In 1996, an irradiation unit (Gantry 1) was equipped for the first time to use the so-called spot-scanning proton technique developed at PSI. With this technique, tumours deep inside the body are scanned three-dimensionally with a proton beam about 5 to 7 mm in width. By superimposing many individual proton spots – about 10,000 spots per litre volume – the tumour is evenly exposed to the necessary radiation dose, which is monitored individually for each spot. This allows an extremely precise, homogeneous irradiation that is optimally adapted to the usually irregular shape of the tumour. The technique enables as much as possible of the surrounding healthy tissue to be spared. The first gantry was in operation for patients from 1996 to the end of 2018. In 2013, the second Gantry 2, developed at PSI, went into operation, and in mid-2018 another treatment station, Gantry 3, was opened.