Patterns Of Failure After Gamma Knife Radiosurgery In Meningiomas: A Review Of Six Years Of Experience In The St. Elisabeth Hospital, Tilburg, The Netherlands.

Keywords: meningioma, recurrent disease, gamma knife, outcome, radiosurgery

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     Gamma Knife® Radiosurgery (GKRS) is a well accepted treatment modality for patients with intracranial meningiomas. High local control rates have been reported for benign meningiomas. On the contrary, atypical and malignant meningiomas yield a higher risk of recurrence after GKRS .
     In order to define risk factors associated with failure after GKRS, we evaluated the meningioma patients treated in our center between June 2002 and March 2008.
     Between June 2002 and March 2008, 258 patients with 344 meningiomas were treated in our center.
     The mean tumor volume was 4, 3 cm3 (range 0,01-21,5 cm3). The mean prescribed dose was 13 Gy (range 10-18 Gy.) The mean dose given to 100% of the tumor volume was 11 Gy (range 8- 18 Gy). The mean period of follow up was 47 months (range 18-87 months). Based on the definite diagnosis of a meningioma, 2 groups were distinguished: Group A: 129 meningiomas in 118 patients with unknown histology. The diagnosis of meningioma was based on MRI characteristics. Group B: 140 patients with 215 meningiomas had undergone surgery prior to the first GKRS. Of these, 156 (72,6%) were benign (WHO grade 1), 53 (24,7%) were atypical (WHO grade 2) and 6 (2,7%) were malignant (WHO grade 3).
     Group A: In this group a local control of 97.7% was found, 3 tumors of 129 showed progression. This confirms a high local control rate and corresponds with the literature. Group B: Local progression was found in 25 tumors in 19 patients. Of these, 3 meningiomas were benign, 22 either atypical or malign, yielding specific local control rates of 98% and 63% respectively.
     This is a retrospective study.
     No histological verification is needed to treat benign meningiomas with GKRS when MRI criteria are respected. However, the percentage of growth control decreases if atypical or malignant meningiomas are included.
     Histology is the most important risk factor for a recurrence after GKRS. The data of the atypical and malignant meningiomas of group B will be discussed with emphasis on growth pattern, site of recurrence and relationship with dose and volume.


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