Radiotherapy is one of the most common and effective therapy for cancer. Generally, patients are treated with X-rays produced at electron accelerators. The use of high-energy charged particles was proposed several years ago, both for their physical and radiobiological advantages compared to X-rays. Particle therapy is now becoming an emerging technique in radiotherapy. Protons and carbon ions have been used for treating many different solid cancers, and several new centers with large accelerators are under constructions. However, there is currently an open debate on the cost/benefit ratio of this technique. The Biophysics group at GSI had in the past years an intense activity in the 12C-ion therapy pilot project. The treatment of tumours at the base of the skull and brain was extremely successfully, using the technique of raster scanning (see figure). The therapy project paved the way to hadrontherapy in Europe, leading to the construction and planning of several clinical accelerator facilities. This talk considers the present clinical results in the field, and identifies the open research questions.