title: Setup variations in radiotherapy of esophageal cancer: evaluation by daily megavoltage computed tomographic localization.
abstract: OBJECTIVE
  To use pretreatment megavoltage computed tomography (MVCT) scans to evaluate setup variations in anterior-posterior (AP), lateral, and superior-inferior (SI) directions and rotational variations, including pitch, roll, and yaw, for esophageal cancer patients treated with helical tomotherapy.
  
  
  METHODS
  Ten patients with locally advanced esophageal cancer treated by combined chemoradiation using helical tomotherapy were selected. After patients were positioned using their skin tattoos/marks, MVCT scans were performed before every treatment and automatically registered to planning kilovoltage CT scans according to bony landmarks. Image registration data were used to adjust patient setups before treatment. A total of 250 MVCT scans were analyzed. Correlations between setup variations and body habitus, including height, weight, relative weight change, body surface area, and patient age, were evaluated.
  
  
  RESULTS
  The standard deviations for systematic setup corrections in AP, lateral, and SI directions and pitch, roll, and yaw rotations were 1.5, 3.7, and 4.8 mm and 0.5 degrees, 1.2 degrees, and 0.8 degrees, respectively. The appropriate averages of random setup variations in AP, lateral, and SI directions and pitch, roll, and yaw rotations were 2.9, 5.2, and 4.4 mm, and 1.0 degrees, 1.2 degrees, and 1.1 degrees, respectively. Setup variations were stable throughout the entire course of radiotherapy in all three translational and three rotational displacements, with little change in magnitude. No significant correlations were found between setup variations and body habitus variables.
  
  
  CONCLUSIONS
  Daily MVCT scans before each treatment can effectively detect setup errors and thereby reduce planning target volume (PTV) margins. This will reduce radiation dose to critical organs and may translate into lower treatment-related toxicities.
authors.affiliation: Division of Radiation Oncology, City of Hope National Medical Center, Duarte, CA 91010-3000, USA.
authors.forename: Yi-Jen
authors.initials: YJ
authors.lastname: Chen
authors.forename: Chunhui
authors.initials: C
authors.lastname: Han
authors.forename: An
authors.initials: A
authors.lastname: Liu
authors.forename: Timothy E
authors.initials: TE
authors.lastname: Schultheiss
authors.forename: Kemp H
authors.initials: KH
authors.lastname: Kernstine
authors.forename: Stephen
authors.initials: S
authors.lastname: Shibata
authors.forename: Nayana L
authors.initials: NL
authors.lastname: Vora
authors.forename: Richard D
authors.initials: RD
authors.lastname: Pezner
authors.forename: Jeffrey Y C
authors.initials: JY
authors.lastname: Wong
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D049628:Body Size; D001830:Body Surface Area; D004938:Esophageal Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal; D012189:Retrospective Studies; D036542:Tomography, Spiral Computed