Proton beam therapy: How it works
Proton beam therapy is a type of radiation treatment used to treat cancerous tumours - but unlike conventional radiation therapy - it can be targeted directly at the affected area.
It means less damage is caused to surrounding tissue, reducing side-effects.
Proton beam therapy is available in the UK only at the Clatterbridge Centre for Cancer NHS Foundation Trust in Wirral, where it is used to treat rare cancers of the eye.