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Application of a Feature-Based Tracking Algorithm to KV X-Ray Fluoroscopic Images Toward Marker-Less Real-Time Tumor Tracking

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M Nakamura

M Nakamura1*, M Nakao2 , Y Matsuo1 , N Mukumoto1 , Y Iizuka1 , K Yokota1 , T Mizowaki1 , M Hiraoka1 , (1) Kyoto University, Graduate School of Medicine, Kyoto, (2) Kyoto University, Graduate School of Informatics, Kyoto


SU-G-BRA-5 (Sunday, July 31, 2016) 4:00 PM - 6:00 PM Room: Ballroom A

Purpose: To detect target position on kV X-ray fluoroscopic images using a feature-based tracking algorithm, Accelerated-KAZE (AKAZE), for markerless real-time tumor tracking (RTTT).

Methods: Twelve lung cancer patients treated with RTTT on the Vero4DRT (Mitsubishi Heavy Industries, Japan, and Brainlab AG, Feldkirchen, Germany) were enrolled in this study. Respiratory tumor movement was greater than 10 mm. Three to five fiducial markers were implanted around the lung tumor transbronchially for each patient. Before beam delivery, external infrared (IR) markers and the fiducial markers were monitored for 20 to 40 s with the IR camera every 16.7 ms and with an orthogonal kV x-ray imaging subsystem every 80 or 160 ms, respectively. Target positions derived from the fiducial markers were determined on the orthogonal kV x-ray images, which were used as the ground truth in this study. Meanwhile, tracking positions were identified by AKAZE. Among a lot of feature points, AKAZE found high-quality feature points through sequential cross-check and distance-check between two consecutive images. Then, these 2D positional data were converted to the 3D positional data by a transformation matrix with a predefined calibration parameter. Root mean square error (RMSE) was calculated to evaluate the difference between 3D tracking and target positions. A total of 393 frames was analyzed. The experiment was conducted on a personal computer with 16 GB RAM, Intel Core i7-2600, 3.4 GHz processor.

Results: Reproducibility of the target position during the same respiratory phase was 0.6 +/- 0.6 mm (range, 0.1-3.3 mm). Mean +/- SD of the RMSEs was 0.3 +/- 0.2 mm (range, 0.0-1.0 mm). Median computation time per frame was 179 msec (range, 154-247 msec).

Conclusion: AKAZE successfully and quickly detected the target position on kV X-ray fluoroscopic images. Initial results indicate that the differences between 3D tracking and target position would be clinically acceptable.

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