title: Impact of reduction of flux overlap region on kilovoltage cone-beam computed tomography image quality and patients' exposure dose.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  RESULTS
  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.
  
  
  CONCLUSIONS
  Dose reduction is possible by reducing the overlap region after calibration and by performing computed tomography in the appropriate overlap region.
authors.affiliation: Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Japan; Course of Medical and Dental Sciences, Graduate School of Biomedical & Health Sciences, Hiroshima University, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Kawahara
authors.affiliation: Department of Radiation Oncology, Institute of Biomedical & Health Sciences, Hiroshima University, Japan.
authors.forename: Shuichi
authors.initials: S
authors.lastname: Ozawa
authors.affiliation: Department of Radiation Oncology, Institute of Biomedical & Health Sciences, Hiroshima University, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Murakami
authors.affiliation: Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Japan.
authors.forename: Takeo
authors.initials: T
authors.lastname: Nakashima
authors.affiliation: Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Japan.
authors.forename: Masamichi
authors.initials: M
authors.lastname: Aita
authors.affiliation: Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Japan.
authors.forename: Shintaro
authors.initials: S
authors.lastname: Tsuda
authors.affiliation: Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Ochi
authors.affiliation: Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Japan.
authors.forename: Takuro
authors.initials: T
authors.lastname: Okumura
authors.affiliation: Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Japan.
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Masuda
authors.affiliation: Section of Radiation Therapy, Department of Clinical Support, Hiroshima University Hospital, Japan.
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Ohno
authors.affiliation: Department of Radiation Oncology, Institute of Biomedical & Health Sciences, Hiroshima University, Japan.
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Nagata
keywords: Cone beam CT; Flux overlap region; IGRT