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Time-Ordered Four Dimensional Cone-Beam CT

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M Nakano

M Nakano*, S Kida, Y Masutani, T Shiraki, K Shiraishi, K Yamamoto, K Nakagawa, A Haga, University of Tokyo Hospital, Bunkyo-ku, Tokyo

SU-E-J-122 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:
Four-dimensional (4D) cone-beam CT (CBCT) techniques have been started to use in clinical sites as a tool of image-guided radiotherapy (IGRT), especially in the treatment of lung tumors. However, those techniques suppose periodic respiratory motion, and there are little approaches to visualize organs which present non-periodic time-ordered motion using CBCT imaging techniques. The present study proposes a method to visualize time-ordered motion including peristaltic motion of gastrointestinal organs and adjacent area.

Methods:
Projection data sets of clinical patients and digital phantom were reconstructed in this study. Patients' data sets were acquired using the X-ray Volume Imaging system (XVI, version 4.2) on Synergy linear accelerator system (Elekta, UK) as pre-treatment CBCT imaging to setup prostate radiotherapy patients with 11.5 cm offset-located flat panel detector (FPD) unit. An elliptic-cylindrical digital phantom which contains a moving air sphere of 3 cm diameter was also reconstructed. These projection data sets were reconstructed using our in-house reconstruction software based on Feldkamp, Davis and Kress (FDK) algorithm. In this study, 180 degrees or less angular ranges of projection data were used to reconstruct CBCT image set of each time phase, and the range moved as time progressed.

Results:
Reconstructed sagittal images of clinical patients visualized that flatus and stool inside rectum moved with the progress of time. Reconstructed sagittal images of digital phantom with several angular ranges of projection showed that the longitudinal length is getting shorter with shorter range of projection, though a shape of a sphere is getting blurred in vertical direction.

Conclusion:
The presented method of time-ordered 4D CBCT reconstruction visualized deformation of intestine and rectum, and motion of flatus and stool, though the method has a trade-off between temporal resolution improvement and image quality degradation.

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