ESTRO 2020 Abstract book

S175 ESTRO 2020

adaption was used in 50% of the centres, mainly for head and neck cancer; however, online or offline ART protocols were only used in 31% of the centres. CBCT/MVCT was the main imaging modality used for adaption (Fig. a). Of the 11 centres using online daily replanning, one used CT while others used MR. Three centres reported “poor mask fitting” as a reason for head and neck ad-hoc adaption. Pre-treatment phantom measurements and secondary dose calculations were the most common QA methods (>50% of centres using ART). EPID/ in vivo dosimetry, log files and post-treatment phantom measurements were used in 21%, 16% and 11% of centres respectively. While 92% of centres used commercial software, 19% of centres used (also) in-house software due to lack of functionalities and/or cost. Figure b shows the state and wishes for ART implementation and further use. Two thirds of centres wished to implement ART for a new tumor site, of which 40% have plans to do it in the next 2 years (Fig. c). Human/financial resources and technical limitations were reported as the main barriers while reimbursement was considered a minor hindrance (Fig. d-e).

PD-0311 Patterns of practice for adaptive and real-time radiation therapy part II: interfractional changes J. Bertholet 1 , G. Distefano 2 , D. Noble 3 , A. Bel 4 , R. VanLeeuwen 5 , T. Roggen 6 , M. Duchateau 7 , S. Thørnqvist 8 , C. Garibaldi 9 , N. Tilly 10 , R. Garica Mollá 11 , J. Bonaque 12 , U. Oelfke 1 , M. Aznar 13 , B. Heijmen 14 1 The Institute of Cancer Research and the Royal Marsden Hospital NHS Foundation Trust, Joint Department of Physics, London, United Kingdom ; 2 Royal Surrey County Hospital, Medical physics, Guildford, United Kingdom ; 3 University of Cambridge and Addenbrooke’s Hospital, Cancer Research UK VoxTox Research Group- Department of Oncology, Oxford, United Kingdom ; 4 Amsterdam UMC, department of Oncology, Amsterdam, The Netherlands ; 5 Radboud university medical center, department of Radiation Oncology, Nijmegen, The Netherlands ; 6 Varian Medical Systems Imaging Laboratory GmbH, Applied research, Dättwil AG, Switzerland ; 7 MIM software Inc, n/a, Cleveland, USA ; 8 Haukeland University Hospital, Department of oncology and medical physics, Bergen, Norway ; 9 IEO- European Institute of Oncology, Unit of Radiation Research, Milano, Italy ; 10 Unppsala University and Elekta Instruments AB, Department of Immunology- Genetics and Pathology, Uppsala and Stockholm, Sweden ; 11 Consorcio Hospital General Universitario de Valencia, Servicio de Radiofísica y Protección Radiológica, Valencia, Spain ; 12 Consorcio Hospitalario Provincial de Castellón, Servicio de Radiofísica y Protección Radiológica, Castelló, Spain ; 13 University of Manchester, Division of Cancer Sciences- School of Medical Sciences, Manchester, United Kingdom ; 14 Erasmus MC Cancer Institute, Department of Radiation Oncology, Rotterdam, The Netherlands Purpose or Objective The patterns of practice for adaptive and real-time radiotherapy (POP-ART RT) study aims to determine to what extent and how these methods are used in clinical practice and to understand the barriers to implementation. Here we report on part II: ART to address interfractional anatomical changes. Material and Methods An institution-specific questionnaire developed during the 2 nd ESTRO physics workshop was distributed worldwide. The focus was both on current practice and wishes for implementation. Therefore, centres not doing ART were encouraged to participate. ART was defined as the use of more than one plan per target per treatment course to counteract the negative dosimetric impact of interfractional anatomical changes using: 1) online daily replanning 2) online plan libraries 3) offline protocols (action levels or scheduled surveillance scans) or 4) offline adaption ad-hoc (e.g. due to weight loss). Respondents were asked if and which type of ART was used in their centre for selected tumor sites, which imaging modality was used to guide adaption (more than one response possible), what type of quality assurance (QA) was performed on the adapted plan (more than one response possible) and what type of software was used for the adaptive procedure. Respondents were asked if they wished 1) to change/expand their use of ART for sites already treated using ART or 2) implement ART for new tumor site(s) and to rank barriers to implementation in order of importance. Results The questionnaire was filled out by 177 centres from 40 countries. The percentages of centres using ART for selected sites are shown in Table 1. Offline ad-hoc