Radiotherapy is a long-standing treatment method which makes use of ionising radiation for the treatment of patients with malignancies. Radiotherapy is currently undergoing major evolvements. The treatment method has gone from being imprecise and was often accompanied by unpreventable side effects to a high-precision therapy which can compete with surgery and other focal curative and less toxic treatment strategies. Through the improved quality of imaging and the availability of new techniques, it became possible to use both anatomical and functional information to accurately determine the position and characteristics of the tumour in space and time. Imaging is also used to enhance the guidance of x-rays during the actual treatment. This enables the reduction of radiotherapy margins and a decrease in the radiation dose aimed at normal tissues.- For many indications, therefore, the delivery of the complete radiation dose can be reduced to only a few fractions, which is not only very effective, but is especially beneficial for the patient.