ESTRO 2020 Abstract Book

S895 ESTRO 2020

Conclusion The defined-filling protocol did not result in a reproducible daily gastric volume, which in consequence could alter adequate coverage of the TVs while increasing doses to OARs. In turn, adaptive radiotherapy significantly improved accuracy on dose coverage and OARs sparing. PO-1635 How do UK centres clinically use, commission, and QA deformable image registration? M. Hussein 1 , J. McClelland 2 , R. Speight 3 , C.H. Clark 1 1 National Physical Laboratory, Centre for Metrology in Medical Physics - MEMPHYS, Teddington, United Kingdom ; 2 University College London, Centre for Medical Image Computing - CMIC, London, United Kingdom ; 3 Leeds Teaching Hospitals NHS Trust, Leeds Cancer Centre, Leeds, United Kingdom Purpose or Objective The use of Deformable Image Registration (DIR) in radiotherapy is gradually being clinically adopted as most commercial TPS vendors now offer some form of DIR. For the commissioning and ongoing QA of DIR, there have until recently been limited guidelines [1]. No national information exists on UK centres are using DIR clinically, which applications are being used, and what commissioning and QA tests are performed. This study aimed to survey UK centres to gather this data and to determine whether additional national guidelines are required. Material and Methods The survey was sent to all 71 UK-based radiotherapy centres. Questions were designed to gather information on the following: which applications are DIR algorithms currently used for in clinical practice and for which anatomical sites, how DIR is being commissioned, what type of commissioning data is used, and what routine QA practice is in place and how frequent. The survey also sought to identify whether further UK-specific guidance may be required. DIR software was defined as software that explicitly performs a deformable registration, and saves the resulting transformation and/or deformed images to be further used for another application. Centres that do not use DIR clinically were encouraged to fill in the survey and were asked if they have any future plans and in what timescale. The survey was opened between January and April 2019. Results In total 50 (70%) centres responded. From these centres, 46 reported access to one of the commercial software that could perform DIR according to our definition. In total, 20 centres indicated that they already use DIR clinically, and a further 22 centres had plans to implement an application of DIR within 1 year of the survey. Table 1 shows a summary of the different applications of DIR in clinical use, including the most common clinical sites, type of commissioning data used and frequency of ongoing QA. The most common clinical application of DIR was to propagate contours from one scan to another (19 centres). Table 1 shows that in all of the applications, patient data and patient-specific QA were most frequently used for commissioning tests and ongoing QA respectively. The types of tests performed varied depending on the type of application, with qualitative tests being more common for ongoing QA. For example, Fig 1 shows the different types of tests used for commissioning and ongoing QA for contour propagation. Specific comments from respondents included the need for improved user-friendliness of QA software, difficulty implementing existing QA recommendations and determining when a deformable registration was satisfactory.

Conclusion The survey highlights that, in the UK, whilst almost all of the responding centres had access to software capable of DIR, only two out of five were using it in routine clinical practice. The results gave useful insight into how centres commission and QA DIR, and will form the basis for developing national guidelines. References [1] Brock et al. Med. Phys. 2017. PO-1636 Robustness of breast treatments with Tomotherapy toward residual setup errors L. Marrazzo 1 , F. Maresca 2 , M. Icro 2,3 , C. Arilli 1 , S. Calusi 2 , M. Casati 1 , A. Compagnucci 1 , C. Talamonti 1,2 , I. Desideri 2 , L. Livi 2,3 , S. Pallotta 1,2 1 Azienda Ospedaliera Universitaria Careggi, Medical Radiation Physics, Firenze, Italy ; 2 University of Florence, Department of Experimental and Clinical Biomedical Sciences “Mario Serio”, Florence, Italy ; 3 Azienda Ospedaliera Universitaria Careggi, Radiation Oncology, Firenze, Italy Purpose or Objective Breast radiotherapy is usually performed with tangential fields (both static and intensity modulated). In particularly challenging anatomies or when axillae level 3-4 (AL3-4) and internal mammary nodes (IMN) have to be treated, the use of rotational techniques generally allows to obtain improved dose distributions. Helical Tomotherapy (HT) can be used for breast treatments, but it does not allow to explicitly account for a skin flash margin. Although daily MVCT is used to correct patient setup at each fraction, it is worthwhile to test the