ESTRO 2020 Abstract book

S521 ESTRO 2020

similarly in both groups (53% vs 59%, p = 0.55, and 19% vs 16%, p = 0.79, respecively). One-year local control rate and dissemination recurrence free rate were significantly lower in GTR than in non-GTR (59% vs 33%, p = 0.042, and 98% vs 80%, p = 0.010, respectively). There was no significant difference for one-year distant recurrence free rate between two groups (87% vs 85%, p = 0.99). Conclusion The patients with GTR have improved local control and survival time. In patients treated without GTR, recurrence of meningeal dissemination seemed to be increasing. PO-0888 Protontherapy in Vestibular Schwannoma: volume changes, control rate, toxicity, hearing preservation D. Scartoni 1 , D. Amelio 1 , A. Turkaj 1 , I. Giacomelli 1 , M. Amichetti 1 1 Centro di Protonterapia, Protontherapy, Trento, Italy Purpose or Objective The purpose of this study was to evaluate the control rate of vestibular schwannomas (VS) after treatment with protontherapy radiosurgery (SRS) or conventional protontherapy (SRT) by using a validated volumetric measuring tool, toxicity and hearing preservation. Material and Methods Retrospectively, 16 VS patients treated with active beam protontherapy based SRS or SRT were analyzed. Baseline and follow-up magnetic resonance imaging scans were analyzed with volume measurements on contrast enhanced T1-weighted (1 mm thickness) and three-dimensional constructive interference in steady-state (3D-CISS) magnetic resonance imaging. The volume measurements were performed on axial coupes, using a computer system fitted with specialized software: Raystation TPS v7.0; volumetric VS analysis was performed in cubic centimeter. Significant growth was defined as a volume change of 19.7% or more. Toxicity was assessed according to CTCAE version 4.03; hearing preservation rates was evaluated using the Gardner-Robertson grading system as determined by audiogram results. Twelve patients (75%) received 50.4 GyRBE in 28 fractions, 4 patients (25%) performed protontherapy SRS (12 GyRBE in single fraction). Results At the median follow-up of 24 months (range 9-53), significant shrinkage was seen in 20%, stable VS in 53%, and significant growth in 27% of the patients. In 46% of all patients, transient swelling was observed. However, in the significant growth group no additional treatment was required. No significant shrinkage was observed in protontherapy SRS group. Registered acute side effects include G1 (10%) fatigue, G1 (14%) muffled, G2 (14%) headache, G2 (7%) nausea. There were no G 3 or higher acute toxicities. Registered late side effects include G 1 (7%) and G2 (14%) dizziness, G2 (7%) vertigo, G2 (7%) nausea, facial nerve deficit (House Brackmann scale G2) (7%). Absolute hearing, normal facial and trigeminal preservation rates were 67%, 86% and 93% respectively. Conclusion Active beam protontherapy is feasible and safe treatment for patients with untreated VS. Good control rates are reported for protontherapy based SRS or SRT in VS, in which the lower rate of radiological growth control is attributed to the use of the more sensitive volume measurements. Transient swelling is a common phenomenon and should not be mistaken for treatment failure. Longer FU is necessary to assess definitive efficacy and toxicity. PO-0889 Clinical outcome of diffuse midline glioma, H3K27M-mutant treated with post-operative radiotherapy K. UtaivichakuL 1 , C. Chakkabat 1 , A. Prayongrat 1 , K. Shotelesuk 1 , C. Lertbutsayanukul 1 , D. Kannarunimit 1 , C. Nantavithya 1 , S. Kitpanit 1

1 King Chulalongkorn Memorial Hospital- Faculty of Medicine- Chulalongkorn University, Radiation Oncology, Bangkok, Thailand Purpose or Objective Diffuse midline glioma (DMG) is a newly recognized WHO grade IV primary CNS tumor by WHO 2016 classification. The characteristics of DMG include H3K27M mutation glioma, diffuse pattern and midline location. DMG is associated with poor prognosis regardless of histologic grade. Due to its central location, gross total resection is generally not possible. Post-operative treatment with radiotherapy and chemotherapy is suggested but no definite consensus of radiation dose and chemotherapy regimen are established. Nowadays, due to rarity of this disease, there is still limited clinical information and treatment outcome. This study aims to evaluate clinical outcomes and pattern of disease progression in DMG treated with post-operative radiotherapy with chemotherapy. Material and Methods Newly diagnosed DMG patients treated with post-operative radiotherapy were retrospectively reviewed. Clinical and radiological assessment was performed every 2-3 months using RANO criteria. Pattern of disease progression was classified in field, marginal and distant progression base on radiation treatment planning. Overall survival (OS) and progression free survival (PFS) was evaluated using Kaplan- Meier method. Results Between September 2016 and September 2019, 9 patients with biopsy-proven DMG with H3K27M mutation were retrospectively reviewed. DMGs were located in thalamus, pons and spinal cord, 55%, 33% and 11%, respectively. Mean age of the patient was 31 years (12-61 years). All patients had completed radiotherapy using intensity modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT) technique. The median radiation dose was 60 Gy in 30 fractions for brain lesion and 50 Gy in 25 fractions for spinal cord lesion. Fifty-five percent of the patients received chemotherapy included temozolomide and BCNU. Median follow up duration was 14.2 months (2.8-30.5 months). Median progression free survival was 21.1 months while median overall survival was not reached. 1-year and 2-year progression free survival were 87.5% and 43.8%, respectively. In-field progression of disease was detected in 2 patients (22%). No marginal and distant progression were detected. 1 of 2 of progressed patients underwent re-irradiation. Conclusion The initial clinical outcome of patients with DMG who underwent post-operative radiotherapy and chemotherapy yielded good progression free survival and overall survival compared with glioblastoma WHO grade IV in previously reported literature. The common progression pattern is in- field disease progression. PO-0890 Hypofractionated RT in elderly patients with newly diagnosed glioblastoma (GBM) with poor prognosis K. Jani 1 , R. Yadav 2 , P. Roy 3 , S. Batham 1 , M. Gandhi 1 , P. Hirpara 4 1 HCG Cancer Centre, Department of Radiation Oncology, AHMEDABAD, India ; 2 Sanjay Gandhi Post Graduate Institute of Medical Sciences, Department of Radiation Oncology, Lucknow, India ; 3 Sanjay Gandhi Post Graduate Institute of Medical Sciences, Department of Radiation Oncology, Ahmedabad, India ; 4 HCG Hospital, Department of Radiation Oncology, Bhavnagar, India Purpose or Objective Our objective was to evaluate the outcomes of hypofractionated radiation therapy (HFRT) given at therapeutic effective doses to elderly patients with newly diagnosed glioblastoma with poor prognosis. Endpoint was progression-free survival (PFS) rate.