ESTRO 2021 Abstract Book

S174

ESTRO 2021

Figure 1. The flowchart of correlation model

Results The mean±standard deviation of the prediction errors of model 1 were 2.99±1.40mm (LR) and 2.58±0.83mm (RF) for centroid, 3.51±2.24mm (LR) and 3.07±1.74mm (RF) for apex in the first fraction; 3.05±0.44mm (LR) and 4.74±0.64mm (RF) for centroid, 3.65±0.36mm (LR) and 5.41±0.11mm (RF) for apex in the second fraction. The average prediction errors of model 2 were 2.85±0.23mm (LR) and 3.36±0.24mm (RF) for centroid, 3.41±0.40mm (LR) and 3.87±0.78mm (RF) for apex in the second fraction. The prediction accuracy of the model 2 is higher than that of the model 1 in second fraction.

Figure 2. A. Motion trajectory of the diaphragm centroid; B. Motion trajectory of the diaphragm apex

Conclusion This study shows that it is feasible to use the optical body surface information to automatically predict the diaphragm motion trajectory with enough accuracy. At the same time, it is necessary to establish a new correlation model for the current fraction before each treatment. This technique can be used to noninvasively manage tumor movement in real time during radiotherapy of liver tumor near the diaphragm. PH-0266 Fast deformable contour propagation for intra-fraction adaptive MR-guided prostate radiotherapy T. Willigenburg 1 , C. Zachiu 1 , J. Lagendijk 1 , H. de Boer 1 , J. van der Voort van Zyp 1 , B. Raaymakers 1 1 University Medical Center Utrecht, Radiation Oncology, Utrecht, The Netherlands Purpose or Objective Intra-fraction (IF) adaptation and full re-planning for ultra-hypofractionated MR-guided prostate cancer (PCa) radiotherapy would allow for offering a completely non-invasive treatment, i.e., without a need for fiducial markers, rectal spacers, and urinary catheters. However, progression towards IF re-planning workflows using repetitive MR imaging is hindered by, among other things, a need for extensive online manual adaptation of the propagated contours. A fast and accurate auto-contouring solution that reduces the need for manual adaptation is needed. Here we assess the clinical usability of IF propagated contours by a deformable image