Significance of Tumor Volume Related to Peritumoral Edema in Intracranial Meningioma Treated with Extreme Hypofractionated Stereotactic Radiation Therapy in Three to Five Fractions

Background: To investigate the treatment results of intracranial meningiomas treated with hypofractionated stereotactic radiation therapy in three to five fractions. Methods: Thirty-one patients (32 lesions) with intracranial meningioma were treated with hypofractionated stereotactic radiation therapy in three to five fractions using CyberKnife. Fifteen lesions were diagnosed as Grade I (World Health Organization classification) by surgical resection and 17 lesions were diagnosed as meningioma based on radiological findings. The median follow-up time was 48 months. The median planning target volume was 6.3 cm(3) (range, 1.4-27.1), and the prescribed dose (D90 <=) ranged from 21 to 36 Gy (median, 27.8) administrated in three to five fractions. Results: Five-year overall and progression-free survival rate of all 31 patients with intracranial meningioma was 86 and 83%, respectively. Five-year progression-free rate of all 32 lesions was 87%. Six of the 31 patients (19%) developed marked peritumoral edema, three of whom were asymptomatic and three symptomatic, the latter with late adverse effects of more than or equal to Grade 3. The mean planning target volume of the six lesions with marked peritumoral edema was 15.6 cm(3), and for the remaining 26 lesions without marked peritumoral edema was 7.1 cm(3) (P = 0.004). The threshold diameter of 2.56 cm for meningioma was calculated from the planning target volume (11 cm(3)) and was used as marker of developing peritumoral edema (P = 0.003). Conclusions: Tumor volume is a significant indicative factor for peritumoral edema in intracranial meningioma treated with hypofractionated stereotactic radiation therapy in three to five factions.