S2243
Physics - Intra-fraction motion management and real-time adaptive radiotherapy
ESTRO 2026
differences were minimal across strategies (<0.30% for pneumonitis; <1.00% for rib fractures), indicating negligible clinical impact. The in-bunker evaluation was limited by the system’s gun hold time (GHT), which prevented successful delivery of gated treatments for all respiratory signals analyzed within the clinically relevant frequency range of 0.15–0.50 Hz.
Digital Poster 3057
Comparing Dosimetric Performances of Inspiration/Expiration Gating Versus Free
Breathing in Lung SBRT: A Pre-Clinical Evaluation Silvia Cereda 1,2 , Valeria Faccenda 2,3 , Riccardo Ray Colciago 3 , Martina Scotti 1,2 , Stefano Arcangeli 3,4 , Denis Panizza 2,3 , Elena De Ponti 2,3 1 Physics, University of Milan, Milan, Italy. 2 Medical Physics, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy. 3 School of Medicine and Surgery, University of Milan Bicocca, Milan, Italy. 4 Radiation Oncology, Fondazione IRCCS San Gerardo dei Tintori, Monza, Italy Purpose/Objective: Stereotactic body radiotherapy (SBRT) for lung tumors is challenged by respiratory-induced motion, which can compromise target coverage and organ-at-risk (OAR) sparing. Among motion management strategies, respiratory gating has the potential to reduce treatment margins while allowing normal breathing. However, its dosimetric superiority over conventional free-breathing (FB) planning remains unclear, and the optimal gating phase (inspiration vs. expiration) is still debated. Moreover, beam-on latency poses a key technical limitation. This study aimed to compare the dosimetric performance of inspiration- and expiration- gated SBRT with FB plans, and to experimentally assess the feasibility of gated delivery using a clinical linear accelerator integrated with surface-guided radiation therapy (SGRT). Material/Methods: A retrospective in silico analysis was performed on 20 patients with non-small cell lung cancer (NSCLC) or pulmonary metastases eligible for SBRT. For each patient, ITV-based FB, inspiration-gated, and expiration-gated plans were generated. Dosimetric parameters for targets and OARs were compared, and the impact of tumor motion, ITV, and lung volume on lung dosimetry was assessed. Plan quality indices were also compared, and percentage differences in normal tissue complication probability (NTCP) for lung pneumonitis and symptomatic rib fracture were evaluated. An in-bunker experimental study on an Elekta VersaHD linac using a dynamic respiratory phantom reproducing actual respiratory patterns and SGRT-based gating was conducted to evaluate gated delivery feasibility. Results: Both inspiration- and expiration-gated plans showed significant ITV reduction and improved OAR sparing compared with FB gradients (p<0.035), while proving essentially equivalent to each other. ITV reduction emerged as the strongest predictor of dosimetric improvements (R ² >0.50). FB plans showed better conformity and gradients (p<0.009), and NTCP
Conclusion: Dosimetric comparison between inspiration- and expiration-gated plans revealed similar tumor and OAR doses. Although gated plans showed modest dosimetric improvements over FB, NTCP analysis showed no clinically relevant benefit. Experimental validation highlighted technical limitations that challenge the practical implementation of gating.Overall, these findings do not support the routine clinical adoption of respiratory gating for lung SBRT. Keywords: Respiratory gating, Tumor motion management
Made with FlippingBook - Share PDF online