title: Prolonged treatment time deteriorates positioning accuracy for stereotactic radiosurgery.
abstract: BACKGROUND
  The accuracy of radiation delivery is increasingly important as radiotherapy technology continues to develop. The goal of this study was to evaluate intrafractional motion during intracranial radiosurgery and the relationship between motion change and treatment time.
  
  
  METHODS
  A total of 50 treatment records with 5988 images, all acquired during treatments with the CyberKnife Radiosurgery System, were retrospectively analyzed in this study. We measured translation and rotation motion including superior-inferior (SI), right-left (RL), anterior-posterior (AP), roll, tilt and yaw. All of the data was obtained during the first 45 minutes of treatment. The records were divided into 3 groups based on 15-min time intervals following the beginning of treatment: group A (0-15 min), group B (16-30 min) and group C (31-45 min). The mean deviations, systematic errors, random errors and margin for planning target volume (PTV) were calculated for each group.
  
  
  RESULTS
  The mean deviations were less than 0.1 mm in all three translation directions in the first 15 minutes. Greater motion occurred with longer treatment times, especially in the SI direction. For the 3D vector, a time-dependent change was observed, from 0.34 mm to 0.77 mm (p=0.01). There was no significant correlation between the treatment time and deviations in the AP, LR and rotation axes. Longer treatment times were associated with increases in systematic error, but not in random error. The estimated PTV margin for groups A, B and C were 0.86 / 1.14 / 1.31 mm, 0.75 / 1.12 / 1.20 mm, and 0.43 / 0.54 / 0.81 mm in the SI, RL, and AP directions, respectively.
  
  
  CONCLUSIONS
  During intracranial radiosurgery, a consistent increase in the positioning deviation over time was observed, especially in the SI direction. If treatment time is greater than 15 minutes, we recommend increasing the PTV margins to ensure treatment precision.
authors.affiliation: Division of Radiation Oncology, Departments of Oncology, National Taiwan University Hospital, Taipei, Taiwan; Department of Radiology, College of Medicine, National Taiwan University, Taipei, Taiwan.
authors.forename: Chun-Wei
authors.initials: CW
authors.lastname: Wang
authors.affiliation: CyberKnife Center, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Yin-Chun
authors.initials: YC
authors.lastname: Lin
authors.affiliation: Division of Neurosurgery, Department of Surgery, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Ham-Min
authors.initials: HM
authors.lastname: Tseng
authors.affiliation: Division of Neurosurgery, Department of Surgery, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Furen
authors.initials: F
authors.lastname: Xiao
authors.affiliation: Division of Neurosurgery, Department of Surgery, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Chang-Mu
authors.initials: CM
authors.lastname: Chen
authors.affiliation: CyberKnife Center, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Wei-Li
authors.initials: WL
authors.lastname: Cheng
authors.affiliation: Division of Radiation Oncology, Departments of Oncology, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Szu-Huai
authors.initials: SH
authors.lastname: Lu
authors.affiliation: Division of Radiation Oncology, Departments of Oncology, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Keng-Hsueh
authors.initials: KH
authors.lastname: Lan
authors.affiliation: Division of Radiation Oncology, Departments of Oncology, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Wan-Yu
authors.initials: WY
authors.lastname: Chen
authors.affiliation: Division of Radiation Oncology, Departments of Oncology, National Taiwan University Hospital, Taipei, Taiwan.
authors.forename: Hsiang-Kuang
authors.initials: HK
authors.lastname: Liang
authors.affiliation: Division of Radiation Oncology, Departments of Oncology, National Taiwan University Hospital, Taipei, Taiwan; Graduate Institute of Oncology, National Taiwan University, Taipei, Taiwan.
authors.forename: Sung-Hsin
authors.initials: SH
authors.lastname: Kuo
mesh_terms: D006801:Humans; D061646:Operative Time; D056888:Patient Positioning; D011857:Radiographic Image Interpretation, Computer-Assisted; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted; D012399:Rotation; D013997:Time Factors