CLIC lights the way for FLASH therapy

10 November 2020
High-gradient accelerating structure

Technology developed for the proposed Compact Linear Collider (CLIC) at CERN is poised to make a novel cancer radio‑therapy facility a reality. Building on recently revived research from the 1970s, oncologists believe that ultrafast bursts of electrons damage tumours more than healthy tissue. This “FLASH effect” could be realised by using high-gradient accelerator technology from CLIC to create a new facility at Switzerland’s Lausanne University Hospital (CHUV).

Traditional radiotherapy scans photon beams from multiple angles to focus a radiation dose on tumours inside the body. More recently, hadron therapy has offered a further treatment modality: by tuning the energy of a beam of protons or ions so that they stop in the tumour, the particles deposit most of the radiation dose there (the so-called Bragg peak), while sparing the surrounding healthy tissue by comparison. Both of these treatments deliver small doses of radiation to a patient over an extended period, whereas FLASH radiotherapy is thought to require a maximum of three doses, all lasting less than 100 ms.

Look again

When the FLASH effect was first studied in the 1970s, it was assumed that all tissues suffer less damage when a dose is ultrafast, regardless of whether they are healthy or tumorous. In 2014, however, CHUV researchers published a study in which 200 mice were given a single dose of 4.5 MeV gamma rays at a conventional therapy dose-rate, while others were given an equivalent dose at the much faster FLASH-therapy rate. The results showed explicitly that while the normal tissue was damaged significantly less by the ultrafast bursts, the damage to the tumour stayed consistent for both therapies. In 2019, CHUV applied the first FLASH treatment to a cancer patient, finding similarly positive results: a 3.5 cm diameter skin tumour completely disappeared using electrons from a 5.6 MeV linear accelerator, “with nearly no side effects”. The challenge was to reach deeper tumours.

Now, using high-gradient “X-band” radio-frequency cavity technology developed for CLIC, CHUV has teamed up with CERN to develop a facility that can produce electron beams with energies around 100 MeV, in order to reach tumour depths of up to 20 cm. The idea came about three years ago when it was realised that CLIC technology was almost a perfect match for what CHUV were looking for: a high-powered accelerator, which uses X-band technology to accelerate particles over a short distance, has a high luminosity, and utilises a high current that allows a higher volume of tumour to be targeted.

“CLIC has the ability to accelerate a large amount of charge to get enough luminosity for physics studies,” explains Walter Wuensch of CERN, who heads the FLASH project at CERN. “People tend to focus on the accelerating gradient, but as important, or arguably more important, is the ability to control high-current, low-emittance beams.”

It really looks like it has the potential to be an important complement to existing radiation therapies

The first phase of the collaboration is nearing completion, with a conceptual design report, funded by CHUV, being created together by CERN and CHUV. The development and construction of the first facility, which would be housed at CHUV, is predicted to cost around €25 million, and CHUV aims to complete the facility within three years.

“The intention of CERN and the team is to be heavily involved in the process of getting the facility built and operating,” states Wuensch. “It really looks like it has the potential to be an important complement to existing radiation therapies.”

Cancer therapies have taken advantage of particle accelerators for many decades, with proton radiotherapy entering the scene in the 1990s. The CERN-based Proton-Ion Medical Machine Study, spawned by the TERA Foundation, resulted in the National Centre for Cancer Hadron Therapy (CNAO) in Italy and MedAustron in Austria, which have made significant progress in the field of proton and ion therapy. FLASH radiotherapy would add electrons to the growing modality of particle therapy.

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