title: Gamma Knife radiosurgery for skull base meningioma: long-term results of low-dose treatment.
abstract: OBJECTIVE
  In this study, the authors evaluate the long-term results after Gamma Knife radiosurgery of cranial base meningiomas. This study is a follow-up to their previously published report on the early results.
  
  
  METHODS
  Between January 1994 and December 2001, the authors treated benign cranial base meningiomas in 108 patients using low-dose Gamma Knife radiosurgery. The tumor volumes ranged from 1.7 to 55.3 cm3 (median 8.1 cm3), and the radiosurgery doses ranged from 8 to 12 Gy (median 12 Gy) to the tumor margin.
  
  
  RESULTS
  The mean duration of follow-up was 86.1 months (range 20-144 months). Tumor volume decreased in 50 patients (46%), remained stable in 51 patients (47%), and increased (local failure) in 7 patients (6%). Eleven patients experienced tumor recurrence outside the treatment field. Among these patients, marginal failure was seen in 5 and distant recurrence was seen in 6. Seven patients were thought to have malignant transformation based on histological or radiological characteristics of the lesion. The actuarial progression-free survival rate, including malignant transformation and outside recurrence, was 93% at 5 years and 83% at 10 years. Neurological status improved in 16 patients (15%). Permanent radiation injury occurred in 7 patients (6%).
  
  
  CONCLUSIONS
  Gamma Knife radiosurgery is a safe and effective treatment for cranial base meningiomas as demonstrated with a long-term follow-up period of > 7 years. Surgeons must be aware of the possibility of treatment failure, defined as local failure, marginal failure, and malignant transformation; however, this may be the natural course of meningiomas and not related to radiosurgery.
authors.affiliation: Department of Neurosurgery, Osaka City General Hospital, Osaka, Japan. y-iwai@rc5.so-net.ne.jp
authors.forename: Yoshiyasu
authors.initials: Y
authors.lastname: Iwai
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Yamanaka
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Ikeda
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D053208:Kaplan-Meier Estimate; D008279:Magnetic Resonance Imaging; D008297:Male; D008579:Meningioma / Q000473:pathology / Q000601:surgery*; D008875:Middle Aged; D009364:Neoplasm Recurrence, Local; D016634:Radiosurgery / Q000009:adverse effects / Q000379:methods*; D019292:Skull Base Neoplasms / Q000473:pathology / Q000601:surgery*; D016896:Treatment Outcome; D055815:Young Adult