Abstract Book

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treating bilateral schwannomas simultaneously by cyberknife. Material and Methods 5 Patients (4 Female,1 Male) diagnosed with bilateral acoustic schwannomas were planned and treated with DOTA PET and MRI based Cyberknife to B/L Schwannomas simultaneously from 2010 to 2015.2 were part of NF–2.4 patients were post decompression. Constraints were prescribed to normal structures like brainstem and cochlea. All patients were followed up every 3 months with 6 monthly MRI Scans. They were also assessed for toxicity.2 patients are on follow up for 5.5years,1 patient 4 years,1 patient 2 years, others since 1.5 years. Results 5 Patients with 9 lesions were treated by Cyber knife guided with 25Gy/5 frs ,prescription isodose ranges from 75-88%. Size of the lesions ranged from 1.5 to 3.2 cms. Mean volume of the GTV was 15.4cc. Max Brain stem dose in 5 patients was 24.8, 27.5, 11.8, 19.05, 12 Gy respectively. Mean doses to brainstem was 11.9, 10.4, 8.0, 8.71, 4.8 Gy respectively. Cochlear doses were maintained within normal limits. All patients had complete symptomatic response and partial radiological response. None of the patients had brain stem changes or any other toxicity.All patients maintained good quality of life. Conclusion Bilateral vestibular schwannomas can be treated simulta- neously with cyberknife 25Gy/5 fractions with normal brain stem doses and similar toxicity and response profiles. However large number of cases with long follow up is required. EP-1232 Fractionated Stereotactic Radiotherapy for Vestibular Schwannoma. Toxicity and Complications. H. Pérez Montero 1 , N. Gascón 2 , S. Guardado 2 , A. Cabezas 2 , R. D'Ambrosi 2 , V. Rodríguez 2 , J. Pérez- Regadera 2 1 Institut Català d´Oncologia, Radiation Oncology, Barcelona, Spain 2 Hospital Universitario 12 de Octubre, Radiation Oncology, Madrid, Spain Purpose or Objective Vestibular Schwannomas (VS) are benign neoplasm originated in nerve sheath, whose incidence has increased since MRI generalization. Patient with VS suffer from auditory and neurological alterations derived from the tumor itself and its treatments (Surgery and/or Radiotherapy techniques). Objective: Descriptive analysis of auditory toxicity and complications of Fractionated Stereotactic Radiotherapy (FSRT) for VS in our centre. Material and Methods Between 2004 and 2015, we evaluated 137 consecutive patients affected with VS for treatment by FSRT. Finally, 114 of them (M/F 56/58; median age 56 years) were treated by this technique. 1 patient (0.8%) was also diagnosed with Neurofibro- matosis (NF) type I, 3 patients (2.6%) with NF type II and 3 (2.6%) with Meningioma. Baseline hearing was normal in 12 patients (10.5%), 49 (42.9%) had a loss of less than 30 dB, a loss greater than 30 dB was observed in 30 (26.3%), and complete deafness in 23 (20.2%). 53 (46.5%) suffered tinnitus prior to treatment. 36 (31.6%) patients presented mild balance alteration in and 8 (70.2%) presented severe balance alteration. 23 (20.2%) had incomplete facial paralysis and 8 (7%) complete facial paralysis. Tumor size was less than 1 cm in 16 cases (14%), between 1-1.99 cm in 50 (43.9%), between 2-2.99 cm in 34 (29.8%), between 3-3.99 in 9 (7.9%) and greater than 4 cm in 5 (4.4%).

According to Mathies classification patients were distributed: T1; 21 (18.4%) T2; 25 (21.9%), T3; 46 (40.4%), T4; 15 (13.2%). 19 (16.7%) of these patients had received surgery for VS once and 5 (4.4%) twice. 16 (14%) patients had also affection of V cranial nerve, 1 (0.8%) had affection of IX cranial nerve, 1 (0.8%) had affection of XII cranial nerve, and affection of several cranial nerves was observed in 1 (0.8%) patient. For Radiotherapy administration, patients were immo- bilized by Gill-Thomas-Cosman frame. Daily fractions of 2 Gy were delivered in all cases. Average total dose was 53.5 Gy (R 50-66). After treatment, patients were followed at regular intervals. Median follow-up at the time of analysis was 6.4 years (R 0.4-11.6). Endpoints of the study were auditory toxicity and treatment-related complications. Results Hearing after treatment with FSRT remained unchanged in 96 (84.2%) of patients, improved in 5 (4.4%) and worsened in 13 (11.4%). 108 patients (94.7%) had no RT-related complications. 1 (0.8%) patient presented with brainstem edema and 5 cases (4.4%) of asymptomatic radiological necrosis were observed. 100% of these complications occurred in patients who had undergone at least one surgical procedure for VS previously (p=0.041). No other factor associated with complications or hearing function alteration was observed in subgroup analysis. Conclusion According to our data, FSRT, as treatment for VS, presents high preservation of hearing with low rate of complications. Previous surgical procedure was associated with RT-related complications. EP-1233 DKI in GBM patients: Could it be a new biomarker for radiobiology response after irradiation? I. Djan 1 , M. Bjelan 2 , S. Lucic 2 , O. Sveljo 2 , K. Koprivsek 2 , N. Vuckovic 3 , M.A. Lucic 2 1 Institute of Oncology Vojvodina, Radiotherapy Department, Sremska Kamenica, Serbia 2 Institute of Oncology Vojvodina, Center for Imaging and Diagnostics, Sremska Kamenica, Serbia 3 University of Novi Sad, Faculty of Medicine, Novi Sad, Serbia Purpose or Objective The aim of this study was to detect early microstructure changes in white matter using diffusion kurtosis imaging (DKI), which occur as radiobiological response within the areas with differently delivered irradiation doses, during and after chemoirradiation treatment of glioblastoma multiforme (GBM) patients. Exact mechanisms that lead to post-irradiation changes in white matter are not well known. Also, it is not known which radiotherapy doses and which dose of daily fractions induce changes that can be detected by DKI. Material and Methods Fifteen GBM patients underwent DKI examination on 3T MRI unit before the chemoradiotherapy treatment, after 16 delivered fractions, and immediately after 33 delivered fractions. Radiotherapy contained fractional focal irradiation for a total dose of 60Gy. Delineation was performed regarding RTOG and EORTC recommendations. Concomitant temozolomide was applied in 75mg/m 2 in 42 consecutive days. Regions of interest (ROI) within overall irradiation doses of 20Gy/40Gy/60Gy were determined using fused dose-volume histograms/FLAIR images, and DKI parameters-radial kurtosis (K rad ), axial kurtosis (K ax ), and mean kurtosis (MK) were measured. It was calculated that daily dose for white matter for total dose of 20Gy was approximately 0.6Gy, for total dose of 40Gy daily dose was 1.2Gy, and for total dose of 60Gy daily dose was approximately 1.8Gy.