The great advantage of Proton Therapy is the lower dose to the healthy tissue resulting in reduced collateral damage. The treatment causes only minimal side effects or no acute side effects at all. As a consequence, a gradual escalation of the dose to the tumour can be practised – typically in the frame of clinical trials. More radical treatment with better tumour control is possible, higher cure rates are achievable. With this kind of almost side effect free radiation therapy, many tumour entities can be treated with higher expectation of cure. Especially for children undergoing cancer treatment it is very important that their quality of life can be preserved.