Hadrontherapy is the youngest generation of conventional radiotherapy, which is carried out with X-rays (called gammas or photons by the physicists).
Hadrontherapy makes use of beams of protons (hydrogen ions), of carbon ions and of neutrons, which are all heavier than the electrons and are called hadrons.
Protons accelerated up to 200 MeV, and carbon ions accelerated up to 4'700 MeV, allow the irradiation of deep-seated tumours, following their contours with millimetric precision and thus sparing the surrounding healthy tissues.
The production of protons and carbon ions at these energies is more difficult and costly than the production of 10 or 20 MeV electrons required for conventional therapy with X-rays.
Only protons of 200 MeV can in fact penetrate up to 27 cm in the body and thus reach deep-seated tumours. In order to penetrate at the same depth, carbon ions must be accelerated to an energy about twentyfour times greater (4'700 MeV), which implies the use of even larger accelerators.