Evaluation of the linearity characteristic of the cone-beam CT fixed on the Varian 23EX linear accelerator

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Author:
ZHANG Jun(Department of Radiation Oncology, Zhongnan Hospital of Wuhan University,Wuhan 430072, China)
XU Li-ming()
LIU Hui(Department of Radiation Oncology, Zhongnan Hospital of Wuhan University,Wuhan 430072, China)
XIE Cong-hua(Department of Radiation Oncology, Zhongnan Hospital of Wuhan University,Wuhan 430072, China)
ZHONG Ya-hua(Department of Radiation Oncology, Zhongnan Hospital of Wuhan University,Wuhan 430072, China)
ZHOU Fu-xiang(Department of Radiation Oncology, Zhongnan Hospital of Wuhan University,Wuhan 430072, China)
ZHANG Gong(Department of Radiation Oncology, Zhongnan Hospital of Wuhan University,Wuhan 430072, China)
DENG Di(Department of Radiation Oncology, Zhongnan Hospital of Wuhan University,Wuhan 430072, China)
Journal Title:
Chinese Journal of Radiation Oncology
Issue:
Volume 21, Issue 05, 2012
DOI:
10.3760/cma.j.issn.1004-4221.2012.05.020
Key Word:
Tomography, X-ray computed, cone-beam;Linear fitting;Catphan504 phantom

Abstract: Objective To investigate the CT number linearity of the cone-beam CT (CBCT) images at the different spatial locations in the scanning area.Methods The CatphanS04 phantom at the different locations are scanned repeatcdly using the CBCT on the Varian 23EX linear accelerator.The phantom is located the isocenter point,eccentric 3 cm,eccentric 6 cm,and different points on the z-axis successively on the accelerator.The scanned mode is the standard head mode.The reconstructive thickness is 2.5 cm.The different densities inserts of CTP404 module on the different locations are measured via Eclips treatment planning system (TPS) and computed by Matlab 7.0 and the CT linear fitting are then processed.In order to understand better the linear distribution along with the value of CT in the spatial distribution the results are compared with the fan-beam CT.Results Phantom studies show that:CBCT has good linearity performance not only under the standard header (body) of the scanning conditions,but also on such locations including the cross-sectional,the sagittal,the coronal plane and the eccentric position ( R2 > 0.953 ).Bowtie filtration device does not change the CT finearity but changes the value of CT.Conclusions The linearity of X-ray CBCT on the Varian linear accelerator is favorable.CBCT will be used in the TPS dose calculation via further correction of the CT value.

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