P13.16 * COMPLICATIONS AFTER GAMMA KNIFE RADIOSURGERY FOR BRAIN TUMORS LOCATING ADJACENT THE BRAINSTEM

Abstract

OBJECTIVE: Gamma Knife Radiosurgery (GKRS) is still challenging for the tumors locating adjacent brainstem because of dose limitation to brainstem, and the 12-Gy volume of brainstem has been reported as an important factor for development of radiation-induced complications. We aimed to investigate the incidence and relevant factors of complications after GKRS, whilewetry to minimize the 12-Gy volume of brainstem.METHODS:Weretrospectively reviewed clinical, radiological and dosimetry data of 76 patients who underwent GKRS for brain tumors locating adjacent the brainstem. The most common diagnosis was vestibular schwannoma (n = 41), followed by meningioma (n = 21), metastatic brain tumor (n = 13), and ependymoma (n =1). The mean target volume was 3.7 cc (range, 0.211-12.2) at the time of GKRS, and the mean prescription dose was 12.7 Gy (range 8-20). The mean 12-Gy volume was 0.029 cc (range, 0.002-0.2). The location of tumors was intra-axial in 10 (13.2%) and extra-axial in 66 (86.8%). The 12-Gy volume of brainstem was calculated by intersecting the volume within brainstem from the prescription dose. The signal change of brainstem was defined as signal alteration on T2 or T1-weighted MRI after GKRS. RESULTS: The median clinical follow-up duration was 31.5 + 14.3 months (range, 0.9-63.6). Among 76 lesions, the signal change of brainstem was observed in 7 (9.2%) with a median interval of 5.5 + 4.08 months (range, 0.5-12) to development. Three tumors showing the signal change of brainstem were symptomatic, however successfully managed with oral steroid administration. Among various factors, only radiation-induced intratumoral necrosis (RIN) was a significant factor for the development of signal change of brainstem (p = 0.027). RIN was observed in 39 (51.3%) tumors with the median onset time of 5.4 + 0.9 months after GKRS. The actuarial local tumor control rates at 1, 2 and 3 years after GKRS were 93.7%, 77.7% and 52.8%, respectively. CONCLUSIONS: In our series, the radiation-induced signal change of brainstem was observed in 9.2% after GKRS with an effort to minimize the 12-Gy volume of brainstem and only RIN was a significant relevant factor. Therefore, we suggest that close observation should be required to monitor radiation-induced brainstem injury when RIN is developed in the follow-up imaging after GKRS.