A hydrogen atom consists of a proton and electron. When the atom loses an electron through ionisation the remaining nucleus, or proton, is positively ‘charged’. This enables proton beams to be focused and accelerated by magnetic and electric fields.
The cyclotron was one of the earliest types of particle accelerator, or ‘atom smashers’, developed for nuclear physics in the 1930s. Within a decade they were being used for diagnostic and therapy purposes. The cyclotron uses a powerful magnetic field to ‘extract’ protons from the cyclotron tank and form them into a beam, which is then ‘piped’ into the treatment room.
Most therapeutic radiation doses (photons, X-rays and electrons) decrease as they go deeper into tissue, meaning the dose is uneven. Proton beams stop sharply at a pre-determined depth, offering a flat dose over the tumour volume.
Proton beams are scattered very little as they travel through tissue, and so have sharp edges. They travel for fixed distances and then come to an abrupt halt. This means that the protons’ energy is deposited precisely where required, so a tumour can be irradiated completely whilst avoiding sensitive parts of the eye. In effect, they can be described as a ‘bespoke’ radiation.
The National Centre for Eye Proton Therapy at The Clatterbridge Cancer Centre is the only one in the United Kingdom that can provide this kind of therapy. We have an excellent history and reputation for treating patients with various forms of eye cancer and our success rate is extremely high.