ESTRO 2020 Abstract book

S839 ESTRO 2020

planning comparison study of robustly planned PBS vs VMAT using cases and treatment planning parameters from the NeoSCOPE trial to establish any potential reductions in lung and heart dose that may reduce the incidence of post- operative pulmonary and cardiac toxicities. Material and Methods We created PBS and VMAT plans for four datasets from NeoSCOPE that had 4DCT-generated ITVs. PBS plans were robustly optimised on ITV (95% coverage) using 5mm setup uncertainty and 3.5% range uncertainty. Gantry angles of 135°, 180° and 225° were used. Second-to-worst ITV coverage were reported. VMAT was optimised to PTV (ITV+5mm margin) with all plans using one full 360° arc. Both plans were optimised using treatment parameters from the NeoSCOPE trial to a dose of 45Gy/25#. Additionally, we reported dose to V5 lung and V40 heart. Treatment planning and dose analysis were done on Pinnacle (Phillips, v14 (PBS) and v16 (VMAT)). Results

Image 1: Typical beam arrangement used (135°, 180° and 225°) Conclusion We selected a three beam arrangement rather than two to improve plan robustness to breathing motion and to reduce the effect of anatomical changes along any one beam path at the expense of greater lung dose. Despite this, PBS still showed significant dosimetric advantage in most parameters with acceptable coverage of ITV. Lung V5 is shown to be an independent dosimetric factor in multivariate analysis in reducing the incidence of post- operative pulmonary complications. This study shows lung V5 reduction of over 50% in all 4 cases. Similiarly, both DVH parameters (V40, V25) for heart dose showed a significant reduction which may lower the incidence of post-operative cardiac toxicity. Further considerations will be required during treatment delivery to account for intra/inter- fraction tumour motion, breathing motion and interplay effects. This study indicates that delivering NACRT with PBS for oesophageal cancer may lead to a meaningful reduction in post-op pulmonary and cardiac toxicity. However, there remains a paucity of published clinical data for PBS in this setting. We recommend that NACRT with PBS for distal oesophageal cancer is tested prospectively in a randomised controlled trial. PO-1472 Cardiac dose reduction in proton vs. photon DIBH breast and regional lymph nodes radiotherapy P. Winczura 1 , K. Czerska 2 , J. Wejs-Maternik 3 , A. Blukis 3 , R. Mężykowski 3 , P. Olko 4 , R. Kopeć 2 , A. Badzio 5 1 Radiotherapy Center Elblag, Departent of Radiotherapy, Elblag, Poland ; 2 Institute of Nuclear Physics PAN, Cyclotron Centre Bronowice, Kraków, Poland ; 3 Radiotherapy Center Elblag, Radiotherapy, Elblag, Poland ; 4 Institute of Nuclear Physics PAN, Proton Radiotherapy Group, Kraków, Poland ; 5 Medical University of Gdańsk, Department of Oncology and Radiotherapy, Gdańsk, Poland Purpose or Objective Deep inspiration breath-hold (DIBH) is an effective and widely used technique to reduce the dose to the critical structures in left-sided breast cancer radiotherapy. In this study we compared photon Intensity Modulated Radiation Therapy (IMRT) versus Intensity Modulated Proton Radiotherapy (IMPT) with deep inspiration breath hold (DIBH) and free breathing (FB) on dose reduction to the heart and left anterior descending coronary artery (LAD). Material and Methods Five patients with left-sided breast cancer were planned on DIBH and FB computed tomography datasets. For each patient 6MV photon IMRT and proton IMPT with 2 or 3 fields plans were created. Patients were planned to the CTV which consisted of the left breast and regional lymph nodes: axilla level 1-3 and supraclavicular region. Contouring was performed according to the ESTRO

Data Table: Results of dose comparison between PBS and VMAT