Evaluation of Multi-System Respiratory Surrogate Synchronization and Equivalence for 4D Motion Management In Particle Therapy
Abstract
Purpose
4D motion management in particle therapy requires accurate and reproducible respiratory surrogate signals. The Anzai pressure belt and optical tracking systems are used for respiratory motion monitoring; however, temporal synchronization and spatial agreement among monitoring modalities remain insufficiently quantified. This study introduces the NDI optical navigation system as an optical tracking modality, evaluating temporal synchronization and spatial agreement among respiratory surrogates using a controlled phantom setup.
Methods
Experiments were performed on an Anzai respiratory phantom under controlled breathing conditions at 10 and 15 rpm, including regular periodic motion and physiologic-like asymmetric respiratory patterns. Respiratory signals were acquired using an Anzai belt, an optical tracking system (OTS), and an optical navigation system (NDI) with reflective markers. Temporal synchronization was evaluated using normalized waveform comparison and Pearson correlation analysis. Spatial agreement between NDI and OTS was quantified using the root mean square error (RMSE) of signed three-dimensional displacement, with a 1.0 mm threshold as a clinically relevant benchmark.
Results
Strong temporal synchronization was observed among Anzai, NDI, and OTS signals, with Pearson correlation coefficients ranging from 0.9990 to 0.9998. Waveform morphology and respiratory phase were consistent across cycles. Spatial comparison between NDI and OTS demonstrated sub-millimeter agreement, with RMSE values between 0.12 and 0.23 mm, well below the 1.0 mm threshold.
Conclusion
High temporal synchronization and spatial agreement were demonstrated among Anzai, NDI, and OTS systems under controlled phantom conditions, supporting respiratory surrogate equivalence. NDI may serve as a complementary surrogate to maintain temporal consistency when conventional optical tracking is degraded in geometrically constrained or non-conventional treatment geometries, including upright particle therapy. Future work will investigate physiologically realistic respiratory patterns and integrate 4DCT phase-binning to develop patient-specific mappings between external respiratory surrogates for consistent respiratory phase definition. The UPLIFT project is funded by the European Union under Grant Agreement No. 101168955.