The purpose of the study is to evaluate the short- and long term toxicity of radiotherapy to patients with recurrent high-grade glioma who have previously received radiotherapy and to determine the best dose and treatment regimen. Positron emission tomography (PET) using an amino acid tracer, 18-fluoro-ethyltyrosine (18F-FET), is used for target delineation.The study examines, in four sequential treatment groups, the effect of dose, hypofractionation and treatment volume on toxicity. Upon completion of the phase I part, the study progresses to phase II where the best dose- and treatment regimen will be chosen for treatment.