Neurosurgery 2012-03
Risk factors for posttreatment edema in patients treated with stereotactic radiosurgery for meningiomas.   
Peritumoral edema is a recognized complication following stereotactic radiosurgery (SRS).
To evaluate the risk of posttreatment peritumoral edema following SRS for intracranial meningiomas and determine predictive factors.
Between 2002 and 2008, 173 evaluable patients underwent CyberKnife or Gamma Knife SRS for meningiomas. Eighty-four patients (49%) had prior surgical resections, 13 patients had World Health Organization grade II (atypical) meningiomas, and 117 patients had a neurological deficit before SRS. Sixty-two tumors were in parasagittal, parafalcine, and convexity locations. The median tumor volume was 4.7 mL (range, 0.1-231.8 mL). The median prescribed dose and median prescribed biologically equivalent dose were 15 Gy (range, 9-40 Gy) and 67 Gy (range, 14-116 Gy), respectively. Ninety-seven patients were treated with single-fraction SRS, 74 received 2 to 5 fractions, and 2 received >5 fractions.
The median follow-up was 21.0 months. Thirteen patients (8%) developed symptomatic peritumoral edema, with a median onset time of 4.5 months (range, 0.2-9.5 months). The 3-, 6-, 12-, and 24-month actuarial symptomatic edema rates were 2.9%, 4.9%, 7.7%, and 8.5%, respectively. The crude tumor control rate was 94%. On univariate analysis, large tumor volume (P = .01) and single-fraction SRS (P = .04) were predictive for development of posttreatment edema.
SRS meningioma treatment demonstrated a low incidence of toxicity; however, large tumor volumes and single-fraction SRS treatment had an increased risk for posttreatment edema. Risk factors for edema should be considered in meningiomas treatment.

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