Proton beam therapy could embrace more patients

Proton beam therapy could be made available to a wider group of patients with the help of research focused on accelerating ions with high-powered lasers.

It would negate the need for the huge synchrotron and cyclotron set-ups currently used, which are expensive and not practical for most hospitals.

Particle beam therapy, which uses protons or other ions, is a highly targeted modality of cancer treatment that can precisely irradiate tumours while preserving healthy tissue — especially valuable in brain tumours.

Although the basic technology has been in place since the mid-1980s, its application in cancer medicine has only really come of age in the past decade. However, it is still highly exclusive — the UK has two permanent facilities planned, but NHS patients have been frequently sent abroad for treatment.

Noting rapid advances in the field of laser technology — with peta watts of power available — several research teams, including one at Queen’s University Belfast, began trying to shunt ions at high speed with these lasers. Prof Marco Borghesi, who heads the Queen’s team, explained the basic principles to The Engineer.

‘Simply by focusing one of these laser pulses on a tin foil of any material at high intensity you ionise the material immediately and create a plasma. Energy is then transferred to the electrons, which try to escape from the target, setting up an electrostatic field that can accelerate the ions present on the surface of the material at nearly the speed of light.’

The process has been likened to a wave wake — on which particles can ‘surf’ to very high energies and speed on the back of electrons. Most importantly, the ions can reach great speeds and energies in a matter of centimetres without the huge set-ups required for most particle accelerators.

‘The idea is that it would be possible to create the ions much closer to the patients, so that you can cut down on most of the transport optics and large magnets,’ Borghesi said.

He also said that it would be much easier to change the type of ions used, simply by changing the composition of the foil. Current accelerators generally use protons or carbon ions, but require significant modifications to adapt to different particles.

Nevertheless, Borghesi warned that the laser-driven beams show quite different properties to those currently used and need to be properly characterised. He said the team were now irradiating cell culture specimens with the laser-driven ion beam to see how they react.

Borghesi said that laser-driven ion beams have a wide range of non-medical applications, mostly in the study of complex physics and reactions.