ESTRO 2021 Abstract Book

S734

ESTRO 2021

PD-0895 Dose to heart substructures in esophageal cancer patients: Comparison between photon and protons N.S. Ubbesen 1 , M. Nordsmark 1 , M.L. Milo 1 , L. Hoffmann 2 , T.B. Nyeng 3 , D.S. Møller 4 1 Aarhus University Hospital, Department of oncology , Aarhus , Denmark; 2 Aarhus University Hospital, Department of oncology, section for medical physics , Aarhus , Denmark; 3 Aarhus University Hospital, Department of oncology, section for medical physics, Aarhus , Denmark; 4 Aarhus University Hospital, Department of oncology, section for medical physics, Aarhus, Denmark Purpose or Objective The importance of minimizing cardiac radiation exposure is increasingly acknowledged and it is widely recognized that proton therapy spares radiation dose to the whole heart. This study aims to compare the dose distribution to the whole heart with dose to 24 cardiac substructures between intensity-modulated radiotherapy (IMRT) and pencil beam scanning (PBS) proton therapy for patients with esophageal cancer. Materials and Methods Nineteen patients with newly diagnosed esophageal cancer were included in this study. All patients had chemotherapy and concomitant radiotherapy using 5-8 IMRT fields covering the planning target volume (PTV) with a homogenous dose (95-107%). For all patients, a PBS proton plan was created retrospectively. The PBS plans consisted of two posterior fields. For all patients, the IMRT and PBS plans were recalculated on all ten phases of the 4D-CT scan and the dose was accumulated to create the 4D dose. The heart and the 24 cardiac substructures were delineated in the MIM (MIM software inc., Cleveland, OH, USA) following Danish national guidelines. The 4D dose to the whole heart as well as the 24 substructures was evaluated for IMRT and PBS. Dose-volume histograms (DVH) were extracted for all plans and the mean dose and D 0.1cm3 (the highest dose delivered to the 0,1 cm 3 – near-maximum dose) were calculated for all structures. Wilcoxon signed-rank test was used to compare the mean dose and D 0.1cm3 for IMRT and PBS with P < 0,05 considered statistical significant. Results Compared with IMRT, PBS resulted in significantly lower mean radiation dose to the heart and all cardiac substructures, except for the right descending posterior branch (see fig. 1 and fig. 2 for a selection of substructures). The largest dose difference was observed for aorta and the proximal right coronary artery. The D 0.1cm3 doses were significantly lower for PBS to the whole heart when compared to IMRT. In the left auricle, the superior vena cava, the coronary sinus, the left ventricle and the anterior and inferior wall of the left ventricle, the proximal circumflex artery, the left anterior descending artery (proximal, middle and distal), the left main coronary artery, the right coronary artery (proximal, middle), the D 0.1cm3 was significantly lower for PBS than IMRT.