title: Predictors of response to Gamma Knife radiosurgery for intracranial meningiomas.
abstract: OBJECTIVE
  In this paper, the authors' aim was to determine short-term volumetric and diametric tumor growth and identify clinical, radiological, and dosimetric predictors of adverse radiation events (AREs) following stereotactic radiosurgery (SRS) for intracranial WHO Grade I meningiomas.
  
  
  METHODS
  This is a retrospective review of all WHO Grade I meningiomas that were treated with SRS (primary or adjuvant) between December 2005 and June 2012 at the University Health Network. Seventy-five patients had at least 24 months of both clinical and radiological follow-up and were, therefore, included in this study. Tumor growth was defined as any volumetric or diametric change greater than 10% per year. Any variation less than +10% was considered growth stability. Volumetric measurements were made using T1-weighted gadolinium-enhanced 3-T MRI scans and ITK-SNAP software. Tumor growth rates were calculated using the specific growth rate (SGR). Univariate statistics were used to identify predictors of post-SRS AREs. All statistical analyses were performed using IBM SPSS.
  
  
  RESULTS
  Women accounted for 69.3% of patients, and the mean treatment age was 58.6 years. Median follow-up was 36.2 months. Twenty-one (28%) patients had undergone prior resection. Two (3%) patients required salvage surgical intervention following SRS. The majority of the lesions (56%) were skull base tumors. Median tumor volume and diameter were 5.2 cm3 and 27.5 mm, respectively. The absence of tumor growth was observed in 39 cases (52%) based on the volumetric measurements, while the absence of tumor growth was observed in 69 cases (92%) based on the diametric measurements. Twenty-six patients (34.6%) experienced new-onset AREs, including headache (17.3%), cranial neuropathy (10.6%), speech impairment (2.7%), tremors (2.7%), and ataxia (1.3%). Fourteen patients (18.7%) experienced new-onset edema, and 4 of these patients were symptomatic. A lower conformity index (1.24 vs 1.4) was significantly associated with the development of edema (p<0.001 power>0.8). Patients with meningiomas that had growth rates of more than 10% per year were more likely to experience long-term headaches after SRS (p=0.022).
  
  
  CONCLUSIONS
  Volume-based reporting of SRS outcomes for meningiomas may be a more accurate method given the complex morphology of some lesions. The conformity index was identified as a predictor of edema following radiosurgery.
authors.affiliation: Division of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto;
authors.forename: Alireza
authors.initials: A
authors.lastname: Mansouri
authors.affiliation: Division of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto;
authors.forename: Soroush
authors.initials: S
authors.lastname: Larjani
authors.affiliation: Division of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto;|Division of Neurosurgery, University of Toronto;
authors.forename: George
authors.initials: G
authors.lastname: Klironomos
authors.affiliation: Department of Radiation Oncology, Princess Margaret Cancer Centre/University Health Network, University of Toronto;
authors.forename: Normand
authors.initials: N
authors.lastname: Laperriere
authors.affiliation: Division of Neurosurgery, University of Toronto;|Keenan Research Centre, Li Ka Shing Knowledge Institute, St. Michael's Hospital, Toronto; and.
authors.forename: Michael
authors.initials: M
authors.lastname: Cusimano
authors.affiliation: Division of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto;|Division of Neurosurgery, University of Toronto;
authors.forename: Fred
authors.initials: F
authors.lastname: Gentili
authors.affiliation: Division of Neurosurgery, University of Toronto;|Department of Surgery (Neurosurgery), Sunnybrook Health Sciences Centre, University of Toronto, Ontario, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Schwartz
authors.affiliation: Division of Neurosurgery, Toronto Western Hospital, University Health Network, Toronto;|Division of Neurosurgery, University of Toronto;
authors.forename: Gelareh
authors.initials: G
authors.lastname: Zadeh
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016208:Databases, Factual; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008579:Meningioma / Q000473:pathology / Q000601:surgery*; D008875:Middle Aged; D011183:Postoperative Complications / Q000453:epidemiology / Q000628:therapy; D011379:Prognosis; D011446:Prospective Studies; D011829:Radiation Dosage; D016634:Radiosurgery / Q000009:adverse effects / Q000379:methods*; D012189:Retrospective Studies; D016896:Treatment Outcome; D055815:Young Adult
keywords: ARE = adverse radiation event; CI RTOG = Radiation Therapy Oncology Group Conformity Index; RT = radiotherapy; SGR = specific growth rate; SRS = stereotactic radiosurgery; TVR = treatment volume ratio; adverse event; meningioma; predictor; stereotactic radiosurgery