ESTRO 2021 Abstract Book

S176

ESTRO 2021

feasible for the identification of voxels with continuous low motion (e.g. bowel adhesion), whereas voxels with discontinuous high motion were more susceptible for any errors. The M50% of the median and max95% motion showed an average of 1.6 mm/dynamic (range 0.6-3.2 mm/dynamic) and 5.1 mm/dynamic (range 2.0- 8.7 mm/dynamic), respectively (Figure 2).

Conclusion A median motion metric is the best option to visualize and quantify bowel motion using DIR in a 3D cine-MRI acquisition. The max95% motion metric may be used to identify regions of minimal motion inside the high-dose area, which are of interest in treatment planning. PH-0268 Precision of image-guided RT for spinal SABR patients and impact of positioning variables C. Billiet 1 , S. Van Laere 2 , I. Joye 1 , C. Mercier 1 , P. Dirix 1 , W. Vingerhoed 3 , P. Vermeulen 4 , D. Nevens 1 , P. Meijnders 1 , D. Verellen 1 1 Iridium Netwerk; Center for Oncological Research (CORE), Integrated Personalized and Precision Oncology Network (IPPON), University of Antwerp., Radiation Oncology, Antwerp, Belgium; 2 University of Antwerp; GZA Hospitals, Center for Oncological Research (CORE); Translational Cancer Research Unit, Antwerp,