ESTRO 2025 - Abstract Book

S3222

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

ESTRO 2025

1263

Digital Poster SGRT analysis of patient and tumor motion/position during adaptive radiotherapy Fernanda Macedo-Jimenez, Jens Fleckenstein, Iris Kalisch, Frank A. Giordano, Florian Stieler Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Mannheim, Germany Purpose/Objective: Modern radiation therapy (RT) relies on precise patient positioning via image-guided RT. Surface-guided RT (SGRT) enables inter- and intra-fractional motion management without additional imaging dose. The recently introduced adaptive RT (ART) allows real-time treatment plan adjustments based on daily anatomical changes, but involves an extensive, time-consuming workflow. This work retrospectively analyses intra-fractional patient motion using SGRT during ART for prostate cancer. Furthermore, we assess the relation between CBCT internal target position and SGRT surface position for prostate cancer. Material/Methods: Thirty prostate cancer patients treated with ART on Varian Ethos and SBRT using a ring-mounted SGRT (inBore, Vision RT) system were retrospectively analysed (138 fractions in total). The mean and standard deviation values of the surface motion during the treatment time of up to 60 minutes on the three translational axes were calculated. Translational CBCT shifts of the second daily CBCT directly before RT and surface position data were analysed to determine the agreement between SGRT and CBCT for intra-fractional position of deep-located tumors. Relations between CBCT shifts and SGRT data were assessed with the Wilcoxon paired samples test. Results: The maximum mean (±SD) surface motion values during the first 45 minutes of treatment were -2.21±1.27 mm on the vertical (VRT) axis at 45-min as illustrated in Figure 1, 0.36±2.17 mm on the longitudinal (LNG) axis at 35-min, and 0.14 mm±1.13 mm on the lateral (LAT) axis at 45-min. The mean (±SD) surface position deviations after the translational CBCT shift can be visualized in Figure 2, with -0.66±1.42 mm (VRT), - 0.24±1.62 mm (LNG), and 0.05±0.86 mm (LAT), and ranges of 8.3 mm, 10.02 mm, and 6.08 mm on the VRT, LNG, and LAT axes, respectively. Statistical analysis indicated a significant difference (p<0.05) between the paired samples of position data from the CBCT shift and SGRT on the vertical and longitudinal axes, with no significant deviation on the lateral axis.

Figure 1. Vertical (VRT) mean and SD surface motion during ART combined with SBRT for prostate cancer.