TTFields and Radiosurgery of Recurrent Glioblastoma +/- 18F-Fluoro-Ethyl-Thyrosine

Inclusion Criteria: 1. Patient's written informed consent (IC) obtained at the latest the day after planning MRI; 2. Legal capacity: patient can understand the nature, significance, and consequences of the study; 3. Age ≥18 years (no upper age limit); 4. Karnofsky Performance Score (KPS) ≥ 70; 5. Recurrence of GBM (WHO grade IV) based on RANO criteria or GBM after subtotal resection of recurrence with macroscopic residual tumor; 6. Histological confirmation of GBM at initial or secondary diagnosis; 7. Previous radiotherapy of glioma with a total dose of 59.4 - 60 Gy (single dose 1.8 - 2.0 Gy) and chemotherapy with temozolomide; 8. At least 6 months between the end of the first course of radiotherapy and radiosurgery; 9. Recurrent tumor visible on FET-PET and/or T1Gd-MRI, with the maximum diameter up to 5 cm by either technique (in case of multifocal tumors, the sum of all diameters must be 5 cm on FET-PET and T1Gd-MRI); 10. Start of TTFields before radiosurgery; 11. Disease free from other cancers for ≥ 5 years; 12. Adequate haematologic, renal and hepatic function (absolute neutrophil count ⩾1000/mm3; haemoglobin ⩾100 g/L platelet count, ⩾100,000/mm3; serum creatinine level ⩽1.7 mg/dL (\<150 μmol/L); total serum bilirubin level ⩽ the upper limit of normal and liver-function values, \<3 times the upper limit of normal); Exclusion Criteria: 1. Recent (≤ 4 weeks before IC) histological result showing no tumor recurrence; 2. Previous treatment of GBM with bevacizumab; 3. Chemotherapy or molecular targeted therapies planned before diagnosis of further tumor progression after study intervention 4. Simultaneous participation in other interventional trials which could interfere with this trial and/or participation in a clinical trial within the last thirty days before the start of this study and/or previous participation (randomization) in this study; 5. Pregnancy, nursing, or patient not willing to prevent a pregnancy during treatment; 6. Known or persistent abuse of medication, drugs or alcohol; 7. Known allergy against the MRI contrast agent gadolinium or the PET tracer 18F-FET or against any of the components; 8. Evidence of increased intracranial pressure (midline shift \>5 mm, clinically significant papilledema, vomiting and nausea or reduced level of consciousness); 9. Implanted pacemaker, programmable shunts, defibrillator, deep brain stimulator, other implanted electronic devices in the brain, or documented clinically significant arrhythmias. 10. Gross total resection of recurrence confirmed with postoperative MRI and negative FET-PET result 11. Other malignancies ,except for non-melanomatous skin cancers, or carcinoma in-situ of uterus, cervix or bladder