ESTRO 36 Abstract Book

S610 ESTRO 36 _______________________________________________________________________________________________

2 Fondazione Policlinico A. Gemelli, UOC Fisica Sanitaria - Gemelli ART - Radiation Oncology, Rome, Italy 3 Fondazione Policlinico A. Gemelli, Rome, Italy 4 Fondazione Policlinico A. Gemelli, TSRM - Gemelli ART - Radiation Oncology, Rome, Italy 5 Fondazione Policlinico A. Gemelli, KBO Labs - Gemelli ART - Radiation Oncology, Rome, Italy 6 Università Cattolica del Sacro Cuore, Gemelli ART - Radiation Oncology, Rome, Italy 7 Università Cattolica del Sacro Cuore, Rome, Italy Purpose or Objective To evaluate the feasibility of planning hypofractionated intensity-modulated radiotherapy (IMRT) for brain metastases (BM) with a tri-cobalt-60 (tri-60Co) system equipped with real-time magnetic resonance imaging (MRI) guidance, as compared to linear accelerator (LINAC) based IMRT and Volumetric Modulated Arc Therapy (VMAT). Material and Methods Patients treated with LINAC-based IMRT and VMAT were replanned using a tri-60Co system. Radiotherapy plans were structured with a mono-isocentric IMRT technique using 21 beams. Dose prescription followed ICRU 83 indications; 25.5 Gy in 3 fractions. Both LINAC and ViewRay plans were considered acceptable when median absorbed dose of Planning Target Volume (PTV), D50%, was equal to prescription dose, D98% was ≥ 95%, and D2% to optic chiasm and optic nerves, brainstem and normal brain were <19,5Gy, <23Gy and <21Gy, respectively. D50% of normal brain and to hippocampus were setted as low as possible. The plans were evaluated for target volume (TV) coverage, Paddick dose conformity (CI), homogeneity (HI), dose to organ at risk (OAR) and to normal brain. Plan comparisons was performed. Results In all, 16 brain metastases were evaluated. The median PTV was 4,0 cc (range 1.7-13.6cc). Slightly higher median value of HI and lower median value of PCI were observed when tri-60Co was compared to LINAC plans (0.07 vs 0.03; p= 0.59 and 0,50 vs 0,54; p=0.73). For the OAR, no statistically significative differences were registered in D2% of brainstem, optic chiasm, optic nerves, hippocampus and normal brain even if higher doses were noted in tri-60Co vs LINAC plans (1.04 Gy vs 0.26 Gy, p=0.6; 0.58 Gy vs 0.18 Gy, p=0.58; 0.54 Gy vs 0.12 Gy, p= 0.56; 1.66 Gy vs 0.41 Gy , p=0.64; 17.37 Gy vs 11,73 Gy, p= 0.61; respectively). Similarly, D50% and V21Gy of normal brain were higher in tri-60Co plans (3.17 Gy vs 0.18 Gy, p=0.62 and 14.20cc vs 6.15cc, p= 0.57). There were statistically significant differences in V100% between tri-60Co and VMAT plans (2.01cc vs 1.67cc, p=0.005) whilst non statistical significative difference was observed between tri-60Co and LINAC-based IMRT plans (2.01 cc vs 1.72 cc, p= 0.56). V50% was marginally statistically lower in LINAC than in tri-60Co plans (30.79 cc vs 90.05 cc, p= 0.49). Conclusion All ViewRay plans were deemed acceptable for clinical delivery. It should be noted that every dose-volume criteria studied in this article was lower in the LINAC plans than in the tri-60Co SBRT plans, with statistical significance noted only for the 100%- and 50%-isodose volume without a statistically significative impact on OAR or TV coverage. The MRI may afford the opportunity to both reduce PTV margins and improve critical organ sparing, so a new study about LINAC and tri-60Co with reduced PTV margins is ongoing.

EP-1116 Reirradiation and concurrent bevacizumab high-grade recurrent gliomas: experience and perspectives. A. Schernberg 1 , F. Dhermain 1 , S. Dumont 2 , A. Patrikidou 2 , J. Domont 2 , J. Pallud 3 , E. Deutsch 1 , G. Louvel 1 1 Gustave Roussy, Radiotherapy, Villejuif, France 2 Gustave Roussy, Oncology, Villejuif, France 3 Saint Anne, Neurosurgery, Paris, France Purpose or Objective Analyze feasibility and prognostic factors of concurrent re- irradiation and bevacizumab (BVZ) forrecurrent high- grade gliomas. Material and Methods Between 2009 and 2015, 35 patients (median age 57 years, 21 men and 14 women) with WHO grade-3 (n=11) or grade- 4 gliomas (n=24) were included in this retrospective single-center study. All patientsreceived BVZ (median number of treatments = 12) concomitant with re- irradiation (median dose =45Gy, median number of fractions = 18) experiencing recurrence after a first irradiation (median = 22months, median dose = 60Gy). Results Median follow-up was 9.2 months. Median overall survival (OS) was 10.5 months (95%CI: 4.9 - 16.1)and progression- free survival 6.7 months (95%CI: 2.9 - 10.5) from re- irradiation. Median OS frominitial diagnosis was 44.6 months (95% CI 32 to 57.1). No grade ≥ 3 toxicities were reported.Prognostic factors in univariate analysis significantly correlated with better OS were: age ≤ 55(p=0.024), initial surgery (p=0.003), and equivalent 2Gy dose (EQD2) ≥ 50 Gy at reirradiation(p=0.046). Naïve BVZ patients at time of re-irradiation had significantly increased OS from reirradiationcompared to patients treated with re-irradiation after BVZ failure (15.1 vs. 5.4 months, p<0.001) aswell as OS from initial diagnosis (58.9 vs. 33.5 months, p=0.006). This outcome was similar in patientswith initial glioblastomas (p=0.018) or anaplastic gliomas (p=0.021). There was no correlation betweenOS and GTV or PTV volume, frontal localization, or number of salvage therapies before reirradiation(p > 0.05). Conclusion Concomitant re-irradiation with BVZ in high grade recurrent gliomas shows encouraging results interms of survival and toxicities. Our datas suggests that re- irradiation should be favored at initiation ofBVZ, with ≥ 50Gy EQD2. EP-1117 Sequential Proton Boost after Standard Chemoradiation for High-Grade Glioma S. Adeberg 1 , D. Bernhardt 1 , S. Harrabi 1 , M. Uhl 1 , A. Paul 1 , N. Bougatf 1 , V. Verma 2 , T. Haberer 3 , S. Combs 4 , K. Herfarth 1 , J. Debus 1 , S. Rieken 1 1 University Hospital Heidelberg, Department of Radiation Oncology, Heidelberg, Germany 2 University of Nebraska Medical Center, Department of Radiation Oncology, Omaha, USA 3 Heidelberg Ion-Beam Therapy Center HIT, Heidelberg Ion-Beam Therapy Center HIT, Heidelberg, Germany 4 Technische Universität München, Department of Radiation Oncology, Munich, Germany Purpose or Objective To retrospectively assess the feasibility and safety of a sequential proton boost following conventional chemoradiation in high-grade glioma (HGG). Material and Methods Sixty-six consecutive patients with HGG were treated at the Department of Radiation Oncology, University Hospital Heidelberg, Germany with 50.0 Gy photons (range: 50.0 – 50.4 Gy) in 2.0 Gy (range: 1.8 – 2.0 Gy) fractions (median