Radiation-induced intratumoral necrosis and peritumoral edema after Gamma knife radiosurgery for intracranial meningiomas

Keywords: meningioma, gamma knife, complications, radiation injury, outcome

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     . Meningioma radiosurgery can be associated with complications and radiation injury.
     Our purpose was to study the incidence and clinical significance of radiation-induced intratumoral necrosis (RIN) and peritumoral edema after Gamma knife radiosurgery (GKRS) for intracranial meningiomas, and to investigate relevant factors
     We retrospectively analyzed the data of sixty-seven patients with 74 intracranial meningiomas who underwent GKRS between August 2008 and January 2011. The mean age at the time of GKRS was 59.6 years (range, 29-90). The mean lesion volume was 4.6 cc (range, 0.3-20), and the mean prescription dose of 13.2 Gy (range, 11-18) was delivered to the mean 50.6 % (range, 45-70) isodose line.
      RIN was defined as newly developed intratumoral necrosis or enlargement of pre-existing necrosis after GKRS.
     RIN occurred in 22 (29.7 %) of 74 lesions during the median follow-up duration of 19.9 ± 1.0 months (range, 3.7–35.1). The median interval to RIN was 6.5 ± 0.4 months (range, 3.7–17.0). Among the 22 lesions, peritumoral edema was present in 8 (36.4%) at the time of GKRS. There was no significant change of tumor volume itself between the time of GKRS and RIN (mean; 7.0 vs. 7.8 cc). However, 14 (63.6 %) lesions showed peritumoral edema at the time of RIN and the peritumoral edema volume increased significantly (p=0.013, Wilcoxon signed ranks test). Ten out of 22 lesions were symptomatic and decompressive surgery was required in 1 patient because of severe peritumoral edema. Target volume >4.5 cc (p=0.002) was a significant factor related to RIN, and development of RIN (p=0.001) and maximum dose >24 Gy (p=0.017) were significantly related to development or aggravation of peritumoral edema.
     This was a retrospective review.
     According to our results, we suggest that close observation is required for meningiomas of >4.5 cc showing RIN after GKRS .
     Larger volumes can be associated with accompanying peritumoral edema which may worsen the  neurological condition when they are located adjacent to critical structures or the cerebrospinal fluid pathway


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