Abstract Book

S1055

ESTRO 37

Conclusion The plan quality was slightly better in combination of 6MV&10MV-FFF as compared to 6MV-FFF and 10MV-FFF. But no significant difference was observed use of different flattening filter free (FFF) photon energy for VMAT prostate cancer. EP-1943 Is dose escalation in intracranial pediatric ependymoma feasible with advanced radiation techniques? F. Tensaouti 1 , A. Ducassou 2 , L. Chaltiel 3 , S. Bolle 4 , J.L. Habrand 5 , C. Alapetite 6 , B. Coche-Dequeant 7 , V. Bernier 8 , L. Claude 9 , C. Carrie 9 , X. Muracciole 10 , S. Supiot 11 , A. Huchet 12 , J. Leseur 13 , C. Kerr 14 , G. Hangard 2 , A. Lisbona 11 , F. Goudjil 6 , R. Ferrand 2 , A. Laprie 15 1 ToNIC- Toulouse NeuroImaging Center- Université de Toulouse- Inserm- UPS-, ToNIC- Toulouse NeuroImaging Center- Université de Toulouse- Inserm- UPS-, Toulouse, France 2 Institut Universitaire du Cancer de Toulouse Oncopole, Department of Radiation Oncology, Toulouse, France 3 Institut Universitaire du Cancer de Toulouse Oncopole, Department of biostatistics, Toulouse, France 4 Institut Gustave Roussy, Department of Radiation Oncology, Paris, France 5 Centre Francois Baclesse, Department of Radiation Oncology, Caen, France 6 Institut Curie, Department of Radiation Oncology, Paris, France 7 Centre Oscar Lambret, Department of Radiation Oncology, Lille, France 8 Centre Alexis Vautrin- Vandoeuvre, Department of Radiation Oncology, Nancy, France 9 Centre Leon Berard, Department of Radiation Oncology, Lyon, France 10 CHU La Timone, Department of Radiation Oncology, Marseille, France 11 Institut de cancerologie de l'ouest, Department of Radiation Oncology, Nantes, France 12 CHU Bordeaux, Department of Radiation Oncology, Bordeaux, France 13 Centre Eugene Marquis, Department of Radiation Oncology, Rennes, France 14 Institut regional du Cancer Montpellier- Val d'Aurelle, Department of Radiation Oncology, Montpellier, France 15 Institut Universitaire du Cancer de Toulouse Oncopole, Department of Radiation Oncology-, Toulouse, France Purpose or Objective For pediatric ependymoma, previous publications described a dose effect on survival [1] and a majority of relapses within the high dose regions [2]. A survival benefit was described with SBRT on residue [3]. MacDonald et al [4] found that proton beams and IMRT have similar target coverage, but normal tissue sparing was better in proton. This prompted us to perform a dose escalation approach with an in-silico dosimetric comparison between Volumetric Modulated Arc Therapy (VMAT) photon therapy and Intensity Modulated Proton Therapy (IMPT). Material and Methods The cohort included 101 patients (60.4 % with posterior fossa), from the national multicentric PEPPI database [2].The dose to PTV59.4 was 59.4/1.8 Gy and the dose to simultaneous integrated boost volume, PTV67.6 was 67.6/2.05 Gy (this dose being chosen as an equivalent to sequential SBRT boost in the European trial NCT02265770). The Gross Total tumor (GTV) was defined as the tumor bed plus residual tumor, CTV59.4 was GTV+5 mm, PTV59.4 = CTV59.4 +3 mm. PTV67.6 was GTV+ 3 mm. Ballistic choices were made regarding the risk on brainstem, incorporating the possibility of a higher RBE at the end of the range of the spread out Bragg peak. All treatment plans were optimized with the physical dose-volume objectives/constraints (for targets as well as

relevant.

EP-1942 Impact of different FFF photon beam energy on VMAT prostate cancers treatment C. Saravanan 1 , P. Mohandass 1 , N.K. Bhalla 1 , A. Puri 1 1 FORTIS HOSPITAL, Radiation Oncology, Mohali - Punjab, India Purpose or Objective To evaluate impact of different flattening filter free (FFF) photon beam energy on volumetric arc therapy (VMAT) for prostate cancer. Material and Methods For this study, three prostate patients with no nodal involvement treated with 79.20Gy/44fractions were chosen from clinical data base. All the plans were generated using VMAT technique in Monaco™ V5.1 treatment planning system(TPS) for Elekta Versa HD™ linear accelerator with 0.5cm leaf width at isocenter. The VMAT plan was generated using 6MV-FFF photon along with partial and full arc. By keeping all other planning parameter constant, only by varying energy, plans were re-planned for 10MV-FFF and 6MV&10MV-FFF photon energy. For plan comparison, Conformity (CI), Homogeneity index (HI), dose coverage to planning target volume (PTV), Mean dose, max dose and dose volume received by organ at risk (OAR) for bladder, rectum, left femur, right femur and small bowel were analyzed. In addition, integral dose to normal tissue (liter-Gray), total monitor unit (MU) and delivery time (mins) were analyzed. Results The CI for PTV was 1.0876±0.0399, 1.0776±0.0530 and 1.1315±0.0081 for 6MV-FFF, 10MV-FFF and 6MV&10MV- FFF respectively. Similarly, HI was 0.0989±0.0270, 0.1015±0.0281 and 0.0944±0.0231. The mean dose and dose received by 95% volume to PTV was slightly increased for 6MV&10MV-FFF as compared to 6MV-FFF and 10MV-FFF. In addition, mean dose and dose volume received by bladder, rectum, left femur, and right femur showed lesser dose in 6MV&10MV-FFF as compared to 6MV-FFF and 10MV-FFF. Similarly, max dose to small bowel was less for 6MV&10MV-FFF as compared to 6MV- FFF and 10MV-FFF. However, no significant difference was observed in integral dose, MU and treatment delivery time.