title: Clinical assessment and characterization of a dual tube kilovoltage X-ray localization system in the radiotherapy treatment room.
abstract: BACKGROUND
  Although flat-panel based X-ray imaging has been well tested in diagnostic radiology, its use as an image-guided-radiotherapy (IGRT) system in a treatment room is new and requires systematic assessment.
  
  
  METHODS
  BrainLab Novalis IGRT system was used for this study. It consists of two floor mounted kV X-ray tubes projecting obliquely into two flat-panel detectors mounted on the ceiling. The system automatically fuses the 2D localization images with 3D simulation CT image to provide positioning guidance. The following characteristics of the system were studied: (1) Coincidence of the isocenters between the IGRT and Linac; (2) Image quality; (3) Exposure; (4) Linearity, uniformity and repeatability.
  
  
  RESULTS
  (1) Localization accuracy and coincidence of the isocenters between the IGRT and Linac was better than 1-mm. (2) The spatial resolution was quantified using the relative modulation-transfer-function with f50=0.7-0.9 lp/mm. The variation of contrast-noise-ratio with technical settings was measured. (3) The maximal exposure of an image was less than 95 mR. An empirical relation between the exposure and the X-ray technical setting was derived. (4) The linearity, uniformity and repeatability of the system generally meet the requirements.
  
  
  CONCLUSIONS
  The system can be safely and reliably used as a target localization device.
authors.affiliation: Radiation Oncology, St. Anne's Hospital, Fall River, Massachusetts.
authors.forename: Sung-Woo
authors.initials: SW
authors.lastname: Lee
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan.
authors.forename: Jian-Yue
authors.initials: JY
authors.lastname: Jin
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan.
authors.forename: Huaiqun
authors.initials: H
authors.lastname: Guan
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan.
authors.forename: Flavious
authors.initials: F
authors.lastname: Martin
authors.affiliation: Department of Radiation Oncology, Henry Ford Health System, Detroit, Michigan.
authors.forename: Jae Ho
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Radiation Oncology, Duke University Medical Center, North Carolina, U.S.A.
authors.forename: Fang-Fang
authors.initials: FF
authors.lastname: Yin
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000295:instrumentation* / Q000379:methods; D011874:Radiometry / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000295:instrumentation* / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation* / Q000379:methods; D014963:X-Ray Intensifying Screens