A challenge for high-precision radiation therapy: The case for hadrons

Developments in Hadron therapy, i.e., fast neutrons, protons; pious, heavy ions and boron neutron capture therapy are reviewed. For each type of parti cle, operational and closed facilities are listed as well as planned new fa cilities. Improvements in clinical results have always been linked to technological d evelopments and better physical selectivity of the irradiation. Exploring t he benefit of further improvement in dose localization expected from proton s and conformal therapy is the challenge for the coming years. The radiobiological rationale for high-LET radiation in cancer treatment, p roposed in the fifties, is still valid and has not been contradicted by rec ent radiobiological findings. This justifies the planning of a therapy facility where protons and heavy i ons (carbon ions) could be applied, under optimal physical and technical co nditions. Appropriate selection between low- and high-LET radiation for a particular tumor is indeed a radiobiological problem, independent of technical develop ment.