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. 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).
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging