Tumours of the central nervous system are a very inhomogeneous group of malignant tumours. Their diversity is mainly the result of the wide variety of different tissues and structures present in the central nervous system from which they can develop. Due to the low radiation sensitivity of the central nervous system, relatively high and thereby effective doses of irradiation can be applied with very good subjective and objective tolerance. The target volume can include the entire neurocranium with spinal cord (medulloblastoma), or have a diameter of just a few millimetres (metastases). Radiotherapy is used particularly when the tumour is extensive and/or surgery is not an option. Tumours can be irradiated pre-operatively (neoadjuvant therapy) to reduce the size of the tumour and make it possible for surgery to take place.