ESTRO 2021 Abstract Book

S132

ESTRO 2021

OC-0202 Influence of deformable propagated structures for lung cancer online daily adaptive proton therapy L. Nenoff 1,2 , M. Matter 1,2 , E.J. Amaya 1 , M. Josipovic 3 , A. Knopf 4 , T. Lomax 1,2 , G.F. Persson 5,6,3 , C.O. Ribeiro 4 , S. Visser 7 , M. Walser 1 , D.C. Weber 8,9,10 , Y. Zhang 1 , F. Albertini 1 1 Paul Scherrer Institute, Center for Proton Therapy, Villigen PSI, Switzerland; 2 ETH Zürich, Department of Physics, Zürich, Switzerland; 3 Rigshospitalet Copenhagen University Hospital, Department of Oncology, Copenhagen, Denmark; 4 University Medical Center Groningen, University of Groningen, Department of Radiation Oncology, Groningen, The Netherlands; 5 Herlev-Gentofte Hospital Copenhagen University Hospital, Department of Oncology, Copenhagen, Denmark; 6 Faculty of Medical Sciences, University of Copenhagen, Department of Clinical Medicine, Copenhagen, Denmark; 7 University Medical Center Groningen, University of Groningen, Department of Radiation Oncology, , Groningen, The Netherlands; 8 Paul Scherrer Institute, Center for Proton Therapy, Viligen PSI, Switzerland; 9 University Hospital Zurich, Department of Radiation Oncology, Zürich, Switzerland; 10 University Hospital Bern, Department of Radiation Oncology, Bern, Switzerland Purpose or Objective Online daily adaptive proton therapy (DAPT) has the potential to improve the treatment quality for various indications, including lung cancer [1, 2]. However, the time and resources needed to re-define or correct the propagated contours is a major limitation and prevents a clinical integration of DAPT so far. In this study, the dosimetric impact of neglecting the online correction of the propagated contours in a DAPT workflow is investigated. Materials and Methods For five non-small cell lung cancer patients with nine repeated CTs, proton therapy plans were optimised on the planning CT to deliver 60 Gy-RBE in 30 fractions. All repeated CTs were first rigidly aligned and then deformed to the planning CT, using six different clinically used deformable image registration (DIR) algorithms. Structures were propagated with each DIR algorithm and reference structures were contoured by a radiation oncologist on each repeated CT and were used to evaluate the dose distribution. DAPT plans were optimised based on the uncorrected, propagated structures ( propagated DAPT doses ) and on the reference structures ( ideal DAPT doses ). Non-adapted doses were recalculated on all repeated CTs. A scheme of the workflow is given in Fig.1. CTV V95, D2 and lung V20 of the propagated DAPT doses and the non-adapted doses were compared to the ideal DAPT doses .