Clinical Technology

A comprehensive white paper on technology trends explains how and why proton therapy is gaining increasing importance as a cancer treatment option. Part one covers how compact solutions are making proton therapy more accessible worldwide, as smaller generally equals cheaper. The invention and integration of superconducting magnets allowed for the production of a compact, affordable proton therapy solution.

Traditionally, proton therapy centers have been large facilities, featuring three to five treatment rooms in order to optimize the return on investment. However, with the benefits of proton therapy not yet profoundly anchored in general medical practice, patient recruitment proved to be challenging in some cases. Requiring a considerable structure and investment, these multi-room centers were also unattainable for smaller hospitals that wanted to include proton therapy in their cancer treatment options. Manufacturers therefore sought and found a more compact solution in one-room systems.


The major obstacle is the amount of energy needed to accelerate protons, which are about 2,000 times heavier than electrons used to make photons, resulting in a much higher magnetic rigidity. Typically 6 MeV electrons from a linear accelerator, or linac, suffice to make photons which can go through the body. Such a linac is a relatively cheap piece of equipment, whereas reaching a 32-centimeter depth in the body with protons requires 230 MeV. To obtain this amount of energy you need much bigger magnets to bend the beam. An important characteristic of a beam of particles is the magnetic rigidity – the product of the field times the radius of curvature of the magnet – which is a constant for a given energy. For 230 MeV protons the magnetic rigidity is 2.3 tesla-meter, which means that if you use a field of 1T – an average industrial field – you get a radius of curvature of 2.3 meters. However, superconducting magnets can push the magnetic field up to 4.6T, bringing the radius of curvature down to 50 centimeters. Yet you need extreme cryogenics to achieve the necessary 4 K temperature to cool these magnets down, which in turn increases materials costs.

Scale down

“Even if proton therapy may not become available at the same price as photon therapy in the near future, superconducting magnets – together with smaller, less revolutionary adaptations – already allow us to offer proton therapy at half the price today, as size and costs are related,” states Yves Jongen. “Our original Cyclone®230 delivered 2T at extraction, the radius at which the beam came out of the machine being 1.1 meters and the radius of the cyclotron itself a little over 2 meters. This made the machine a total of 200 tons and 4.3 meters in diameter. Today we were able to reduce these measurements to 45 tons and 2.5 meters. This in turn makes transport and assemblage much simpler.”


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