ESTRO 2025 - Abstract Book

S4332

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

1149

Digital Poster agreement between 4D-CT and data-driven 18F-FDG-PET respiratory gating for radiotherapy planning Pooneh Porrangi 1,2 , Adrian Moreno Moreno 3 1 Strålbehandling, Akademiska sjukhuset, Uppsala, Sweden. 2 Department of Immunology, Genetics, and Pathology, Uppsala university, Uppsala, Sweden. 3 Bild- och funktionsmedicinskt centrum, Akademiska sjukhuset, Uppsala, Sweden Purpose/Objective: The main goal of this study is to assess the agreement between data-driven respiratory gating (MotionFree, GE Healthcare) for PET and surface scanning CT gating (Sentinel, C-RAD). This evaluation involved comparing the spatial alignment of corresponding points identified within the target region of both the 4D-CT and MotionFree PET corrected images throughout a simulated respiratory cycle. Aiming to enhance the accuracy of radiotherapy planning for lung cancer patients. Material/Methods: A phantom study compared two respiratory motion compensation technologies: the data-driven MotionFree system for PET, which derives respiratory waveforms from coincidence data, and 4D-CT gating using C-RAD Sentinel's surface-tracking technology. Using a breathing phantom (4-second cycle, 2-cm amplitude) with 18F-FDG, images were analyzed across ten respiratory phases (5-95%).Quantitative analysis evaluated respiratory-associated artifacts, tumor delineation accuracy, and PET/CT spatial alignment. Spatial coordinates (x,y,z) were tracked in both PET and CT images at each respiratory phase to evaluate motion correlation between modalities. Results: The phantom accurately replicated the target breathing pattern (1.89 ± 0.06 cm amplitude). PET images showed optimal tumor definition during mid-respiratory phases (35-65%), with elongation artifacts observed at 15%, 25%, 75%, and 85% phases. Tumor borders appeared indistinct at extreme phases (5%, 95%). PET/CT fusion demonstrated good overall concordance, with localized misalignments primarily at 15% and 85% phases. Motion analysis revealed strong agreement between CT and PET except during rapid motion phases, where CT showed temporal resolution limitations. PET provided superior source movement visualization during these rapid transitions, suggesting complementary strengths of both modalities (showed in Figure 1)

Figure 1 Fused PET/CT images of the respiratory-gated phantom, with color overlay indicating areas of concordance (gray) and mismatch (red) between PET and CT data.