ESTRO 2021 Abstract Book

S1455

ESTRO 2021

Results The deviations between the six degree-of-freedom (6DoF) couch shifts and the shift trackings in AlignRT were sub-millimeter and sub-degree, and no drift over 1 mm or 1 degree were identified. The ROI mode of isocenter (ISO) exhibited more consistent results than centroid (CEN). The isocenter discrepancies between CBCT and other imaging modalities were investigated: the isocenter discrepancy of kV-kV was negligible; the maximal isocenter discrepancies of MV-MV were 0.4 mm in LNG and 0.3 degree in PITCH; the isocenter discrepancies of AlignRT were < 0.5 mm in translation and < 0.3 degree in rotation. Also, for AlignRT, the isocenter discrepancies between the DICOM and SGRT references were about 0.6 mm in VRT, 0.5 mm in LNG and 0.2 degree in PITCH. The time required to complete the QA procedure was around 23 minutes. Conclusion The streamlined QA procedure exhibits desirable practicability as an efficient multiple-purpose performance check on positioning guidance systems. The tracking performance and isocenter congruence of the positioning guidance systems have been fully validated for clinical SRS application. PO-1732 IPEM Guidelines on the use of MRI for external beam radiotherapy treatment planning R. Speight 1 , M. Dubec 2 , C. Eccles 2 , B. George 3 , A. Henry 4 , T. Herbert 5 , R. Johnstone 6 , G. Liney 7 , H. McCallum 8 , M. Schmidt 9 1 Leeds Teaching Hospitals NHS Trust, Leeds Cancer Centre, Leeds, United Kingdom; 2 The Christie NHS Foundation Trust and the University of Manchester, -, Manchester, United Kingdom; 3 University of Oxford and GenesisCare, -, Oxford, United Kingdom; 4 Leeds Cancer Centre, Leeds Teaching Hospitals NHS Trust and University of Leeds, -, LEEDS, United Kingdom; 5 Royal Marsden NHS Foundation Trust, -, London, United Kingdom; 6 Guy’s and St. Thomas’ NHS Foundation Trust, -, London, United Kingdom; 7 Ingham Institute for Applied Medical Research and Liverpool Cancer Therapy Centre, -, Sydney, Australia; 8 Translational and Clinical Research Institute, Newcastle University and Northern Centre for Cancer Care, Newcastle upon Tyne Hospitals NHS Foundation Trust, -, Newcastle upon Tyne, United Kingdom; 9 Royal Marsden NHS Foundation Trust and Institute of Cancer Research, -, London, United Kingdom Purpose or Objective The role of MRI to guide external beam radiotherapy (RT) treatment planning is growing. The literature shows significant heterogeneity in the way that MRI for RT is implemented and there is some evidence that this is, in part, due to a lack of consensus in the literature and guidance from professional bodies [1-2]. To combat this, The Institute of Physics and Engineering in Medicine (IPEM) commissioned a working party to produce a guidance document on the use of MRI for RT treatment planning. This guidance has now been published [3] and its key findings will be discussed in this abstract. Materials and Methods The guidelines were produced by a multi-disciplinary party consists of 10 members which first met in February 2018. The guidance is based on the experience of the institutions represented in the IPEM working party, in consultation with other institutions, as well as information taken from the literature. It has multi-disciplinary endorsement from the professional bodies IPEM, Royal College of Radiologists (RCR) and the Society of Radiographers (SCoR). Guidance is only given for MRI acquired for external beam RT treatment planning in a CT-based workflow, i.e. when MRI is acquired and registered to CT with the purpose of aiding delineation of target or organ at risk volumes. MRI use for treatment response assessment, MRI-only RT and other RT treatment types such as brachytherapy, gamma radiosurgery and MR linac are not considered within the scope of this document. Results The guidelines are designed to be a practical document which can benefit all involved disciplines and give advice on introducing an RT workload onto a non-RT-dedicated MR scanner, as well as planning for installation of an MR scanner dedicated for RT (sometimes referred to as an MR-sim). Practical guidance is given on the following, in the context of RT planning: safety; training and education for all staff working in and around an MR scanner; RT patient set-up on an MR scanner; MRI sequence optimisation for RT purposes; commissioning and quality assurance (QA) to be performed on an MR scanner; and MRI to CT registration, including commissioning and QA. Conclusion For the first time a guidance document has been produced on the use of MR in external beam radiotherapy treatment planning. This has been produced by a multidisciplinary team and is endorsed by multiple professional bodies. It is hoped that this document will aid in the safe implementation of MRI for external beam radiotherapy treatment planning both for centres with dedicated MR scanners for radiotherapy and for centres with MR access for radiotherapy on scanners owned by radiology. Furthermore, it is hoped that this