title: Image-guided radiotherapy via daily online cone-beam CT substantially reduces margin requirements for stereotactic lung radiotherapy.
abstract: OBJECTIVE
  To determine treatment accuracy and margins for stereotactic lung radiotherapy with and without cone-beam CT (CBCT) image guidance.
  
  
  METHODS
  Acquired for the study were 308 CBCT of 24 patients with solitary peripheral lung tumors treated with stereotactic radiotherapy. Patients were immobilized in a stereotactic body frame (SBF) or alpha-cradle and treated with image guidance using daily CBCT. Four (T1) or five (T2/metastatic) 12-Gy fractions were prescribed to the planning target volume (PTV) edge. The PTV margin was >or=5 mm depending on a pretreatment estimate of tumor excursion. Initial daily setup was according to SBF coordinates or tattoos for alpha-cradle cases. A CBCT was performed and registered to the planning CT using soft tissue registration of the target. The initial setup error/precorrection position, was recorded for the superior-inferior, anterior-posterior, and medial-lateral directions. The couch was adjusted to correct the tumor positional error. A second CBCT verified tumor position after correction. Patients were treated in the corrected position after the residual errors were <or=2 mm. A final CBCT after treatment assessed intrafraction tumor displacement.
  
  
  RESULTS
  The precorrection systematic (Sigma) and random errors (sigma) for the population ranged from 2-3 mm for SBF and 2-6 mm for alpha-cradle patients; postcorrection errors ranged from 0.4-1.0 mm. Calculated population margins were 9 to 13 mm (SBF) and 10-14 mm (cradle) precorrection, 1-2 mm (SBF), and 2-3 mm (cradle) postcorrection, and 2-4 mm (SBF) and 2-5 mm (cradle) posttreatment.
  
  
  CONCLUSIONS
  Setup for stereotactic lung radiotherapy using a SBF or alpha-cradle alone is suboptimal. CBCT image guidance significantly improves target positioning and substantially reduces required target margins and normal tissue irradiation.
authors.affiliation: Department of Radiation Oncology, William Beaumont Hospital, Royal Oak, MI 48072, USA. igrills@beaumont.edu
authors.forename: Inga S
authors.initials: IS
authors.lastname: Grills
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Hugo
authors.forename: Larry L
authors.initials: LL
authors.lastname: Kestin
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Galerani
authors.forename: K Kenneth
authors.initials: KK
authors.lastname: Chao
authors.forename: Jennifer
authors.initials: J
authors.lastname: Wloch
authors.forename: Di
authors.initials: D
authors.lastname: Yan
mesh_terms: D000465:Algorithms; D002138:Calibration; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000532:radiotherapy; D054893:Cone-Beam Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy; D009068:Movement; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D013238:Stereotaxic Techniques