Proton therapy treatments at PSI use an in-house built accelerator, a compact cyclotron, called COMET. It was especially developed for medical applications by the company ACCEL (now part of Varian Medical Systems) and brought into service in 2007. It delivers a beam energy of 250 MeV, which can be reduced when needed for patient treatments.
COMET cyclotron during installation
Thanks to a superconducting magnet the accelerator COMET is very compact, still offering a high reliability which guarantees an all-year-round availability of the proton beam.
A kicker magnet, situated at the exit of the cyclotron is used to turn the beam on and off quickly (safety function). Switching time takes 200 microseconds, from sending the therapy control system signal to the loss of beam at the treatment area. Reduction of the high frequency cyclotron, turning-off the ion source as well as several mechanical beam stoppers are used as additional disconnection elements.
A carbon wedge degrader being introduced into the beam path, serves as energy setting, if necessary. The entire beam line serves as a fine-tune setting from its beginning to the treatment area as its final destination (impulse band width of ± 1 %).