Radiation therapy is the medical use of ionizing radiation to treat cancer. In conventional radiation therapy, beams of X rays (high energy photons) are produced by accelerated electrons and then delivered to the patient to destroy tumour cells. Using crossing beams from many angles, radiation oncologists irradiate the tumour target while trying to spare the surrounding normal tissues. Inevitably some radiation dose is always deposited in the healthy tissues.
When the irradiating beams are made of charged particles (protons and other ions, such as carbon), radiation therapy is called hadrontherapy. The strength of hadrontherapy lies in the unique physical and radiobiological properties of these particles; they can penetrate the tissues with little diffusion and deposit the maximum energy just before stopping. This allows a precise definition of the specific region to be irradiated. The peaked shape of the hadron energy deposition is called Bragg peak and has become the symbol of hadrontherapy.
With the use of hadrons the tumour can be irradiated while the damage to healthy tissues is less than with X-rays. idea of using protons for cancer treatment was first proposed in 1946 by the physicist Robert Wilson, who later became the founder and first director of the Fermi National Accelerator Laboratory (Fermilab) near Chicago. The first patients were treated in the 1950s in nuclear physics research facilities by means of non-dedicated accelerators. Initially, the clinical applications were limited to few parts of the body, as accelerators were not powerful enough to allow protons to penetrate deep in the tissues.
These measurements are also interesting for other applications, like radioprotection in space. NASA and other space agencies have started since several years the study of the risk assessment for astronauts in view of long duration space missions, such for instance the travel to Mars. Beyond many important risks of other nature, both galactic cosmic rays and particles from the almost unpredictable Solar Particle Events have to be considered. The design and optimization of spacecraft shielding requires a detailed knowledge of fragmentation processes.