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Effect of Gantry Speed On Accuracy of Extracted Target Motion Trajectories and Image Quality in 4D-CBCT: Phantom Study

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Y Yuasa

Y Yuasa1,2*, T Shiinoki1 , K Fujimoto1,2 , H Hanazawa1 , T Uehara2 , M Koike2 , K Shibuya1 , (1)Yamaguchi University, Ube, Yamaguchi, (2)Yamaguchi University Hospital, Ube, Yamaguchi


WE-RAM3-GePD-J(A)-1 (Wednesday, August 2, 2017) 10:30 AM - 11:00 AM Room: Joint Imaging-Therapy ePoster Lounge - A

Purpose: The purpose of this study was to evaluate the effect of gantry speed (GS) on the tumor motion trajectory, image quality and imaging dose for four-dimensional cone-beam computed tomography (4D-CBCT).

Methods: A Quaser respiratory motion phantom was positioned at the isocentre. A lung-equivalent phantom with the spherical tumor was inserted into the Quaser respiratory motion phantom. The lung-equivalent phantom was driven based on sinusoidal wave patterns (amplitude = 5 mm, respiratory period = 3 s, 6 s). The motion of the lung-equivalent phantom was monitored using a laser displacement gauge (LDG). 4D-CBCT acquisition was performed using an on-board imager mounted on a TrueBeam. The acquisition GS for 4D-CBCT varied from 1 to 6 °/s in steps of 1 °/s. For all GSs, the tumor volume and diameter measured using 4D-CBCT were compared with those measured using reference image. The tumor centroid positions measured using 4D-CBCT were compared with phantom positions measured using the LDG. For the image quality, the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. In addition, weighted CT dose index (CTDIw) was measured using chamber and CTDI phantom.

Results: For the tumor motion trajectories, there was significant difference in tumor volume between GSs of 1 and 6 °/s for the period of 6 s (p<0.05). There was no significant difference in tumor diameter for all GSs. The differences between the tumor centroid positions of 4D-CBCT and phantom positions of the LDG were within 1.5 mm for all GSs. For image quality, The SNRs were 1.3 ± 0.6 and 1.3 ±0.4, the CNRs were 23.5 ± 4.2 and 18.0 ± 4.2 for the respiratory periods of 3 s and 6 s, respectively. The CTDIw ranged from 0.56 to 3.38 cGy.

Conclusion: For clinical implementation, it might be necessary to optimize the acquisition parameter of 4D-CBCT.

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