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Quality Assurance of the Surrogate Signal-Based Dynamic Tumor-Tracking Irradiation with Vero4DRT (MHI-TM2000)

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N Mukumoto

N Mukumoto1*, M Nakamura1, A Sawada1,2, Y Suzuki3, K Takahashi4, Y Miyabe1, S Kaneko4, T Mizowaki1, M Kokubo5, M Hiraoka1, (1) Kyoto University Graduate School of Medicine, Kyoto, JAPAN,(2) Kyoto College of Medical Science, Nantan, JAPAN,(3) Mitsubishi Heavy Industries Ltd., Hiroshima, JAPAN,(4) Kyoto University Hospital, Kyoto, JAPAN,(5) Institute of Biomedical Research and Innovation, Kobe, JAPAN,

WE-G-213CD-9 Wednesday 4:30:00 PM - 6:00:00 PM Room: 213CD

Purpose: To perform the quality assurance for the dynamic tumor-tracking (DTT) irradiation with Vero4DRT (MHI-Tm²000).

Methods: Vero4DRT swings its gimbaled 6-MV C-band x-ray head along the pan and tilt direction to track a moving tumor. Surrogate signal-based DTT system implemented in Vero4DRT was used. Before DTT irradiation, the correlation model (4D-model) between motion of the IR markers on the abdominal wall and the tumor position was created with synchronously monitoring by the IR camera and orthogonal kV x-ray imaging subsystem. During beam delivery, the 4D-model predicted the future tumor position from the displacement of the IR markers in real-time, and then contentiously transferred the corresponding tracking orientation to the gimbaled x-ray head.
Water-equivalent phantoms were set on a 1D motor-driven base with IR markers. A film placed at a depth of 10 cm in the phantom was irradiated under the following conditions: stationary state, and tracking and non-tracking state for sinusoidal patterns. In addition, the geometric accuracy was evaluated using a 3D moving phantom and Polaris Spectra for the previously-acquired patient's respiratory pattern.

Results: Compared to the stationary conditions, reductions in lateral distance between 95% doses of the dose profile were 1.2 mm for tracking and 29.6 mm for non-tracking state for (amplitude [A], period [T]) = (20 mm, 2 s); and 0.2 mm and 29.4 mm for (A, T) = (20 mm, 4 s); and 0.0 mm and 11.2 mm for (A, T) = (10 mm, 2 s), respectively. In the geometric accuracy testing, 95th percentile of the tracking error was 0.5 mm in left-right, 1.0 mm in superior-inferior, and 0.5 mm in anterior-posterior direction.

Conclusions: We demonstrated that Vero4DRT substantially reduced the blurring effects on dose distribution with high tracking accuracy, and confirmed the safety of the DTT irradiation for a clinical application.

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