Hadron therapy is a state-of-the-art radiotherapy technique that uses proton or ion beams to target tumoural cells, while sparing surrounding healthy tissues from unwanted radiation. To achieve best results, it requires complex systems, called gantries, that rotate around the patient, carrying magnets that guide the hadron beams precisely onto tumours. Unfortunately, these are usually massive and costly machines, which represent a limiting factor for the spreading of the treatment technique.

Drawing on its expertise in superconducting magnets, a team at CERN has developed a novel superconducting and lightweight gantry, GaToroid, which promises to be much more compact than current machines while being just as precise. Unlike traditional rotating gantries, GaToroid could deliver particle beams from different directions without requiring the patient or the magnets to be moved. It exploits compact superconducting coils, located at different angles around the patient, to create a steady-state toroidal magnetic field that can direct particle beams onto a tumour, from any direction, sparing the patient from any stray magnetic field.

The use of superconductors gives the GaToroid design its unique compactness, with a diameter of five metres and an estimated weight of approximately 12 tonnes for proton beams. This represents a substantial weight reduction compared to traditional gantries for proton applications, which can weigh up to 270 tonnes.

In 2023, the team constructed and tested a demonstrator magnet consisting of one coil for the proton version of GaToroid, scaled down to one-third of the real size. The goal of the demonstrator was to prove the mechanical resistance of the structure and to check the quality of the field. The superconductor of choice was niobium–titanium, the same material used for the cables of the LHC magnets. “The tests we ran with our GaToroid demonstrator were highly successful, showing excellent performance and demonstrating that this magnet technology is ready for this type of application,” says Luca Bottura, head of the project.

The team performed several tests on the magnet and collected precise measurements of the magnetic field profile. “The magnet generated a field that matched the expected one with an error of less than 1%, and it showed absolutely no signs of mechanical degradation following the powering tests,” explains Gianluca Vernassa, who performed the mechanical and electromagnetic calculations on the demonstrator magnet.

The team that has designed, built and tested the demonstrator coil for the GaToroid project, next to a scaled 1:3 version of it. (Image: M. Cavazza/CERN)

This innovative design has already garnered significant attention within the particle therapy community across Europe. Notably, PARTREC has expressed interest in collaborating with the team to explore how GaToroid could be adapted for FLASH therapy.

Unlike in traditional radiotherapy, where treatment doses are delivered sequentially from different directions with long pauses to adjust the rotating gantry, FLASH radiotherapy delivers the entire dose from all directions simultaneously within 100 milliseconds. While conventional rotating gantries cannot operate in this mode due to their inherent limitations, the GaToroid system, with its fixed structure and ability to deliver beams from multiple angles without mechanical adjustments, would be perfectly suited to this type of treatment. This makes GaToroid a potential enabling technology for the use of hadrons in FLASH radiotherapy, which has not been possible with existing systems.

Following the success of the demonstrator, several GaToroid designs tailored to FLASH therapy have been proposed by the team. These include a conceptual design for very high-energy electrons (VHEE) and a proton-based system for which a proposal has already been developed in collaboration with PARTREC. The team is actively working on these developments and expects new results in 2025.

For more information about GaToroid consult the Knowledge Transfer website.