Initial experience of using an active beam delivery technique at PSI

At PSI a new proton therapy facility has been assembled and commissioned. T he major features of the facility are the spot scanning technique and the v ery compact gantry. The operation of the facility was started in 1997 and t he feasibility of the spot scanning technique has been demonstrated in prac tice with patient treatments. In this report we discuss the usual initial d ifficulties encountered in the commissioning of a new technology, the very positive preliminary experience with the system and the optimistic expectat ions for the future. The long range goal of this project is to parallel the recent developments regarding inverse planning for photons with a similar advanced technology optimized for a proton beam.