Proton Beam Therapy

Proton Beam Therapy (PBT) is a type of radiotherapy that uses beams of 'protons' (energised particles), instead of beams of X-rays ('photons'), that are used in conventional radiotherapy. It is more targeted than conventional radiotherapy so does less damage to the healthy tissue around the tumour and in the rest of the brain.

What is proton beam therapy?

Proton beam therapy is a specialised form of radiotherapy that involves directing a beam of protons (energised sub-atomic particles) specifically at the tumour.

A machine (called a cyclotron or particle accelerator) speeds up the protons causing them to gain energy. Once a high level of energy is reached the protons are then beamed out of the machine and guided by magnets towards the tumour.

Protons accurately release most of their cell-killing energy at a particular depth in tissue. This depth can be varied by the medical team who programme the PBT machine. The beam of protons can be set up to stop once it has 'hit' the tumour cells (and travelled for a safe margin past the tumour to capture any tumour cells beyond the visible edge of the tumour).

This means that proton beam therapy destroys the tumour cells whilst not affecting so many of the surrounding cells. In particular, PBT delivers very little radiotherapy in a path through the rest of the brain on the other side of the tumour, unlike other high energy beams (X-rays) used in conventional radiotherapy.

What is the difference between Proton Beam Therapy and conventional radiotherapy?

This initial damage to the normal cells, however, can cause side-effects in the short-term. Some of the damage may be unrepairable, leading to long-term effects.

Similarly, in PBT the beams of protons are carefully planned to target most of their energy within the tumour.

However, by altering the beam energy, the beam can be designed so that the protons stop and release most of their energy accurately at a particular depth in the brain i.e. where the tumour is situated.

As proton beam therapy is highly targeted towards the tumour, it means it is often possible to treat areas closer to very sensitive structures such as the spinal cord or optic nerve.

Why isn't everyone given proton beam therapy?

Whether your child/you can have PBT depends on many factors, including:

Brain tumour type

PBT is not suitable for all types of brain tumour. It works best for smaller tumours and those where the edges are clearly defined.

It is also useful where the tumour is close to very important structures like the spinal cord or optic nerve, or when it is important to reduce the damage caused to surrounding normal tissue as much as possible e.g. brain tumours in young children whose brains are still developing.

There is a nationally approved list of tumour types that are suitable for referral.

With regards to brain tumours, these include:

Children, teenagers and young adults:

  • ependymoma
  • optic pathway and other selected low grade glioma
  • craniopharyngioma
  • pineal parenchymal tumours (not Pineoblastoma)
  • base of skull and spinal chordoma
  • base of skull chondrosarcoma


  • base of skull and spinal chordoma
  • base of skull chondrosarcoma

Though not on the approved list, PBT has sometimes been used to treat medulloblastomas in children. However, diagnosis alone is not enough. PBT will only be given if it is thought it will give a significant advantage over conventional radiotherapy.

Timing of when the radiotherapy needs to be given

Referral abroad may delay the giving of radiotherapy for longer than the health professionals would advise.

This may not be a such a factor if you/your child is referred to one of the new UK centres.

Timing of when the radiotherapy needs to be given in relation to other treatments

It is most important that PBT seamlessly links with surgery and chemotherapy. Disruption in the pathway, and the resulting delays, can lead to less intensive therapy and a reduction in tumour control. This could counteract any longer term benefits.

This is particularly important in the treatment of high grade, 'malignant' brain tumours, such as medulloblastoma.

Timing may be less of an issue if you/your child is referred to a centre in the UK.

It is also important to realise that:

  • PBT is a relatively new therapy that is usually used for rare types of tumours. This means there is little evidence about its effectiveness compared to conventional radiotherapy, particularly about long-term side-effects
  • the way it works when it reaches the tumour is much the same as conventional radiotherapy
  • the quicker 'stopping' of the radiation in PBT means getting the target right is very important
  • it requires extra training and skill to work out the required depth and dosage of PBT
  • it is harder to check what is actually being treated during PBT treatment - conventional radiotherapy can use imaging to check the accuracy of the treatment area, which is important when near to critical structures, e.g. spinal cord or optic nerve
  • people who travel to receive PBT often respond well, but they are 'optimally chosen' who are more likely to do well

What happens if Proton Beam Therapy is suitable?

If the Clinical Oncologist feels that PBT may be suitable for you/ your child, they will, with your agreement, refer your/your child's case to the Proton Clinical Reference Panel (PCRP) for consideration. This is the same for patients from England, Wales, Scotland and Northern Ireland.

There is a strict set of criteria that a patient must fulfil for a referral for PBT to be made. Funding for treatment will not be approved outside these strict criteria. It is also unlikely that the treatment will be successful if these criteria are not filled.

Referral process

The referral to the panel must be supported by the local MDT (Multi-Disciplinary Team) and made by a Consultant Clinical Oncologist who has seen and assessed you/your child and who has discussed it with you.

The consultant completes a referral form and sends your/your child's medical records, including images of the tumour, to the PRCP. They will decide if PBT will be of more benefit compared to conventional radiotherapy.

This process generally takes at least two weeks, but can be longer if the panel needs to query any of the information they receive. Your consultant will inform you of their decision.

In Scotland the Clinical Oncologist refers first to the Scottish Non-Standard Radiotherapy Advisors, who decide whether to refer on to the PCRP. In Wales, Northern Ireland, the Channel Islands and the Isle of Man, funding also has to be agreed by the local health boards/trusts.

If PBT is approved by the panel, your (or your child's) medical records and tumour images will then be sent by your consultant to one of the approved treatment centres either in the UK or abroad. The treatment centre will discuss and review the case and make the final decision about whether PBT treatment will be offered. They will then inform your health team.

This part of the process can take up to three weeks. Additional tests to help assess your/your child's suitability may be requested. Sometimes further surgery in the UK is also requested before PBT can be offered.

If the treating centre approves treatment, and is abroad, then your local NHS Trust will contact you to discuss travel arrangements and make sure you have the appropriate travel documents (passports, visas, insurance etc.). This part of the process, including arranging travel, can mean it is another three weeks before you arrive at the treatment centre.

Consultations, a planning scan and the actual planning of the treatment will then be done. This can take up to three weeks.

It is important to realise, therefore, that the whole referral process, from when your consultant suggests this could be appropriate treatment to receiving the first PBT, can take nearly three months (11 weeks) if you are sent abroad. It may be quicker if you are sent to a UK centre. Also, at any stage, the case can be refused on the grounds of PBT not being the best option for you/your child.

Where can I have proton beam therapy?

New PBT centres are being built in the UK. Currently (January 2019) they is an NHS centre in Manchester and a private centre in Newport, Wales. These have recently opened so are gradually increasing their capacity. As a result, not all brain tumours suitable for treatment with PBT can be treated in the UK. (Other current UK PBT machines are low energy machines and cannot deliver the protons at a high enough energy to reach the depth in the body where brain tumours are situated.)

However, the NHS will refer appropriate cases to approved treatment centres in the USA or Europe (Switzerland). Children are normally treated in the USA.

There are other (private) centres overseas, but people/parents should be aware that these can be expensive, may not have sufficiently trained staff and often don't offer other treatments, such as chemotherapy, which may be required alongside the PBT. The lack of these additional treatments could have an effect on the overall effectiveness of the treatment.

The NHS is planning to open another PBT centre suitable for treating brain tumours at UCLH (University College London Hospital) in London, which is expected to treat patients by 2020. (Please note that the date may be subject to change.)

Several private companies have also announced they plan to open facilities, in Northumberland, Reading and Liverpool. These are not expected to be able to deliver PBT until later in 2019. (Please note that the dates may be subject to change.) It is also not certain:

  • how many NHS patients will be able to use these private facilities
  • how easy it will be to integrate this treatment with the patient's overall care, which will remain with the main treating hospital (This is particularly important in the treatment of children)
  • whether patients treated there will be able to take part in clinical trials

Will I have to pay for proton beam therapy?

Not if you are approved for treatment by the PCRP. The NHS will cover the cost of PBT treatment at approved treatment centres, whether in the UK or in the USA and Switzerland. If you are sent abroad, it will also fund economy travel and approved accommodation for the patient and one to two carer(s)/parent(s) accompanying them.

The accommodation has to be approved by the treatment centre. The number of carers/parents funded will depend on the age of the patient. If aged over 16 years, only one carer/ parent will be funded, except in exceptional circumstances.

The NHS will NOT fund any meals or refreshments, nor any upgrades to travel or accommodation.

If you live in England, NHS England pays for treatment and your travel and accommodation costs.

If you live in Scotland, NHS England will pay for treatment, plus your travel and accommodation costs, then they claim the money back from NHS Scotland.

If you live in Wales or Northern Ireland, your consultant will contact your local health board/trust directly about funding for treatment, travel and accommodation costs.

If you need help with associated essential costs not covered by the NHS, contact our Support & Info Line about sources of grants and other financial help that may be available, or 0808 800 0004. Alternatively, your local neuro-oncology centre may have access to charitable funding

What else will I need?

If you are sent abroad, the treatment centre you have been referred to will contact you about arranging travel and accommodation and also transport whilst you are abroad.

You will need to make sure you have:

  • up-to-date passports (with at least 6 months travel time remaining)
  • appropriate visas and travel insurance (For the USA, you will need an Electronic System for Travel Authorisation (ESTA) visa, completed at least 72 hours before travel) (Travel insurance will be refunded if you are going to the USA, but not to Europe. In Europe you need a European Health Insurance Card (EHIC) for each person travelling - this entitles you to state-provided medical treatment within the country you are visiting)
  • any medical supplies you/ your child need
  • driving licence (if you intend to drive) and for the USA, an International Driving Permit - you can buy these from the Post Office

How is Proton Beam Therapy given?

The procedure for giving PBT is very similar to conventional radiotherapy.

In preparation:

There will be several planning appointments at the treatment centre before you/your child starts PBT. These include:

  • scans to plan the treatment and programme the machine accurately
  • a radiotherapy mask will be custom-made to keep your child's/ your head still and in position during the PBT sessions. The mask will be custom-made from a mouldable sheet, which is soaked in warm water and laid on your face. It will feel a bit like having a warm flannel across your face. You will wear the mask during PBT sessions to help hold you in position and keep you still. Some centres use tiny beads implanted under the skull (under anaesthesia) to act as pinpoints to ensure the head is located in the same place instead of a mask.
  • the chance to discuss the treatment, what to expect and any possible side-effects

After these appointments there is usually a two week gap whilst the treatment plan is calculated and prepared specifically for you/your child.

The Proton Beam Therapy procedure:

  • Your child (or you) will lie on a treatment couch, and the mask will be placed over their/your face and attached to the couch. You will be positioned correctly. Young children may need to have a general anaesthetic each day of treatment to make sure they stay still.
  • Before the PBT begins, the radiotherapy team will leave the room, but they can still see and hear your child or you. You will not be allowed to stay in the room with your child.
  • A machine called a cyclotron accelerates the protons to high energies. The protons then exit the machine, guided by magnets, towards the tumour
  • Once at the site of the tumour, the protons deposit their energy, destroying the tumour cells
  • After treatment, the team will re-enter the room and help take off the mask

You will then usually be able to go straight home.

The treatment generally only lasts one minute, but with the positioning and adjustments, the session is likely to be about 20 minutes.

It is usually given daily (Monday to Friday) for up to 5-7 weeks. This depends on your child's/your tumour type and grade.

If you are sent abroad, you will need to be away from home for at least 8 – 10 weeks.

Will I need to stay in hospital when having PBT treatment?

No, PBT is usually given as an outpatient treatment, which means you do not need to stay in hospital.

Occasionally, you /your child may need to stay in hospital. For example, if you/your child have side-effects that need inpatient care, or if you/your child need inpatient chemotherapy alongside the PBT.

It is worth bearing in mind, however, that brain tumour patients are often referred to Switzerland or the USA for PBT, which can mean substantial time away from home.

Will proton beam therapy hurt?

The PBT itself shouldn't cause any discomfort, but you may experience some temporary unwanted side-effects following the treatment.

What are the side-effects?

These are likely to be fewer than with conventional radiotherapy, but how your child/you feel will depend on the size of the dose of PBT you had and whether you are having any other treatment, such as chemotherapy.

The following short-term effects are common:

  • fatigue
  • redness that resembles sunburn
    (in the area where the proton beam was directed)
  • hair loss

These are usually temporary and often disappear after treatment has finished.

You will not be radio-active after treatment – it is safe to be around others, including children.

Longer-term effects after PBT in children can include:

  • hearing loss, which can be severe
  • cognitive impairment, particularly thinking speed and understanding language
  • changes in hormone levels, particularly growth hormone

(These effects are also possible with conventional radiotherapy.)

Ask your health team about how to ease any side-effects you or your child experience.

Page last reviewed: 01/2019
Next review due: 03/2020

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