What is proton beam therapy?

Wednesday September 3 2014

Proton beam therapy has been discussed widely in the media in recent days.

This is due to the controversy surrounding the treatment of a young boy called Ashya King, who has medulloblastoma, a type of brain cancer.

Ashya was reportedly taken abroad by his parents to receive proton beam therapy.

But what does proton beam therapy involve, and can it treat cancer effectively?

How does proton beam therapy work?

Proton beam therapy is a type of radiotherapy.

Conventional radiotherapy uses high energy beams of radiation to destroy cancerous cells, but surrounding tissue can also be damaged. This can lead to side effects such as nausea, and can sometimes disrupt how some organs function.

Proton beam therapy uses beams of protons (sub-atomic particles) to achieve the same cell-killing effect. A "particle accelerator" is used to speed up the protons. These accelerated protons are then beamed into cancerous cells, killing them.

Unlike conventional radiotherapy, in proton beam therapy the beam of protons stops once it "hits" the cancerous cells. This means that proton beam therapy results in much less damage to surrounding tissue.

Who can benefit from proton beam therapy?

Proton beam therapy is useful for treating types of cancer in critical areas – when it is important to reduce damage to surrounding tissue as much as possible. For example, it is used most often to treat brain tumours in young children whose brains are still developing.

Proton beam therapy can also be used to treat adult cancers where the cancer has developed near a place in the body where damage would cause serious complications, such as the optic nerve.

These types of cancer make up a very small proportion of all cancer diagnoses. Even if there was unlimited access to proton beam therapy, its use would not be recommended in most cases.

Cancer Research UK estimates that only one in 100 people with cancer would be suitable for proton beam therapy.

Is proton beam therapy effective?

It is important not to assume that newly emerging treatments are more effective than existing treatments.

Proton beam therapy may cause less damage to healthy tissue, but it is still unclear whether it is as good at destroying cancerous tissue as conventional radiotherapy.

As proton beam therapy is usually reserved for very rare types of cancer, it is hard to gather systematic evidence about its effectiveness when compared to radiotherapy.

People who travel abroad from the UK to receive proton beam therapy usually respond well. But these people have specifically been selected for treatment as they were seen as "optimal candidates" who would benefit the most. Whether this benefit would apply to more people with cancer is unclear.

We cannot say with any conviction that proton beam therapy is “better” overall than radiotherapy.

Is proton beam therapy available in the UK?

Generally not. The NHS is building two proton beam centres, one in London and one in Manchester, which are expected to open in 2018. There is an existing low energy proton machine used specifically to treat some eye cancers at the NHS Clatterbridge Cancer Centre in Merseyside. This low energy machine cannot be used to treat most brain tumours as the low energy beam cannot penetrate far enough.

The NHS sends patients abroad if their care team thinks they are ideally suited to receive proton beam therapy. Around 400 patients have been sent abroad since 2008 – most of these patients were children. Read NHS England's advice for families of children being referred for proton beam therapy at overseas clinics (PDF, 1.39Mb).

Some overseas clinics providing proton beam therapy heavily market their services to parents who are understandably desperate to get treatment for their children. Proton beam therapy can be very costly and it is not clear whether all children treated privately abroad are treated appropriately.

It is important not to lose sight of the fact that conventional radiotherapy is, in most cases, both safe and effective with a low risk of complications. While side effects of radiotherapy are common they normally pass once the course of treatment has finished.

Edited by NHS Choices