title: Log-file analysis of accuracy of beam localization for brain tumor treatment by CyberKnife.
abstract: OBJECTIVE
  The CyberKnife system generates log-files including actual treatment parameters for each procedure. In this study, log-files were analyzed to evaluate the mechanical uncertainty in beam localization over the long term (approximately 1 year), as were patterns of patient movements during brain tumor treatments using CyberKnife.
  
  
  METHODS
  The clinical to planning target volume (CTV-PTV) margin in clinical use was examined based on this analysis. Log-file analysis was performed using data from 140 brain tumor patients (267 treatment plans; 27,166 beams; approximately 66 beams/fraction), who underwent CyberKnife stereotactic radiosurgery and radiation therapy. We calculated a mean error and 2 standard deviations (2σ) for this population. Additionally, we calculated the radius R95%spatially covering 95% of all error vectors.
  
  
  RESULTS
  The mean mechanical uncertainties of CyberKnife brain tumor treatment were found to be 0.07, 0.01, and -0.09 mm in the +inferior/-superior, +left/-right, and +anterior/-posterior directions, respectively. The mean (2σ) of R95%was 1.02 (0.42) mm. A smaller degree of correlation between patient movement and R95%was observed.
  
  
  CONCLUSIONS
  The CyberKnife is robust in tracking accuracy, regardless of patient movement. The effectiveness of log-file analysis was demonstrated regarding quality control for monitoring beam localization in the CyberKnife system. The CTV-PTV margin of 2.0 mm was found to be adequate in brain tumor treatments using the CyberKnife.
authors.affiliation: Department of Radiation Oncology, National Cancer Center Hospital, Tokyo Japan. Electronic address: hiokamot@ncc.go.jp.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Okamoto
authors.affiliation: Department of Radiation Oncology, National Cancer Center Hospital, Tokyo Japan.
authors.forename: Minoru
authors.initials: M
authors.lastname: Hamada
authors.affiliation: Department of Radiation Oncology, National Cancer Center Hospital, Tokyo Japan.
authors.forename: Emi
authors.initials: E
authors.lastname: Sakamoto
authors.affiliation: Department of Radiation Oncology, National Cancer Center Hospital, Tokyo Japan.
authors.forename: Akihisa
authors.initials: A
authors.lastname: Wakita
authors.affiliation: Department of Radiation Oncology, National Cancer Center Hospital, Tokyo Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Nakamura
authors.affiliation: Department of Radiation Oncology, National Cancer Center Hospital, Tokyo Japan.
authors.forename: Toru
authors.initials: T
authors.lastname: Kato
authors.affiliation: Department of Radiation Oncology, National Cancer Center Hospital, Tokyo Japan.
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Abe
authors.affiliation: Department of Radiation Oncology, National Cancer Center Hospital, Tokyo Japan.
authors.forename: Kana
authors.initials: K
authors.lastname: Takahashi
authors.affiliation: Department of Radiation Oncology, National Cancer Center Hospital, Tokyo Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Igaki
authors.affiliation: Department of Radiation Oncology, National Cancer Center Hospital, Tokyo Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Itami
mesh_terms: D001932:Brain Neoplasms / Q000601:surgery*; D006801:Humans; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061089:Radiotherapy, Image-Guided / Q000379:methods*