title: Significant tumor volume reduction of meningiomas after stereotactic radiotherapy: results of a prospective multicenter study.
abstract: OBJECTIVE
  Stereotactic radiosurgery (SRS) is well established in the treatment of cranial base meningiomas. Fractionated stereotactic radiotherapy (SRT) offers an additional treatment option. Data for radiological regression differ, ranging from 13 to 61%. Therefore, the aims of this prospective study were to quantitatively analyze tumor volume (TV) shrinkage and to calculate determining factors.
  
  
  METHODS
  Eighty-four patients were examined under equal conditions before and after SRT. Fat-saturated axial T1-weighted contrast-enhanced magnetic resonance imaging scans with 1- to 3-mm slice thickness were used. After image fusion, TV was drawn in each slice to analyze TV shrinkage three-dimensionally by the planning system.
  
  
  RESULTS
  Mean TV had shrunk by 33% at 24 months (P = 0.02) and by 36% at 36 months (P = 0.0007) after SRT. With regard to half-year intervals, TV reduction decreased continuously towards a steady state (P < 0.0001). Younger age (P = 0.001) and smaller TV (P = 0.01) are determining factors. There was no correlation between TV reduction, prescribed dose, histological classification, sex, or previous operations.
  
  
  CONCLUSIONS
  Meningiomas shrink significantly after SRT. TV shrinkage declines towards a steady state, which is not yet defined. Younger age and smaller TV are determining factors. Previous operations, sex, prescribed dose, or histological subtypes do not affect TV shrinkage. Eighteen to 24 months after irradiation, when symptoms are clinically stable, is the best time for the first magnetic resonance imaging scans evaluating tumor control and shrinkage.
authors.affiliation: Department of Radiation Oncology, Philipps University, Marburg, Germany. henzel@med.uni-marburg.de
authors.forename: Martin
authors.initials: M
authors.lastname: Henzel
authors.forename: Markus W
authors.initials: MW
authors.lastname: Gross
authors.forename: Klaus
authors.initials: K
authors.lastname: Hamm
authors.forename: Gunnar
authors.initials: G
authors.lastname: Surber
authors.forename: Gabriele
authors.initials: G
authors.lastname: Kleinert
authors.forename: Thomas
authors.initials: T
authors.lastname: Failing
authors.forename: Gerd
authors.initials: G
authors.lastname: Strassmann
authors.forename: Rita
authors.initials: R
authors.lastname: Engenhart-Cabillic
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D005858:Germany; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008577:Meningeal Neoplasms / Q000473:pathology* / Q000601:surgery*; D008579:Meningioma / Q000473:pathology* / Q000601:surgery*; D008875:Middle Aged; D011446:Prospective Studies; D016634:Radiosurgery / Q000379:methods*; D016896:Treatment Outcome