Exploring a laser-hybrid accelerator for radiotherapy

5 September 2022

A multidisciplinary team in the UK has received seed funding to investigate the feasibility of a new facility for ion-therapy research based on novel accelerator, instrumentation and computing technologies. At the core of the facility would be a laser-hybrid accelerator dubbed LhARA: a high-power pulsed laser striking a thin foil target would create a large flux of protons or ions, which are captured using strong-focusing electron–plasma lenses and then accelerated rapidly in a fixed-field alternating-gradient accelerator. Such a device, says the team, offers enormous clinical potential by providing more flexible, compact and cost-effective multi-ion sources.

High-energy X-rays are by far the most common radiotherapy tool, but recent decades have seen a growth in particle-beam radiotherapy. In contrast to X-rays, protons and ion beams can be manipulated to deliver radiation doses more precisely than conventional radiotherapy, sparing surrounding healthy tissue. Unfortunately, the number of ion treatment facilities is few because they require large synchrotrons to accelerate the ions. The Proton-Ion Medical Machine Study undertaken at CERN during the late 1990s, for example, underpinned the CNAO (Italy) and MedAustron (Austria) treatment centres that helped propel Europe to the forefront of the field – work that is now being continued by CERN’s Next Ion Medical Machine Study (CERN Courier July/August 2021 p23).

“LhARA will greatly accelerate our understanding of how protons and ions interact and are effective in killing cancer cells, while simultaneously giving us experience in running a novel beam,” says LhARA biological science programme manager Jason Parsons of the University of Liverpool. “Together, the technology and the science will help us make a big step forward in optimising radiotherapy treatments for cancer patients.” 

A small number of laboratories in Europe already work on laser-driven sources for biomedical applications. The LhARA collaboration, which comprises physicists, biologists, clinicians and engineers, aims to build on this work to demonstrate the feasibility of capturing and manipulating the flux created in the laser-target interaction to provide a beam that can be accelerated rapidly to the desired energy. The laser-driven source offers the opportunity to capture intense, nanosecond-long pulses of protons and ions at an energy of 15 MeV, says the team. This is two orders of magnitude greater than in conventional sources, allowing the space-charge limit on the instantaneous dose to be evaded. 

In July, UK Research and Innovation granted £2 million over the next two years to deliver a conceptual design report for an Ion Therapy Research Facility (ITRF) centred around LhARA. The first goal is to demonstrate the feasibility of the laser-hybrid approach in a facility dedicated to biological research, after which the team will work with national and international partnerships to develop the clinical technique. While the programme carries significant technical risk, says LhARA co-spokesperson Kenneth Long from Imperial College London/STFC, it is justified by the high level of potential reward: “The multi­disciplinary approach of the LhARA collaboration will place the ITRF at the forefront of the field, partnering with industry to pave the way for significantly enhanced access to state-of-the-art particle-beam therapy.” 

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