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Comparative study of inertial measurement unit and optical tracking systems for respiratory motion management in
Hyeongmin Jin1, Manjin Ha2, Jin Jegal3
1Project Group of the Gijang Heavy Ion Medical Accelerator, Seoul National University Hospital, Seoul 03080, the Republic of Korea; Department of Radiation Oncology, Seoul National University Hospital, Seoul 03080, the Republic of Korea; Biomedical Research Institute, Seoul National University Hospital, Seoul 03080, the Republic of Korea; Department of Radiation Oncology, Seoul National University College of Medicine, Seoul 03080, the Republic of Korea.
Purpose:
To evaluate the feasibility and accuracy of inertial measurement unit (IMU) for respiratory motion tracking and four-dimensional cone-beam computed tomography (4D CBCT) reconstruction in radiotherapy, particularly in scenarios involving limited line-of-sight such as abdominal compression.
Methods:
Respiratory signals were simultaneously acquired using a commercial optical tracking system (Real-time Position Management, RPM) and wireless IMU sensor in twenty healthy volunteers and a dynamic thorax phantom. The phantom was programmed with various motion patterns and amplitudes, and abdominal compression was applied in selected scenarios to simulate clinical obstruction. Signal synchronization and processing were performed using principal component analysis and analyzed by comparing respiratory rate, peak/valley timing, and phase agreement between IMU and RPM signals. The signals were then used for phase-sorted 4D CBCT reconstruction, and images were quantitatively evaluated.
Results:
IMU-derived respiratory signals demonstrated agreement with RPM data across all motion patterns, with average respiratory rate differences below 0.1 bpm and absolute phase discrepancies under 0.1 %. Peak and valley time differences remained below 0.1 s at standard amplitudes (±10 mm), increasing moderately under smaller motion ranges (up to 0.15 s). In 4D CBCT reconstruction, image quality parameters showed no significant differences between IMU and RPM signals indicating comparable geometric fidelity.
Conclusion:
IMU sensors provide a reliable, line-of-sight-independent method for respiratory motion tracking and 4D CBCT reconstruction in radiotherapy. Their robust performance under conditions that hinder optical tracking suggests clinical applicability involving abdominal compression or complex immobilization setups.
