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.