ESTRO 2020 Abstract book

S241 ESTRO 2020

PH-0412 MRI-only in prostate radiotherapy planning using multiple individual atlases: a preliminary study S. Nici 1 , A.F. Monti 1 , D. Lizio 1 , R. Pellegrini 2 , M.G. Brambilla 1 , C. Carbonini 1 , M.J. Arias Garces 1 , M.M.J. Felisi 1 , B. Bortolato 3 , C. Frassica 4 , C. Coletti 3 , A. Vanzulli 4 , A. Torresin 1 1 ASST Grande Ospedale Metropolitano Niguarda, Medical Physics, Milan, Italy ; 2 Elekta, Clinical Science, Milan, Italy ; 3 ASST Grande Ospedale Metropolitano Niguarda, Radiotherapy, Milan, Italy ; 4 ASST Grande Ospedale Metropolitano Niguarda, Radiology, Milan, Italy Purpose or Objective In this work, we aim to implement a magnetic resonance imaging (MRI)-based workflow in prostate cancer radiation therapy for planning purposes by using a hybrid technology. In computed tomography (CT) the voxel value is related to the tissue electron density; on the other hands MRI voxel is related to tissue proton density, and not useful for dose calculation. Therefore, it is necessary to convert MRI into electron density or HU by creating a surrogate of CT, a synthetic CT (sCT), to allow the treatment planning system (TPS) to calculate the dose distribution. Material and Methods To create sCTs from MRI, we propose a hybrid method that is a combination of bulk and multi-atlas-based approach. MR images from 10 volunteers were acquired by using an optimized 3D T1 VIBE-Dixon sequence with a 1.5T Siemens Aera MRI scanner with a FOV enclosing the whole body contour, flat table couch and fixation devices for feet and knees. Contours of these volunteers were delineated by identifying bone structures and main organs-at-risk (OARs), such as bladder, femoral heads, femurs, pelvic bones, rectum and sacrum, to create atlases as reference database for an auto segmentation software (ADMIRE, Elekta). This software approximates the anatomy contours by comparing several individual atlases, applying elements of maximum likelihood forms to a new patient image-set, and creates a structure set to fit the actual patient’s anatomy. Finally, sCTs were generated starting from the auto- segmented bones and OARs in the treatment planning system (Monaco, Elekta). A bulk electron density was assigned to each volume. Electron densities were averaged over 19 patients CTs who underwent to prostate radiotherapy (Fig.1). Three 10MV photon VMAT prostate plans were optimized for three patients on planning CT and recalculated on the corresponding sCT. Dosimetric differences to planning CT were evaluated by using quantitative methods such as dose-volume histogram (DVH) and 2D local gamma analysis.

Conclusion This study demonstrates that MRI-only planning for prostate patients is feasible using our proposed MRI optimized sequence and hybrid bulk - multi-atlas method. In particular sCT-based treatment plans provide dosimetric and gamma analysis values in close agreement to original CT-based. This method provides also quite nice contours with few corrections before planning: quantitative analysis will be finalized with an expanded cohort of patients to increase the efficiency of the atlas. PD-0413 The role of different chemotherapy protocols for concurrent CRT in locally advanced NSCLC E. Gkika 1 , S. Tanja 1 , K. Stephanie 2 , A. Schaefer-Schuler 3 , M. Mix 4 , A. Küsters 5 , M. Tosch 6 , S.M. Eschmann 7 , Y. Bultel 8 , P. Hass 9 , J. Fleckenstein 2 , A. Thieme 10 , M. Stockinger 11 , K. Dieckmann 12 , M. Miederer 13 , G. Holl 14 , C. Rischke 1 , S. Adebahr 1 , S. Lenz 15 , C. Broichhagen 15 , H. Binder 15 , J. König 16 , A. Grosu 1 , U. Nestle 1,5 1 Uniklinik Freiburg, Radiation Oncology, Freiburg, Germany ; 2 Saarland University Hospital, Department of Radiation Oncology, Homburg/Saar, Germany ; 3 Saarland University Hospital, Department of Nuclear Medicine, Homburg/Saar, Germany ; 4 Uniklinik Freiburg, Department of Nuclear Medicine, Freiburg, Germany ; 5 Kliniken Maria Hilf, Department of Radiation Oncology, Mönchengladbach, Germany ; 6 Helios University Hospital Wuppertal, Department of Nuclear Medicine, Wuppertal- , Germany ; 7 Marienhospital Stuttgart, Department of Nuclear Medicine, Stuttgart, Germany ; 8 Klinikum Mutterhaus der Boromäerinnen, Department of Radiation Magdeburg, Germany ; 10 Charité University Hospital-, Department of Radiation Oncology, Berlin, Germany ; 11 University Hospital Mainz-, Department of Radiation Oncology, Mainz, Germany ; 12 Medical University of Vienna, Department of Radiotherapy, Vienna, Germany ; 13 University Hospital Mainz, Department of Nuclear Medicine, Mainz, Germany ; 14 Helios Kliniken Schwerin, Department of Nuclear Medicine, Schwerin, Germany ; 15 University of Freiburg, Institute of Medical Biometry and Statistics IMBI, Freiburg, Germany ; 16 University of Mainz, Institute of Medical Biostatistics- Epidemiology and Informatics IMBEI-, Mainz, Germany Purpose or Objective Concurrent chemotherapy is the standard of care for locally advanced non-small cell lung cancer (NSCLC) treated with definitive radiotherapy. The optimal chemotherapy protocol for use with concurrent therapy is not known. In this analysis we evaluated the role of Oncology, Trier, Germany ; 9 University Hospital Magdeburg, Department of Radiation Oncology, Poster discussion: CL: Lung

Results The mean deviation of DVH-parameters for PTV and OARs for the three patients were less than 1.5%. 2D local gamma analysis, using an acceptance criterion of 2% and 2mm, provided average pass rates of 99.9% for the axial and coronal planes and 100% in the sagittal plane. Under the strict passing criteria of 1% and 1 mm, the average pass rate was 98.6%, 96.7% and 95.9% for the axial, coronal and sagittal planes, respectively.