Performance Evaluation of Visual Guidance Patient-Controlled Respiratory Gating System for Respiratory-Gated Magnetic-Resonance Image-Guided Radiation Therapy

Abstract

To evaluate the performance of visual guidance patient-controlled (VG-PC) respiratory gating system for respiratory-gated magnetic-resonance image-guided radiation therapy (MR-IGRT) and to investigate the relationship between patient specific factors and the performance of the system.The VG-PC respiratory gating system consists of a beam projector in the treatment room to project the near-real-time cine planar MR images inside the bore of the system in order for patients to monitor the images during treatment. With the visual information, patients voluntarily control their respiration to put the target volume into the gating boundary (gating window). A total of 15 patients with lung or liver tumors who were scheduled for stereotactic ablative radiotherapy (SABR) were selected for the study. A comprehensive instruction about the VG-PC gating system was given to patients before the first treatment. Some of the fractions were treated with the respiratory-gated MR-IGRT combined with the VG-PC gating system, while the remainder of the treatment was performed without the VG-PC gating system (free-breathing). For each fraction the total treatment time, beam-off time owing to the respiratory gating, and number of beam-off events during whole treatment session were analyzed.The average beam-off times due to respiratory gating with and without the VG-PC gating system were 806.0 ± 531.46 s and 1163.7 ± 773.9 s respectively (P < 0.05). Consequently, the average total treatment time was reduced from 2033.5 ± 928.0 s to 1674.7 ± 727.7 s by using the VG-PC gating system (P < 0.05). The average number of beam-off events during whole treatment session was reduced from 395 ± 213 times to 196 ± 127 times by using the VG-PC gating system (P < 0.001). The percent decrease in the average beam-off times due to respiratory gating, the average total treatment time, and the average number of beam-off events for patients with lung cancer are 22.5%, 37.6%, and 51.2% respectively and 3.5%, 6.9% and 47.2% respectively for patients with liver cancer.The VG-PC gating system could improve treatment efficiency when performing respiratory gated MR-IGRT for patients with lung or liver cancer. However, there were no evidences to suggest that other factors including patient's sex, age, and the exact location of the tumor have effect on the performance of the VG-PC gating system.H. Choun: None. H. An: None. H.Jin: None. J. Kim: None. C. Choi: None. J. Park: None.