Purpose: To demonstrate the efficacy of using mm-wave technology to measure patient surface motion during radiotherapy with sub-millimeter accuracy and extract breathing and cardiac waveforms from chest displacement data.
Methods: A millimeter-wave device was mounted within the bore of a Halcyonâ„¢ System and directed at a volunteer subject. Reflected waves were received at the device with radar subsystem parameters of 512 samples/chirp, 128 chirps/frame, and 10000 frames for a total of 512x128x1000= 65536000 samples. For chest displacement measurements, the subjectâ€™s chest was localized to a coarse range bin through the use of a Fast Fourier Transform on the received data. Small-scale displacement within that range bin was calculated through phase extraction and demodulation of the beat signal. The displacement data was sent through two separate bandpass filters with passbands of 0.1-0.6 Hz and 0.8-4.0 Hz to obtain the subjectâ€™s breathing and cardiac waveforms, respectively.
Results: The system was able to feasibly measure motion and small-scale chest displacements of the subject. Displacement data was used to successfully generate breathing and cardiac waveforms.
Conclusion: Millimeter-wave technology has the potential to monitor patient surface displacements with sub-mm accuracy through masks and clothing. In a clinical setting, this technology has a potential to provide real-time guidance with patientsâ€™ motion, breathing, and cardiac waveforms.