Inclusion Criteria:

- histologically confirmed atypical meningioma

- macroscopic tumor after biopsy or subtotal resection

- Simpson Grade 4 or 5

- prior photon radiotherapy to the clinical target volume (CTV) of 48-52 Gy

- beginning of study treatment no later than 12 weeks after surgery

- age ≥ 18 years of age

- Karnofsky Performance Score ≥ 60

- For women with childbearing potential, adequate contraception

- Ability of subject to understand character and individual consequences of the
clinical trial

- Written informed consent (must be available before enrolment in the trial)

Exclusion Criteria:

- refusal of the patients to take part in the study

- previous radiotherapy of the brain

- optic nerve sheath meningioma (ONSM)

- time interval of > 12 weeks after primary diagnosis (neurosurgical intervention) and
beginning of study treatment

- Patients who have not yet recovered from acute toxicities of prior therapies

- Known carcinoma < 5 years ago (excluding Carcinoma in situ of the cervix, basal cell
carcinoma, squamous cell carcinoma of the skin) requiring immediate treatment
interfering with study therapy

- Pregnant or lactating women

- Participation in another clinical study or observation period of competing trials,
respectively