A PERFORMANCE STUDY OF THE LOMA-LINDA PROTON MEDICAL ACCELERATOR

More than three years have passed since Loma Linda treated the first c ancer patient with the world's first proton accelerator dedicated to r adiation therapy. Since that time, over 1000 patients have completed t reatments and the facility currently treats more than 45 patients per day. With a typical intensity of 3 X 10(10) protons per pulse and 27 p ulses per minute, dose rates of 90-100 cGy/min are easily achieved on a 20-cm diameter field. In most cases, patient treatment times are 2 m in, much less than the patient alignment time required before each tre atment. Nevertheless, there is considerable medical interest in increa sing field sizes up to 40-cm diameter while keeping dose rates high an d treatment times low. In this article, beam measurements relevant to intensity studies are presented and possible accelerator modifications for upgrades are proposed. It is shown that nearly all intensity loss es can be ascribed to the large momentum spread of the injected beam a nd occur at or near the injection energy of 2 MeV. The agreement betwe en calculations and measurements appears quite good. In addition, opti mum beam characteristics for a new injector are discussed based upon t he momentum acceptance and space charge limits of the Loma Linda synch rotron.