This is a multi-institutional phase III clinical study of interventional type. The trial will include 220 patients with confirmed unifocal glioblastoma over a period of 3 years + 3 years of follow up.

Patients with unifocal glioblastoma (diagnosis confirmed by histology on tumoral biopsy or surgical specimen) and who meet all eligibility criteria will be randomized in one chemoradiotherapy arm :

• Conventional arm: 3-dimensional conformational radiotherapy + Temozolomide
• Experimental arm : simultaneous-integrated boost with intensity-modulated radiotherapy guided by magnetic resonance spectroscopic imaging + Temozolomide The patient monitoring will be regular and standardized. The main objective of this study is to improve overall survival of patients treated in experimental group (with simultaneous integrated boost).

Inclusion Criteria:

1. Patients must have unifocal glioblastoma (grade IV astrocytoma, WHO classification). The GBM can be:

   • Or resectable and the patient has received curative surgery
   • Or unresectable, and the largest tumor diameter (contrast enhancement) must be less than 5 cm on MRI

2. In all cases, the diagnosis must be confirmed by a pathologist. In patients for whom surgery is not possible, the diagnosis is confirmed by a biopsy of tumor tissue.

3. Methylation status of MGMT gene promoter is known

4. Patients who have undergone resection should have received an MRI or a scan after surgery in order to visualize residual tumor. If not, the operative report must be available.

5. Surgery or biopsy must have occurred 45 days before the start of radiotherapy.

6. WHO ≤ 2

7. Age ≥ 18 years

8. Signed Consent collected before any specific procedure in the study

9. Patient member in a national insurance scheme

Exclusion Criteria:

1. Signs of hemorrhage on pre-radiotherapy MRI preventing a good spectrometric analysis

2. Patient with multifocal glioblastoma

3. Tumor located within 2 cm of the optic chiasm

4. Patient with leptomeningeal metastases,

5. patients prone to epileptic seizures despite treatment with anticonvulsant

6. Patients who received other previous treatment for glioblastoma multiforme

7. Abnormal haematological results at inclusion with:

   • Neutrophils < 1500/mm3
   • Blood-platelets < 100000/mm3

8. Severe or chronic renal insufficiency (creatinin clearance ≤ 30 ml/min calculated using Cockroft-Gault's formula

9. Patient unable to follow procedures, visits, examinations described in the study

10. Any usual formal indication against imaging examinations (important claustrophobia, pace maker ...)

11. Pregnant women or nursing mothers can not participate in the study. Women of childbearing age must have a negative pregnancy test within 72 hours prior to study entry

12. Men and women of childbearing age must use effective contraception at study entry and throughout the study

13. Any concomitant or previous malignant disease within 5 years prior to study entry

14. Any prior systemic chemotherapy within 5 years prior to inclusion (for malignant disease in medical history)

15. Any other medical conditions making the inclusion of the patient in the study inappropriate in the opinion of the investigator

16. Patient under legal guardianship