ESTRO 36 Abstract Book

S605 ESTRO 36 _______________________________________________________________________________________________

tumor, received SRS/SRT. The prescribed total dose and fractionation, based on BMs size and proximity to organs at risk, ranged from 15Gy in 1 fraction to 30Gy in 5 fractions. A FFF-Volumetric Modulated Arc Therapy (VMAT) plan was generated with one or two coplanar partial arcs. Toxicity was assessed according to CTCAE v4.0. Results From April 2014 to February 2016, 45 patients (89 BMs) were treated with SRS/SFRT linac-based FFF-delivery. The mean beam-on-time was 140 seconds for each lesion (range 90-290 seconds) and the average brain Dmean was 1Gy (range 0.1 - 4.8 Gy). With a median follow-up time of 12 months (range 1-27 months), the median overall survival was 14 months and the 6-month overall survival was 77% and. At the time of analysis local control was reported in 83 BMs (93.2%) and 6-month actuarial rates was estimated in 76.4%. Finally, the median intracranial disease control was 11 months. Acute and late toxicities were acceptable without severe events (no adverse events ≥ G2 were recorded). Conclusion These preliminary results confirmed the feasibility and safety of linac-based SRS/SFRT with FFF delivery for BMs patients. A longer follow-up is necessary to assess the definitive efficacy and tolerability of SRS/SFRT with FFF in BM patients. EP-1105 Treatment Outcomes and Prognostic Factors of Atypical Meningioma: A Single-Institution Experience H.J. Kang 1 , B.O. Choi 1 1 The Catholic University of Korea- Seoul St.Mary's Hospital, Radiation onconlogy, SEOUL, Korea Republic of Purpose or Objective We aimed to evaluate the treatment outcomes and prognostic factors in patients with atypical meningioma. Material and Methods From 2001 to 2016, 131 patients were retrospectively reviewed in this study. All patients were treated with surgical resection and histologically confirmed as atypical meningioma. The histology grading was defined by the 2000/2007 WHO classification. Ninety-five patients (75.5%) underwent gross-total resection (GTR) and 36 patients (27.5%) underwent subtotal resection (STR). Of the 36 patients treated with STR, 20 (15.7%) received adjuvant radiation therapy (ART). Results The median follow-up time was 36 months (range, 6-152 months). The 3- and 5-year progression-free survival (PFS) rates were 81.8% and 74.6%, respectively, and the 3- and 5-year overall survival rates were 93% and 86.5%, respectively. Only the surgical resection status was significantly associated with disease progression ( p= 0.002). In the STR subgroup, ART was also significantly associated with progression ( p= 0.003). When stratified into 3 groups according to the surgical resection status and ART, the patients treated with STR alone showed significantly lower PFS, while those treated with GTR and STR plus ART did not (3-year PFS, 30.8% vs 91% vs 83.6%; p =0.013). Conclusion Although the most important prognostic factor related to progression was the surgical resection status, ART in patients with STR improved PFS, which is similar to those with GTR. Routine use of ART after STR is recommended. EP-1106 Local control and overall survival after frameless radiosurgery A. Bilger 1 , F. Frenzel 1 , O. Oehlke 1 , R. Wiehle 1 , D. Milanovic 1 , V. Prokic 2 , C. Nieder 3 , A.L. Grosu 1 1 University Medical Center Freiburg, Department of

Purpose or Objective Hippocampal-dependent functions, including learning, memory and spatial informations processing, could be affected by brain radiotherapy. Aim of the present study is to evaluate the dose to omolateral and contralateral hippocampus (O-H, C-H, respectively) during Stereotactic Radiotherapy (SRT) or Radiosurgery (SRS) for brain metastases (BM). Material and Methods Patients eligible for SRS/SRT treatment had a number of BM <5, with a size ≤30mm, Karnosky Performance Status (KPS) ≥ 80 and a life expectancy over 3 months. Gross Tumour Volume (GTV) was delineated by the fusion between Magnetic Resonance Imaging and Computed Tomography. A Planning Target Volume (PTV) was obtained from GTV by adding a 2mm isotropic margin. The total dose ranged between 18-27 Gy in 1-3 fractions. For each BM, a Volumetric modulated arc therapy plan was generated with one or two arcs and hippocampus sparing was not considered during optimizations phase. For the dosimetric evaluation of O-H and C-H, the D median , D mean , D 0.1cc and the V 1Gy , V 2Gy , V 5Gy and V 10Gy were analyzed. Results From April 2014 to December 2015, 81 BM in 41 patients were treated with SRS/SRT and selected for the present analysis. The average value of PTV dimension and hippocampus volumes were (5.8 + 9.5) cc and (1.1 + 0.3) cc, respectively. For the O-H, the average values of D median , D mean and D 0.1cc were (1.5 + 3.65) Gy, (1.54 + 3.6) Gy, (2.2 + 4.7) Gy, respectively, while the V 1Gy , V 2Gy , V 5Gy and V 10Gy values were (25 + 40) %, (18.9 + 35) %, (8.9 + 25.3) % and (2.1 + 11.8) %, respectively. For the C-H, the average D median , D mean and D 0.1cc were (0.7 + 1.5) Gy, (0.7 + 1.4) Gy, (0.9 + 1.8) Gy, respectively, while the average values of V 1Gy , V 2Gy , V 5Gy and V 10Gy were (18 + 35) %, (10.2 + 27.7) %, (2.8 + 15.4) % and (1.4 + 11.6) %, respectively. The differences between O-H and C-H, in terms of received dose, was statistically significant (p=0.03). Moreover, the PTV dimension (>5cc or >6cc) did not influenced the dose of hippocampus (p= 0.06; 0.2, respectively). Conclusion During SRT/SRS treatments for BM, hippocampus received a very low dose and its clinical significance seems to be negligible, even if it is still under investigation. However, considering the increasing use of SRS/SRT for multiple BM, including also patients with up to 10 BM, the dose to hippocampus need to be seriously evaluated in the treatment planning. EP-1104 SABR for brain metastases with VMAT and FFF: feasibility and early clinical results N. Giaj Levra 1 , A. Fiorentino 1 , G. Sicignano 1 , U. Tebano 1 , S. Fersino 1 , R. Mazzola 1 , F. Ricchetti 1 , D. Aiello 1 , S. Naccarato 1 , R. Ruggieri 1 , F. Alongi 1 1 Sacro Cuore Don Calabria Cancer Care Center Hospital, Radiation Oncology, Negrar-Verona, Italy Purpose or Objective For selected patients with brain metastases (BMs), the role of stereotactic radiosurgery (SRS) or stereotactic fractionated radiotherapy (SFRT) is well recognized. The recent introduction of Flattening-Filter-Free (FFF) delivery during linac-based SRS or SFRT allows shorter beam-on-time, improving patients’ comfort and facility workflow. Aim of the present study was to analyze SRS/SFRT linac-based FFF-delivery for BMs in terms of dosimetric and early clinical results. Material and Methods Patients with life expectancy > 3 months, number of BMs < 5, diameter < 3cm and controlled or synchronous primary neurocognitive