The ultimate aim is for CERN to establish itself as an important facilitator of medical physics in Europe. "Since the start of this year, we are trying to combine all of our research on medical applications at CERN into one coordinating office," explained CERN's Director-General Rolf Heuer, speaking at the recent ICTR-PHE meeting in Geneva, Switzerland.

Heading up the office for medical applications is Steve Myers, formerly CERN's director of accelerators and technology. Myers' first task in his new role was to set up a brainstorming workshop to help guide the direction of the fledgling programme. The workshop, which took place immediately after the ICTR-PHE meeting, saw around 80 experts from around the globe come together to discuss matters such as accelerators and gantries, clinical perspectives, biomedical research and radioisotope production, detectors and dosimetry, and the application of large-scale computing.

"From a structure point-of-view, it's difficult. We have biologists, physicists, accelerator physicists, medical doctors, and we have to get all of these people together to collaborate," Myers said. "One of the last sessions of the weekend asks 'what is the best collaborative structure?' and 'where are we going to get funding from?' We've had a very positive response – we had the leading experts from Europe and the US, and in addition we had five top experts from Japan coming solely for this meeting."

The LEIR conversion

One of the first projects that Myers will oversee is the transformation of CERN's Low Energy Ion Ring (LEIR) into a biomedical facility. LEIR is a small accelerator currently used to pre-accelerate lead ions for injection into the Large Hadron Collider (LHC). But it only does this for several weeks each year, leaving a lot of spare beam time. Importantly, the ring also has an energy range that matches that of medical accelerators (440 MeV/u for carbon ions).

CERN has now confirmed that LEIR can be converted into a dedicated facility for biomedical research. This "BioLEIR" facility will provide particle beams of different types at various energies for use by external researchers. Conveniently, there's also a 54 x 27 m hall next to LEIR, currently used for storage, which could be developed into laboratory space.

Myers explained the rationale for developing such a facility. He pointed out that although protons and carbon ions are already in extensive clinical use for treating tumours, and other species such as oxygen and helium ions are under investigation, there's still a lack of controlled experiments that directly compare the effect of different ions on cancer cells under identical conditions.

And while existing clinical centres may well intend to perform such studies, once patient treatments begin, free accelerator time for research becomes extremely limited. "The big advantage here is that we don't treat patients," said Myers. "Our aim is to provide a service, so researchers don't have to do experiments at a clinical site, they can come here instead."

As well as radiobiology experiments, LEIR is lined up for use in detector development, dosimetry studies and basic physics investigations such as ion beam fragmentation. The facility would work in the same way as particle physics experiments are carried out at CERN: researchers propose experiments, which are peer reviewed by a panel of experts who select suitable projects, and CERN controls the beam time allocation.

Before this can happen, however, LEIR needs some hardware modifications. These include a dedicated front-end that can accelerate many types of ion species, as well as a new extraction system and beamlines.

Design considerations

Looking in more detail at LEIR's required modifications, CERN researcher Adriano Garonna presented a status update on the ongoing design studies. He emphasized that LEIR will continue to be used as a lead ion accumulator for the LHC and other heavy ion experiments. The challenge, therefore, is to redesign LEIR for biomedical experiments, using the simplest and most cost-effective configuration, but while maintaining its current operational performance for the LHC.

Firstly, Garonna told the ICTR-PHE delegates, the current front-end is tailored for use with heavy ion sources and requires at least three weeks to swap between heavy and light ions. What's needed is a dedicated front-end, comprising a light ion source and a radiofrequency quadrupole (RFQ) optimized for light ions, that will offer fast switching between species. The beams will be injected into and accelerated in LEIR up to a kinetic energy of 440 MeV/u for carbon ions.

Garonna and colleagues have identified a suitable commercial light ion source (the Supernanogan Electron Cyclotron Resonance source) that can provide hydrogen, helium, carbon, nitrogen, oxygen and neon ions. Experiments are also ongoing to extract boron and lithium beams from this source, while the RFQ design is still in progress.

The next task is modification of the extraction system, which is currently designed to transfer high-brightness, 200 ns pulses to the Proton Synchrotron. Here, the goal is to create a dedicated resonant extraction system that delivers long spills (1–10 s) with uniform intensity for biomedical experiments. Such a slow extraction scheme could be implemented using minimal new hardware, explained Garonna, by installing an electrostatic septum and two magnetic septa. The CERN team has also demonstrated the feasibility of two potential resonance driving mechanisms: quadrupole driven extraction, which is easy to implement; and RF knock-out, which delivers better beam quality but requires installation of new hardware.

Finally, Garonna detailed a first proposal for two experimental beamlines for LEIR: a horizontal beamline running at up to the maximum energy (440 MeV/u) and a vertical beamline with a reduced energy of up to 75 MeV/u. Both are designed to provide pencil beams (5–10 mm) and broad beams (5 x 5 cm) and can be implemented using a total of four bending magnets and 12 quadrupoles.

The adjacent hall next to the ring will also need to be fitted out as an experimental area suitable for various biomedical experiments. The total cost of the infrastructure developments will likely come in at around €15 million. And while CERN has provided seed funding for this project, the majority of the money needs to be sourced from elsewhere.

So when can we expect to see the BioLEIR facility opening its doors to the international research community? Myers predicts that the full funding should be sourced during this year. Once this is achieved, the site could be up and running roughly two years later.

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