ESTRO 2021 Abstract Book

S877

ESTRO 2021

RT dose was 60Gy (50 - 65Gy). 21 (40%) patients underwent a repeat maximal safe resection, while 4 (7.5%) patients underwent only biopsy. The median time interval from initial RT to ReRT was 34.8 months (4.4 - 187) and mean ReRT EQD2 3 was 45.4Gy. On the basis of dose per fraction, 25 patients (47%) received Conventional RT (1.8-2Gy), 5 (9.5%) got moderately hypofractionated RT (2 - 4Gy /#) and 23 (43%) patients received ultra - hypofractionated RT (> 4Gy/ #). The median PTV at reirradiation was 153.8 cc (4.5-582). The median BED 3 at ReRT was 76.2Gy (36.7-103.7), while median cumulative BED 3 was 172Gy (127-203.7). 23 (43%) patients received concurrent TMZ, while 32 (60%) patients received post RT maintenance / salvage chemotherapy. With mean follow up of 13 months , overall median survival was 14.3 months (95% CI – 9.3 -19) for the whole patient cohort. The median survival for Combs prognostic groups were 14.3 months (Group a) , 13 months (Group b) , 3.5 months (Group c) and 3 months (Group d). Univariate analysis, statistically significant higher overall survival was noted in patients with KPS score >80 [48.6 vs 8.3 mths, p < 0.001] and those receiving salvage chemotherapy [29.7 vs 15.1 mths, p = 0.02]. A trend towards improved survival was noted for those who received ReRT BED 3 > 75Gy [41.4 vs 12.1 mths, p= 0.08] and time gap of >18 months between initial RT and ReRT [23.8 vs 12.8 mths, p = 0.2]. No statistically significant differences were noted based on fractionation schedule. 7 patients had symptomatic radiation necrosis. Conclusion ReRT is an important salvage option in recurrent gliomas with acceptable toxicities especially for patients with good KPS , reasonably good time gap for ReRT and higher ReRT BED > 75 Gy. The Modified Combs prognostic factors appears to be accurately predicting the overall survival and may be applicable in Indian patients in selecting appropriate patients who would benefit from ReRT. PO-1054 Skull base meningiomas trated with Radiosurgery/Fractionated Stereotactic Radiotherapy M. Rodriguez 1 , M. Rico 2 , A. Barco 1 , L. Rosas 3 , E. Burillo 3 , E. Martinez 3 1 Complejo Hospitalario de Navarra, Radiation Oncology , Pamplona, Spain; 2 Complejo Hospitalario de Navarra , Radiation Oncology , Pamplona, Spain; 3 Complejo Hospitalario de Navarra, Radiation Oncology, Pamplona, Spain Purpose or Objective In cases of meningioma associated with increased surgical risk, as those located in the base of skull, stereotactic radiosurgery(SRS) and fractionated stereotactic radiotherapy(FSRT) can be regarded as an effective alternative with 5-years local control greater than 90%. Therefore, our objective is to review the outcome of patients with skull base meningiomas treated with SRS or FSRT at our center in the last 10 years and compare them with current literature. Materials and Methods We retrospectively reviewed skull base meningiomas treated with SRS and SRS from 2010 to 2020. Between 2010 and 2018 patients were treated in a Varian linear accelerator Trilogy with an optically-guided bite-block frameless system (Zmed). From 2019 onwards, patients were treated in a Varian Truebeam linear accelerator with the ExacTrac intracranial frameless system form Brainlab based on X-ray image guidance. We used Kaplan-Meier and Log-rank test to analyse local control (LC) and overall survival (OS) and a multivariate analysis to find association between possible risk factors (Linear accelerator, age, tumor volume, dose fractionation, grade, intention of treatment) and LC. Results 40 patients underwent SRS/FSRT, 36 FSRT and 4 SRS. 29 (72.5%) were female and 11 (27.5%) males, with a mean age of 60 years. 38(95%) were WHO Grade I or assumed as Grade I. 33(82.5%) underwent exclusive RT and 7(17.5%) adjuvant RT. Mean dose in SRS was 14Gy (12-15) and for FSRT was 54Gy (25-59.4). Mean tumor volume was 12,48cc3. Mean dose to chiasm and optic nerves was 41.43Gy. There were 4(10%) progressions, 4(10%) partial responses and 32(80%) stabilizations. According to subjective clinical status, 23 (57.5%) remained stable, 13(32.5%) improved and 4(10%) got worse. No patient presented radiologically diagnosed radionecrosis. With a median follow up of 57.4 months, the 5 and 8-years OS were 83.9%. The median OS was not reached. 5 and 8-years LC were 90.2%. We found significant statistical association between LC and intention of treatment being favorable for patients undergoing exclusive SRS/FSRT (Log-rank test: p=0,011). We also found significant statistical association, between LC and tumor volume (Log-rank test: p=0,00). In the multivariate analysis, we found no significant statistical association, between possible risk factors and LC.