Proton therapy accelerators-a survey

Many new proton therapy facilities began operation in the 1990´s, mostly in Europe and Japan. Protons of maximum energy around 250 MeV are delivered to the patient from an accelerator-a cyclotron or a synchrotron-via a fixed beam line or gantry. A future generation of proton therapy facilities will enable a continuous upgrade path to precision 3-D multi-field irradiation of cancerous tumors. The ultimate goal is to enable intensity modulation in beam delivery from many fields through an active scanning nozzle. This will result in ultra-low collateral radiation, compared to conventional X-ray therapy. Another goal is to fully exploit the imaging possibilities naturally provided by the use of 250 MeV protons. One imaging technique uses a gantry mounted PET camera for near real time dose verification, observing the decay of positron emitting isotopes created by nuclear collisions in a therapy session. A second technique uses new detector and software technologies to enable low dose in situ proton radiography, with millimeter resolution.