Year Round Proton Radiation Therapy At PSI Using A New, Dedicated Cyclotron

A new proton accelerator, a superconducting cyclotron, has been put into operation for patient treatment. The accelerator is used in conjunction with a gantry, a device which delivers the protons to the patient from any angle. The desired dose distribution is achieved by scanning a small pencil beam of protons throughout the tumor. The performance of the new accelerator has been excellent since the start of medical operation.

Proton radiation therapy for deep seated tumors using a compact gantry with spot scanning technology was PSI’s unique contribution to particle radiotherapy worldwide. After 10 years of medical operation (over 260 patients were treated between 1996 and 2005) with PSI’s main accelerator as the beam source, we installed a dedicated proton accelerator for medical use. This relieved the medical program from yearly technical accelerator shut downs of several months and from limited beam availability per day and week, all of which were due to the complexity of a large research facility.

The dedicated proton accelerator (called the COMET) is a compact, superconducting 250 MeV cyclotron. The original design came from the National Superconducting Cyclotron Laboratory at Michigan State University and was adapted to PSI’s specifications and requirements. They included reliable all year round beam production for clinical operation of both the original gantry (Gantry 1) and the eye treatment facility as well as technical flexibilities to accommodate the next generation gantry which features advanced beam scanning and is presently under construction (Gantry 2). Gantry 2 is a further PSI development which will bring beam scanning to the forefront of the medical use of protons.

The cyclotron was fabricated by ACCEL Instruments GmbH (Varian) in Bergisch Gladbach, Germany, and was successfully installed, commissioned and connected to Gantry 1 in 2006/7. The collaboration between ACCEL and PSI resulted in a system that meets stringent specifications, including reliability and efficient maintenance. The technical performance of the cyclotron has met all expectations and the first patient was treated with Gantry 1 and COMET in February 2007. After a planned shut down for technical fine tuning between June and early August patient treatments have been resumed. Future medical operation will be year round.

Gantry 2, with advanced beam scanning and features allowing the treatment of moving targets, will be commissioned in 2008. It is anticipated that the sophisticated technology of COMET and Gantry 2 will determine the future state-of-the-art of proton radiation therapy. Technology transfer to industry and clinics who are interested in advanced proton therapy facilities is foreseen.