Increased glucose metabolism is characteristic for solid tumors. Thereby, glucose is important for the generation of ATP, supply of anabolic substrates and defense against reactive oxygen species in tumor cells. In preclinical models, restricting glucose availability using a ketogenic diet, calorie-restriction or transient fasting inhibits tumor growth.

Therefore, the purpose of the study is to evaluate whether a calorie-restricted, ketogenic diet and transient fasting can enhance the efficacy of reirradiation in patients with recurrent glioblastoma.

Inclusion Criteria:

• age >= 18 years
• recurrence of a histologically confirmed glioblastoma or gliosarcoma
• at least 6 months after first surgery
• at least 6 months after first radiotherapy
• interdisciplinary recommendation for reirradiation
• karnofsky performance status >= 60, ECOG <= 2
• creatinine <= 2,0 mg/dl, urea <= 100 mg/dl
• ALAT, ASAT <= 7x upper normal limit

Exclusion Criteria:

• bowel obstruction, subileus
• insulin-dependent diabetes
• decompensated heart failure (NYHA > 2)
• myocardial infarction within the last 6 months, symptomatic atrial fibrillation
• severe acute infection
• malnutrition, cachexia
• other medical conditions that might increase the risk of the dietary intervention
• pregnancy
• uncontrolled thyroid function
• pancreatic insufficiency
• dementia or other clinically relevant alterations of the mental status which could impair the ability of the patient to apply to the diet or understand the informed consent of the study