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Development of Real-Time Motion Verification System for Respiratory-Gated Radiotherapy

Y Park

Y Park1*, H Kim2, S Park2, H Kim3, K Lee2, I Kim2, S Ye2, (1) Seoul National University Hospital, Seoul,Korea (2) Seoul National University, Seoul, Korea (3) SoonChunHyang University Hospital, Seoul, Korea

SU-E-J-166 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose: To develop an on-line quality assurance tool for RPM (real-time position management system, Varian Medical Systems, Palo Alto, CA) phase-based gated radiotherapy.

Methods: A real-time motion verification system (RMVS) was developed to verify the positional reproducibility of patient breathing between CT simulation and treatment. Phase-resolved anterior body midlines were extracted from the 4D-CT simulation data to constitute 4D reference lines. During the treatment, multiple infrared reflective markers attached on patient's body midline were tracked by a custom stereo camera system. The RPM-generated phase value was delivered to RMVS via in-house network communication software. The real-time positions of tracked markers were simultaneously compared with the 4D reference line dynamically selected according to the phase value. The technical feasibility of the system was evaluated by simulating a motion phantom under several scenarios such as ideal case (with identical motion parameters between simulation and treatment; cycle = 3.1 s, baseline = 0.0 mm, amplitude = 31.0 mm), cycle change, baseline shift, and amplitude change.

Results: The developed system (i.e., RMVS) was fully compatible with RPM. In the phantom experiments, RMVS detected 5.2 ± 1.3, 4.7 ± 1.2, and 9.8 ± 1.2 mm mean absolute errors (MAE) for -5.0, 5.0, and 10.0 mm baseline shifts, respectively. However, revealing about 1.0 mm MAE for both ideal and cycle change scenarios, RMVS turned out to have a systematic error. With 22.0, 26.0, 35.0, and 41.5 mm amplitudes, RMVS detected 2.3 ± 1.3, 1.5 ± 1.1, 2.3 ± 1.4, and 4.9 ± 2.5 mm MAE, respectively.

Conclusions: The developed system demonstrated a competence for phase-matching error detection between real-time patient's motion and 4D-CT-based reference. Thus, it could be used as an on-line quality assurance tool for RPM phase-based radiotherapy.

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