Paul Scherrer Institute extends its proton therapy facility PROSCAN by a third gantry. It is delivered by Varian Medical Systems (VMS) as part of a joint research project. Gantry 3 is equipped with a cone beam CT and allows 360 degrees of rotation while occupying a 10.5 m diameter.
The integration of a gantry into the existing PSI-system typically being designed for a complete Varian system is a challenging project, since also the certification is to be maintained. Especially the interfaces between the PROSCAN-control system and the one of Gantry 3 have been a major development. Gantry 3 is designed to deliver proton beam of up to 8 nA with an accuracy better than a mm, while having a high level of over-current protection. This comprises a new current monitoring unit, several levels of interlock controllers and a beam energy dependent intensity compensation concept. One challenge concerns the specified layer switching time of 200 ms, required to reduce the treatment time to enable for repainting. After technical commissioning, acceptance tests and hand over, the clinical commissioning is foreseen in the second half of 2016 with the first patient treatment in December 2016.