ESTRO 2025 - Abstract Book

S3334

Physics - Intra-fraction motion management and real-time adaptive radiotherapy

ESTRO 2025

during treatment delivery perpendicular to the treatment beam. Post-treatment, the fiducial markers were segmented in each kV image using an automatic template-based segmentation algorithm followed by manual inspection and semiautomatic correction of failed segmentations. The 2D marker positions in each kV image were used to determine the 3D marker motion in patient coordinates during treatment by a probability-based method. For all monitored fields, the intra-field drift motion from the first 3s to the last 3s of the field delivery and the mean LN position error relative to the planned position were determined (Figure 1).

Results:

The intra-field drift motion and position error for each patient in each direction are shown as box plots in Figure 2. Averaged over all the patients the intra-field LN drift motion was 0.4±0.9 mm (LR), 2.5±1.9 mm (CC), and -0.2±1.5 mm (AP), and it exceeded 4mm in 4.8% (LR), 20% (CC) and 5.8% (AP) of the field deliveries. The mean LN position error during field delivery was 1.2±6.3 mm (LR), 3.3±4.9 mm (CC), and 1.7±2.6 mm (AP) and exceeded 10 mm in 13.8% (LR), 25% (CC) and 4.8% (AP) of the field deliveries.