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Volume 21, Number 5, 2016

Impact of reduction of flux overlap region on kilovoltage cone-beam computed tomography image quality and patients’ exposure dose

Daisuke Kawahara, Shuichi Ozawa, Yuji Murakami, Takeo Nakashima, Masamichi Aita, Shintaro Tsuda, Yusuke Ochi, Takuro Okumura, Hirokazu Masuda, Yoshimi Ohno, Yasushi Nagata



In high-precision radiation therapy, kilovoltage cone-beam computed tomography plays an important role in verifying the position of patient and localization of the target. However, the exposure dose is a problem with kilovoltage cone-beam computed tomography. Flux overlap region increases the patient dose around the center when the scan is performed in a full-scan mode. We assessed the influence of flux overlap region in a full-scan mode to understand the relationship between dose and image quality and investigated methods to achieve a dose reduction.


A Catphan phantom was scanned using various flux overlap region patterns in the pelvis on a full-scan mode. We used an intensity-modulated radiation therapy phantom for measuring the central dose. DoseLab was used to perform image analysis and to evaluate the linearity of the computed tomography values, uniformity, high-contrast resolution, and contrast-to-noise ratio.


The Hounsfield unit value varied by ±40 Hounsfield unit of the acceptance value for the X1 field size of 3.5 cm. However, there were no differences in high-contrast resolution and contrast-to-noise ratio among different scan patterns. The absorbed dose decreased by 7% at maximum for the case within the tolerance value.


Dose reduction is possible by reducing the overlap region after calibration and by performing computed tomography in the appropriate overlap region.

Signature: Rep Pract Oncol Radiother, 2016; 21(5) : 460-465

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