ESTRO 2025 - Abstract Book

S3075

Physics - Inter-fraction motion management and offline adaptive radiotherapy

ESTRO 2025

151

Digital Poster Quantification of the Patient Positioning with Surface Guided Radiotherapy in Thoracic Malignancies: Comparison with Tattoo-Based Setup Eline A van Rooy 1 , Erik B van Dieren 2 , Judith Dasselaar 2 1 Faculty of Science and Technology, University of Twente, Enschede, Netherlands. 2 Radiotherapy, medisch spectrum twente, Enschede, Netherlands Purpose/Objective: Surface-guided radiotherapy (SGRT) offers advantages over the tattoo-based setup by providing postural information and abandoning the impact of permanent skin marks. This research aims to quantify the benefit of using SGRT for patients with thoracic malignancies, compared to tattoo-based setup. Material/Methods: In our department, Varian’s IDENTIFY TM system is installed on one linear accelerator (Ethos, Varian Medical systems, Palo Alto, USA) and treatment of patients with thoracic malignancies is in IGRT mode. Patients were positioned with the tattoo-based setup on Mondays and Tuesdays, and the SGRT setup on Thursdays and Fridays. Data acquisition lasted for 7 weeks. The translational and rotational data generated after the Cone-Beam CT (CBCT) auto-match were analyzed to compare both setups in the quantification of patient position. Results: In total, 351 fractions and 37 patients were included. 150 fractions positioned with the tattoo-based setup and 124 fractions positioned with SGRT setup could be evaluated (14 lung cancer and 13 esophageal cancer patients). The remaining data were excluded because of field-of-view problems and data export issues. Table 1 provides the mean and standard deviation for all fractions, lung cancer patients and esophageal cancer patients. Figure 1 illustrates the translational and rotational shifts after CBCT auto-match for tattoo-based and SGRT setup. The median numbers of the tattoo-based and SGRT setup are comparable and within the threshold windows. 87% of the fractions for the tattoo-based setup and 90% of the fractions for the SGRT setup were within 0.5 cm of the isocenter. 96% of the tattoo-based setup and 95% of the SGRT setup were within 2 degrees, although the number of outliers varies per rotational axis. The number of fractions within the 2 degrees threshold for yaw, pitch and roll were (95%, 96%, 97%) for the tattoo-based setup versus (94%, 98%, 93%) for the SGRT setup.