ESTRO 2025 - Abstract Book

S3264

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

ESTRO 2025

2540

Digital Poster On the correlation of online surface-guided positioning and IGRT of intra-cranial SRS Caisa Kjellström 1,2 , Tobias Pommer 2 , Peter Siesjö 3 , Sofie Ceberg 1 , Per Munck as Rosenschöld 2,1 1 Medical Radiation Physics, Lund University, Lund, Sweden. 2 Radiation Physics, Department of Hematology, Oncology, and Radiation Physics, Skåne University Hospital, Lund, Sweden. 3 Department of Neurosurgery and Section of Neurosurgery, Department of Clinical Sciences, Lund University and Skåne University Hospital, Lund, Sweden Purpose/Objective: Intra-cranial Stereotactic Radiosurgery (SRS) provides high probability of local control but introduces a risk of complications, such as radiation induced brain necrosis (RN) that may cause cerebral oedema. High treatment accuracy is crucial to reduce the risk of RN, this can potentially be achieved using real-time motion monitoring. Recent advances include combining Surface Guided Radiotherapy (SGRT) with stereoscopic Image Guided Radiotherapy (IGRT). In the current study, we investigated the utility and accuracy of a fully integrated SGRT and IGRT system in a large SRS cohort. Specifically, we wish to explore (1) the agreement between the SGRT and IGRT, and (2) the benefit of intra-fractional SGRT and IGRT on treatment accuracy. Material/Methods: A total of 127 SRS patients, with 1-7 (median: 1) intra-cranial targets treated with SRS to 30 Gy in 3 fractions (brain metastases n =118) or 12 Gy in 1 fraction (Schwannoma n =9) were retrospectively analysed. All patients were monitored with ExacTrac Dynamic 1.1 (BrainLab, Munich, Germany), using tolerances of 0.5 mm (degrees) and 1.0 mm (degrees) for translational (rotational) vector deviations for IGRT and SGRT, respectively. For each intrafractional image taken during treatment, the image patient position was paired with a surface position recorded the same moment. The positioning difference between these were then calculated. The imaging frequency simulations computed on the data were modelled after three scenarios: (1) SGRT + IntraArc IGRT, where SGRT was combined with IGRT during treatment delivery and between couch rotations; (2) SGRT + InterArc IGRT, where IGRT was used only between couch rotations; and (3) SGRT only, without additional IGRT after setup. The simulations were performed using Python (3.12). Results: The 95% range for patient positions are in range of -0.44 mm to 0.41 mm (see Figure 1). Spearman’s Rank Correlation (α=0.05) reveals statistically significant correlation between IGRT and SGRT position in all directions ( rho coefficient: 0.44-0.66, p<0.001). Median patient position per treatment beam (see Figure 2) differed between the models (α<0.05). Despite there being a statistical difference between SGRT + IntraArc IGRT and SGRT + InterArc IGRT models, their distributions overlapped visually.