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Development of a Video Guided Real-Time Patient Motion Monitoring System for Helical Tomotherpay

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C Hong

S Ju1, C Hong1*, D Yim1, M Kim1,2, J Kim1, Y Han1, J Shin1, E Shin1, S Ahn1, D Choi1, (1) Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea, (2) Department of Electronics Engineering, Myongji University, Gyeonggi-do, Korea

SU-E-J-172 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose:
We developed a video image-guided real-time patient motion monitoring system for helical Tomotherapy (VGRPM-Tomo), and its clinical utility was evaluated using a motion phantom.

Methods:
The VGRPM-Tomo consisted of three components: an image acquisition device consisting of two PC-cams, a main control computer with a radiation signal controller and warning system, and patient motion analysis software, which was developed in house. The system was designed for synchronization with a beam on/off trigger signal to limit operation during treatment time only and to enable system automation. In order to detect the patient motion while the couch is moving into the gantry, a reference image, which continuously updated its background by exponential weighting filter (EWF), is compared with subsequent live images using the real-time frame difference-based analysis software. When the error range exceeds the set criteria (d_movement) due to patient movement, a warning message is generated in the form of light and sound. The described procedure repeats automatically for each patient. A motion phantom, which operates by moving a distance of 0.1, 0.2, 0.5, and 1.0 cm for 1 and 2 sec, respectively, was used to evaluate the system performance at maximum couch speed (0.196 cm/sec) in a Helical Tomotherapy (HD, Hi-art, Tomotherapy, USA). We measured the optimal EWF factor (a) and d_movement, which is the minimum distance that can be detected with this system, and the response time of the whole system.

Results:
The optimal a for clinical use ranged from 0.85 to 0.9. The system was able to detect phantom motion as small as 0.2 cm with tight d_movement, 0.1% total number of pixels in the reference image. The measured response time of the whole system was 0.1 sec.

Conclusions:
The VGRPM-tomo can contribute to reduction of treatment error caused by the motion of patients and increase the accuracy of treatment dose delivery in HD.

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