ESTRO 2022 - Abstract Book

S1505

Abstract book

ESTRO 2022

A total of 62 MR frames was analysed, considering a TCV of 50% as threshold to switch off the beam. TCV is an estimation of the similarity of continuos frames. Results Multi-imaging modalities evaluation (figure 1) confirms previous studies, showing the suitability to use the fiducial marker in orthogonal kV, CBCT and CT. Small artifacts (negligible for contouring aims) were observed in the CT and CBCT image dataset. MR TRUFI images reveal for the very first time, optimal marker spatial resolution, appearing as an hypointense spot. Selection of the in-plane voxel sizes could obviously affect the results. When rigidly fused, CT and MRI images show an excellent matching of the markers.

TCVs highlight the dependency of the marker size and the surrounding medium contrast, as shown in figure 2. Concerning the vial containing minced beef, the lowest mean (over the 62 images) TCV was 32.4% (marker size of 0.10 ml). Fiducial marker of 0.20 ml has an higher mean TCV (48.6%) but with bigger variability (standard deviation of 17.1%). On the other hand, fiducial marker of 0.30 ml shows a TCV over the 50%. All the fiducial markers (0.1 ml, 0.2 ml and 0.3 ml) contained in the hand gel vial present a tracking confidence value always higher than 58.2%.

Conclusion The evaluated fiducial marker can be employed in the MRgRT system, providing an adequate spatial accuracy for the volumetric 3D MR TRUFI image as well as for cine MR gating purposes. Clinical use of the markers for patients affected by liver cancer is under scheduling.

PO-1706 Designing a national end-to-end audit for respiratory motion management

A. Burton 1 , S. Beveridge 1 , N. Hardcastle 2 , J. Lye 3 , M. Sanagou 4 , R. Franich 5