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Proceedings Paper

Measurement-based scatter correction for cone-beam CT in radiation therapy
Author(s): Lei Zhu; Lei Xing
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Paper Abstract

Cone-beam CT (CBCT) is being increasingly used in modern radiation therapy. However, as compared to conventional CT, the degraded image quality of CBCT hampers its applications in radiation therapy. Due to the large volume of x-ray illumination, scatter is considered as one of the fundamental limitations of CBCT image quality. Many scatter correction algorithms have been proposed in the literature, while drawbacks still exist. In this work, we propose a correction algorithm which is particularly useful in radiation therapy. Since the same patient is scanned repetitively during one radiation treatment course, we measure the scatter distribution in one scan, and use the measured scatter distribution to estimate and correct scatter in the following scans. A partially blocked CBCT is used in the scatter measurement scan. The x-ray beam blocker has a strip pattern, such that the whole-field scatter distribution can be estimated from the detected signals in the shadow region and the patient rigid transformation can be determined from the reconstructed image using the illuminated detector projection data. From the derived patient transformation, the measured scatter is then modified accordingly and used for scatter correction in the following regular CBCT scans. The proposed method has been evaluated using Monte Carlo simulations and physical experiments on an anthropomorphic chest phantom. The results show a significant suppression of scatter artifacts using the proposed method. Using the reconstruction in a narrow collimator geometry as a reference, the comparison also shows that the proposed method reduces reconstruction error from 13.2% to 3.8%. The proposed method is attractive in applications where a high CBCT image quality is critical, for example, dose calculation in adaptive radiation therapy.

Paper Details

Date Published: 13 March 2009
PDF: 8 pages
Proc. SPIE 7258, Medical Imaging 2009: Physics of Medical Imaging, 72583C (13 March 2009); doi: 10.1117/12.813870
Show Author Affiliations
Lei Zhu, Stanford Univ. (United States)
Lei Xing, Stanford Univ. (United States)

Published in SPIE Proceedings Vol. 7258:
Medical Imaging 2009: Physics of Medical Imaging
Ehsan Samei; Jiang Hsieh, Editor(s)

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