SU-E-J-166: Development of Real-Time Motion Verification System for Respiratory-Gated Radiotherapy

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.

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.

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.

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. This work was supported in part by the SNU Brain Fusion Program Research Grant No. 400-20100049 (2010-2011) and the National Research Foundation of Korea (NRF) grant (800-20110212) funded by the Korea government (MEST).