ESTRO 2020 Abstract book

S236 ESTRO 2020

United Kingdom ; 3 Ingham Institute for Applied Medical Research, Liverpool Cancer Therapy Centre, Sydney, Australia ; 4 Guy’s and St. Thomas’ NHS Foundation Trust and University College London, Dept. of Computer Science, London, United Kingdom ; 5 The Christie NHS Foundation Trust and the University of Manchester, Radiotherapy, Manchester, United Kingdom ; 6 The Christie NHS Foundation Trust and the University of Manchester, Medical Physics and Engineering, Manchester, United Kingdom ; 7 University of Oxford, Department of Oncology, Oxford, United Kingdom ; 8 Umeå University, Department of radiation sciences, Umeå, Sweden ; 9 Odense University Hospital and University of Southern Denmark, Laboratory of Radiation Physics, Odense, Denmark ; 10 Kymenlaakso Central Hospital, Department of Medical Imaging and Radiation Therapy, Kotka, Finland ; 11 Auckland Radiation Oncology, Epsom, Auckland, New Zealand ; 12 University Medical Center Utrecht, Department of Radiotherapy, Utrecht, The Netherlands ; 13 Ghent University Hospital, Department of Radiation Oncology, Ghent, Belgium ; 14 AOU Careggi Firenze University Hospital, Department of Health Physics, Firenze, Italy ; 15 Centre Oscar Lambret, Department of Medical Physics, Lille, France ; 16 Northern Centre for Cancer Care, Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, United Kingdom Purpose or Objective Despite growing interest in MRI, integration in external beam radiotherapy (EBRT) treatment planning uptake varies globally. In order to understand the current international landscape of MRI in EBRT a survey has been performed in 10 countries. This work reports on differences and common themes identified. Material and Methods A survey was developed covering eight topics: MRI access; MRI use; MRI to CT registration; commissioning/Quality Assurance (QA); safety; workflow/staffing; education; and future applications. The survey was distributed within 10 countries by a ‘local champion’ ensuring it reached all radiotherapy centres. Results The survey had a median response rate of 77% per country (184/442 in total). Response rates in individual countries varied between those with high response rates (≥66% in the UK/Denmark (DK)/Finland (FN)/Sweden (SE)/Netherlands (NL)/Belgium (BE)/New Zealand (NZ)) and those with response rates low enough that results cannot be considered representative of the country (≤35% in Italy (IT)/France (FR)/Australia (AU)). MRI access was varied between countries, with FR and the UK reporting the lowest rates (43% and 69% respectively). In DK/SE >80% of centres reported having dedicated MRI scanners for EBRT, whereas in all other countries <25% reported dedicated scanners for EBRT and were more reliant on collaboration with radiology for MRI access. Anatomical sites receiving MRI for EBRT varies internationally and the most common are shown in table 1. Commissioning and QA of both image registration and MRI scanners varied greatly, as did MRI sequences performed, staffing models and training given to different staff groups.

The most common barrier for increasing MRI scans for radiotherapy across all centres (figure 1) was MRI access and a lack of financial reimbursement, except DK/SE where lack of clinical interest/local knowledge was the main barrier.

It was reported that within 5 years a median of 29% (range 9-50%, absolute number 57) of centres per country are planning for a new MRI scanner dedicated for EBRT A limited number of sites in NL/DK/SE/FN/AU/BE currently employ MRI-only EBRT planning; over the next 5 years MRI- only EBRT planning is expected to be taken up in >50% of centres in NL/SE/DK/FN but < 35% in UK/NZ/BE/FR/AU/IT. MR-linac technology is being clinically employed in DK/UK/NL and within 5 years expected uptake varies between 63% in DK, 59% in NL and <35% in UK/FN/SE/NZ/BE/AU/IT/FR. Conclusion The current international use of MRI for EBRT has been surveyed in 10 countries. Variations in practice/equipment/QA/staffing models have been identified. These are likely due to differences in funding as well as a lack of consensus or guidelines in the literature. For most countries the lack of MRI access and funding is the limiting factor on the number of patients who benefit from MRI as part of their EBRT treatment planning. Despite these challenges, significant interest remains in increasing MRI-assisted EBRT planning over the next 5 years. PH-0407 Tumour-site specific geometric distortions in high field MR-Linac treatments S.W. Hasler 1,2 , E. Van Veldhuizen 1,2 , A. Bertelsen 1,2 , U. Bernchou 1,2,3 , T. Schytte 1,2,3 , V.N. Hansen 1,2 , C. Brink 1,2,3 , F. Mahmood 1,2,3 1 Odense University Hospital, Department of Oncology, Odense, Denmark ; 2 Odense University Hospital, Laboratory of Radiation Physics, Odense, Denmark ; 3 University of Southern Denmark, Department of Clinical Research, Odense, Denmark Purpose or Objective MRI-guided radiotherapy (RT) enables superior soft-tissue outlining of both target and organs at risk. However, geometric distortions in MR images warrant caution in MRI- guided treatment planning. The MRI-system related B 0 non-uniformity and gradient non-linearity (GNL), and patient (pt) induced B 0 disturbance are the main contributors to the total geometric distortion. Further,