title: 3D surface imaging for monitoring intrafraction motion in frameless stereotactic body radiotherapy of lung cancer.
abstract: OBJECTIVE
  To investigate the accuracy of surface imaging for monitoring intrafraction motion purposes in frameless stereotactic body radiotherapy (SBRT) of lung cancer by comparison with cone-beam computed tomography (CBCT).
  
  
  METHODS
  Thirty-six patients (18 males, 18 females) were included. During each fraction, three CBCT scans were acquired; CBCT1: before treatment, CBCT2: after correction for tumor misalignment, and CBCT3: after treatment. Intrafraction motion was derived by registering CBCT2 and CBCT3 to the mid-ventilation planning CT scan. Surfaces were captured concurrently with CBCT acquisitions. Retrospectively, for each set of surfaces, an average surface was created: Surface1, Surface2, and Surface3. Subsequently, Surface3 was registered to Surface2 to assess intrafraction motion. For the differences between CBCT- and surface-imaging-derived 3D intrafraction motions, group mean, systematic error, random error and limits of agreement (LOA) were calculated.
  
  
  RESULTS
  Group mean, systematic and random errors were smaller for females than for males: 0.4 vs. 1.3, 1.3 vs. 3.1, and 1.7 vs. 3.3 mm respectively. For female patients deviations between CBCT-tumor- and 3D-surface-imaging-derived intrafraction motions were between -3.3 and 4.3 mm (95% LOA). For male patients these were substantially larger: -5.9-9.5mm.
  
  
  CONCLUSIONS
  Surface imaging is a promising technology for monitoring intrafraction motion purposes in SBRT for female patients.
authors.affiliation: Department of Radiation Oncology, The Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital, Amsterdam, The Netherlands.
authors.forename: Tanja
authors.initials: T
authors.lastname: Alderliesten
authors.forename: Jan-Jakob
authors.initials: JJ
authors.lastname: Sonke
authors.forename: Anja
authors.initials: A
authors.lastname: Betgen
authors.forename: Corine
authors.initials: C
authors.lastname: van Vliet-Vroegindeweij
authors.forename: Peter
authors.initials: P
authors.lastname: Remeijer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D054893:Cone-Beam Computed Tomography; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D009068:Movement; D016634:Radiosurgery / Q000379:methods*