still during each treatment. The anaesthetic only lasts for a short time. They may also have an anaesthetic if they are very anxious. Sometimes a play specialist comes to the treatment session to help them keep calm and still.

Before each treatment, you have a CT scan or x-rays in the treatment room. This makes sure you are in the correct position.

When you are in the correct position, the radiographers leave the room and you start your treatment. There is a camera, so they can see you from outside the room. There is also an intercom, so you can talk to them if you need to during your treatment.

You may have more CT or MRI scans during your course of treatment. This is to make sure the treatment is always accurately aimed at the cancer. The radiographers will tell you if you need to have more scans.

During treatment

Proton beam therapy machines have a part called the gantry. This moves around you to give the treatment from different angles. Or sometimes the treatment couch moves around and the machine stays still.

The movements are controlled by the radiographers from outside the room. The radiotherapy machine does not touch you. The treatment itself is painless.

When 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 okay to move. You can usually go home when the treatment is finished.

Proton beam therapy does not make you radioactive. It is safe to be with other people, including children, throughout your treatment.

Possible side effects of proton beam therapy

Proton beam therapy may cause fewer side effects than standard radiotherapy. This is because normal cells are exposed to less radiation. The possible side effects will depend on:

  • the area of your body being treated and what structures are close by
  • the amount of proton beam therapy you have
  • other treatments you are having, such as chemotherapy.

Below are some of the side effects of proton beam therapy. Not everyone will get side effects. It is difficult to know exactly how you will react to treatment. Your team will explain what to expect. Always tell them if you have side effects during or after proton beam therapy. They can give advice and support to help you cope.

General side effects

Side effects usually develop over time. They can include the following:

  • Tiredness – you may feel tired during treatment and for a few weeks after the treatment has finished.
  • Skin reactions – your skin may darken, become red, dry or itchy. Sometimes the skin can blister or peel. Skin reactions can be worse with proton beam therapy than with standard radiotherapy.
  • Hair loss – you may lose hair in the area being treated.

These side effects are usually mild and get better a few weeks after treatment has finished.

Long-term and late effects of proton beam therapy

Most types of radiotherapy cause side effects that develop during treatment and slowly improve after treatment has finished. But sometimes side effects do not go away, or they start months or years after treatment has ended. These side effects are called:

  • long-term effects – if they begin during treatment, or shortly after treatment has ended, and do not go away
  • late effects – if they begin months or even years later, as a delayed response to treatment.

The possible late effects of proton beam therapy depend on the area of the body that is treated. Your cancer doctor, specialist nurse or radiographer can give you more information.

Children may get different late effects to adults. This is because they are still growing. Children and teenagers are more likely than adults to develop late effects after proton beam therapy.

At the moment, proton beam therapy is only used to treat a few types of cancer. We only know about some of the potential late effects of treatment for these cancers.

More research is needed to find out if proton beam therapy causes late effects when used to treat other types of cancer. If you are worried about the risk of late effects, talk to your cancer doctor or specialist nurse.

Second cancers

As with standard radiotherapy treatment, proton beam therapy can increase the risk of developing a second cancer. But the risk of a second cancer is lower with proton beam therapy than with standard radiotherapy treatment.

This risk is far less than the benefits of treating the first cancer with radiotherapy. If you are worried about your risk of developing a second cancer, talk to your cancer doctor.

Is proton beam therapy available in the UK?

Low-energy proton beam therapy is available at the Clatterbridge Cancer Centre in Wirral to treat tumours of the eye.

High-energy proton beam therapy has been available at the Christie Hospital in Manchester. It recently became available at University College Hospital in London. This will be for a small number of people to begin with. 

Your specialist team will give you more information if proton beam therapy is suitable for the type of cancer you have. If you do not live close to these centres the NHS may fund accommodation so that you can live nearby the hospital while having treatment. Your cancer doctor or nurse can give you more information about this.

Until these treatment centres are fully operational, a small number of people who need this type of treatment may be able to have it abroad, paid for by the NHS.

Proton beam therapy is also available in the UK at private treatment centres. This is not funded by the NHS.

Benefits and disadvantages of proton beam therapy

Proton beam therapy may cause fewer side effects for some cancers, but we do not know if it is better than standard radiotherapy or other treatments. Proton beam therapy has only been used to treat a few different types of cancer in the UK.

More research is needed before we know if proton beam therapy is as good as, or better than, standard radiotherapy or other treatments.

Possible benefits

The benefits of proton beam therapy include:

  • It can be used to treat cancers that are close to important parts of the body. These cancers can be difficult to treat with standard radiotherapy.
  • It may cause fewer side effects than standard radiotherapy. This is because there is less damage to normal cells.
  • It may be possible to give higher doses of treatment, without increasing side effects.
  • It may help reduce the risk of developing long-term or late side effects.
  • It may help reduce the risk of developing a second cancer.


Disadvantages of proton beam therapy include:

  • It is only suitable for certain types of cancer.
  • The 2 NHS proton centres in the UK are in London and Manchester. If you live far away from these you may need to stay closer for your treatment.
  • The therapy is much newer than standard radiotherapy and more research is needed to understand the differences.

    For example, we do not know the differences between possible late effects of standard radiotherapy and proton beam therapy.

  • People treated with proton beam therapy will still have some side effects.

Your cancer doctor or specialist nurse will talk to you about your treatment options. If proton beam therapy is suitable for you they will talk to you about the possible benefits and disadvantages. This will help you decide whether to have proton beam therapy or another type of treatment.

Getting support

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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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