Comparative study of inertial measurement unit and optical tracking systems for respiratory motion management in radiotherapy.

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.