title: Target localization errors from fiducial markers implanted around a lung tumor for dynamic tumor tracking.
abstract: OBJECTIVE
  To assess target localization errors (TLEs) from implanted fiducial markers by three different centers of gravity (CG) and three different multiple regression analysis (MRA) approaches.
  
  
  METHODS
  The three-dimensional (3D) positions of the markers were detected on the fluoroscopic images of 15 lung cancer patients, and the marker closest to the tumor was then assumed to be the target (Pt). The estimated target position (Pe) was calculated from three markers adjacent to the target (Pi, 1 ≤ i ≤ 3) using the equation Pe = aP1 + bP2 + cP3 + d. Pe was then calculated using three different CGs and three different MRAs. The TLE was calculated as the root-mean-square error of the difference between Pt and Pe calculated for each fraction. First, we compared the TLE of the first fraction to assess the intrafraction TLE of the six approaches tested. Second, interfraction TLEs were calculated to evaluate the robustness of the coefficients obtained in the first fraction. The interfraction TLE was defined as the difference between the TLE of a later and the first fraction.
  
  
  RESULTS
  The mean plus two times the standard deviation of the intrafraction TLE was up to 4.3 mm in the CG approaches, while the MRA approaches provided TLEs within 1.5 mm. The mean plus two times the standard deviation of the interfraction TLE did not exceed 1.7 mm in any direction using either approach.
  
  
  CONCLUSIONS
  The MRA approach was superior to the CG approach in terms of estimating the target position based on the implanted fiducial markers.
authors.affiliation: Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Japan. Electronic address: m_nkmr@kuhp.kyoto-u.ac.jp.
authors.forename: Mitsuhiro
authors.initials: M
authors.lastname: Nakamura
authors.affiliation: Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Japan; Engineering Division Course, Graduate School of Engineering, Kyoto University, Japan.
authors.forename: Masanori
authors.initials: M
authors.lastname: Takamiya
authors.affiliation: Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Mami
authors.initials: M
authors.lastname: Akimoto
authors.affiliation: Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Nami
authors.initials: N
authors.lastname: Ueki
authors.affiliation: Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Yamada
authors.affiliation: Division of Radiation Oncology, Institute of Biomedical Research and Innovation, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Tanabe
authors.affiliation: Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Nobutaka
authors.initials: N
authors.lastname: Mukumoto
authors.affiliation: Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Yokota
authors.affiliation: Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Yukinori
authors.initials: Y
authors.lastname: Matsuo
authors.affiliation: Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Mizowaki
authors.affiliation: Division of Radiation Oncology, Institute of Biomedical Research and Innovation, Japan; Department of Radiation Oncology, Kobe City Medical Center General Hospital, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Kokubo
authors.affiliation: Department of Radiation Oncology and Image-Applied Therapy, Graduate School of Medicine, Kyoto University, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Hiraoka
mesh_terms: D004548:Elasticity; D057918:Fiducial Markers; D005471:Fluoroscopy / Q000592:standards*; D006112:Gravitation; D006801:Humans; D021621:Imaging, Three-Dimensional; D008175:Lung Neoplasms / Q000000981:diagnostic imaging*; D019300:Medical Errors; D012044:Regression Analysis
keywords: Dynamic tumor tracking; Implanted fiducial markers; Multiple regression analysis; Target localization error