S2260
Physics - Intra-fraction motion management and real-time adaptive radiotherapy
ESTRO 2026
Hospital Clínic, Barcelona, Spain. 3 Department of Medicine, Universitat de Barcelona, Barcelona, Spain
Purpose/Objective: Although Deep Inspiration Breath Hold (DIBH) is widely adopted to minimize cardiac dose in left-sided breast cancer, intra and inter fraction changes in breath-hold (BH) quality during treatment have not been systematically analysed. This work quantifies session-to-session changes in DIBH stability, reproducibility, and efficiency to detect self-training effects. Material/Methods: A retrospective analysis was performed on 10 left- sided breast cancer patients treated with DIBH using Varian Real-time Position Management (RPM) system. For each session, respiratory curves were analysed (Figure 1) to extract quantitative parameters describing BH quality, stability, and temporal performance. The metrics included:BH Effectiveness (BHef): ratio between successful BH to total attempts. A succesful BH was defined as a BH equal or longer than 15 seconds.Mean BH amplitude per session (BHA).Standard deviation from BHA (BH σ )BH coefficient of variation (BHCV)Total treatment time (TTT)Mean BH Time (BHT).Treatment was divided in two stages. Initial (first 5 sessions), rest (remaining sessions). Each metric was compared across stages using Wilcoxon signed-rank test.
Conclusion: To conclude, this study analysed motion signatures of the diaphragm, chest wall, and an internal vessel, along with regional lung expansion patterns derived from Jacobian determinant matrices. Diaphragmatic and internal vessel motion were significantly reduced in the upright posture, while chest-wall motion remained similar for both postures. The internal vessel motion was less variable in the upright posture as well. These findings support the feasibility of accurate respiratory motion management and tumour targeting for upright thoracic radiotherapy. Inter-individual variability, rather than posture, appeared to dominate regional lung expansion and contraction patterns. References: [1] Volz, L., Korte, J., Martire, M. C., Zhang, Y., Hardcastle, N., Durante, M., Kron, T., & Graeff, C. (2024). Opportunities and challenges of upright patient positioning in radiotherapy. Physics in Medicine and Biology, 69(18). Keywords: Lung Cine MR, Motion Analysis, Upright RT Poster Discussion 3933 Evolution of Deep Inspiration Breath-Hold (DIBH) performance during treatment Mario Dorado 1 , Maria del Carmen Muñoz-García 2 , Rita Gasol-Cos 1 , Alvaro Martínez 2 , Maria Laplana 2 , Gabriela Oses 2,3 , Carlos Clavell 2 , Meritxell Mollà 2,3 , Carla Cases 2 1 Faculty of Physics, Universitat de Barcelona, Barcelona, Spain. 2 Department of Radiation Oncology,
Results: Most parameters showed progressive improvement during the treatment course, indicating patient adaptation (Figure2). BHef increased by more than 24%. BH σ and BHCV both significantly decreased by 29% (p < 0.05) showing improvements over BH
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