Proton beam therapy (PBT) is a form of radiotherapy used to treat certain cancers. It uses high-energy beams of protons, rather than X-rays, to deliver a dose of radiotherapy. It is highly targeted and so reduces the risk of radiation damage to healthy tissues surrounding the tumour. Doctors may use proton beam therapy alone, or, they may combine it with photon radiation therapy, surgery, and/or chemotherapy.

Each patient’s treatment is different and is planned individually. Not all patients would benefit from receiving proton beam therapy. Multidisciplinary teams made up of oncology consultants, surgeons and radiologists carefully consider who will benefit from this treatment.

Proton Beam Therapy causes changes in cells (both normal and cancer/abnormal cells). Cancer cells are more sensitive to radiation than normal cells and so more of them are killed. The normal cells are better able to repair themselves and so the damage to normal cells is mostly temporary. The way that protons behave means that less normal tissue is irradiated, which may result in fewer and less severe side effects during and after treatment.

Proton beam therapy is usually delivered over a course of treatments lasting up to seven weeks. You do not usually need to stay in hospital when you have proton beam therapy. Most patients have their treatment as daily outpatients. Proton beam therapy is usually given Monday to Friday or on a Bank Holiday, but there may be times when your treatment needs to be given over the weekend. This will be discussed with you in advance.

If you have been told you are eligible for accommodation during your proton beam therapy, please follow this link for more information.


CT and sometimes MRI scans are used to create an individual treatment plan for every patient. These scans are used by your doctor and a team of dosimetrists and physicists to produce your treatment plan which is then checked and sent to the treatment machine.

Proton beam therapy is delivered on machines called gantries. You will be asked to lie very still on a couch top. You may also be lying on equipment called immobilisation, which will help you to keep still.

There is nothing to see or feel when you receive your treatment. The machine does not touch you, but it does make a buzzing noise when it is switched on and will move around you.


Treatment times will vary, depending on the area being treated and your specific treatment position. A lot of the time will be spent putting you into the correct position. You will be asked to remove clothing that covers the area being treated, and then lie on a couch in the same position you were planned in. We will provide gowns to maintain your dignity at all times. Using the marks made at your pre-treatment appointment, the radiographers will move the couch and the treatment machine into position.

The machine is only switched on for a few minutes for each beam being delivered.


Proton beam therapy at UCLH

Explaining proton beam therapy