title: Quantifying the interfractional displacement of the gastroesophageal junction during radiation therapy for esophageal cancer.
abstract: OBJECTIVE
  Accounting for interfractional changes in tumor location improves the accuracy of radiation treatment delivery. The purpose of this study was to quantify the interfractional displacement of the gastroesophageal junction (GEJ) based on standard treatment setup in patients with esophageal cancer undergoing radiation therapy.
  
  
  METHODS
  Free-breathing four-dimensional computed tomography (4D-CT) datasets were acquired weekly from 22 patients during treatment for esophageal adenocarcinoma. Scans were registered to baseline (simulation) 4D-CT scans by using bony landmarks. The distance between the center of the GEJ contour on the simulation scan and the mean location of GEJ centers on subsequent scans was used to assess changes in GEJ location between fractions; displacement was also correlated with clinical and respiratory variables.
  
  
  RESULTS
  The mean absolute random error was 1.69 mm (range, 0.11-4.11 mm) in the lateral direction, 1.87 mm (range, 0.51-4.09 mm) in the anterior-posterior (AP) direction, and 3.09 mm (range, 0.99-6.16 mm) in the superior-inferior (SI) direction. The mean absolute systemic GEJ displacement between fractions was 2.88 mm lateral (≥ 5 mm in 14%), mostly leftward; 2.90 mm (≥ 5 mm in 14%) AP, mostly anterior; and 6.77 mm (≥ 1 cm in 18%) SI, mostly inferior. Variations in tidal volume and diaphragmatic excursion during treatment correlated strongly with systematic SI GEJ displacement (r = 0.964, p < 0.0001; and r = 0.944, p < 0.0001, respectively) and moderately with systematic AP GEJ displacement (r = 0.678, p = 0.0005; r = 0.758, p < 0.0001, respectively). Systematic displacement in the inferior direction resulted in higher-than-intended doses (≥ 60 Gy) to the GEJ, with increased hot-spot to the adjacent stomach and lung base.
  
  
  CONCLUSIONS
  We found large (>1-cm) interfractional displacements in the GEJ in the SI (especially inferior) direction that was not accounted for when skeletal alignment alone was used for patient positioning. Because systematic displacement in the SI direction had dosimetric impact and correlated with tidal volume, better accounting for depth of breathing is needed to reduce interfractional variability.
authors.affiliation: Department of Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Jingya
authors.initials: J
authors.lastname: Wang
authors.forename: Steven H
authors.initials: SH
authors.lastname: Lin
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
authors.forename: Peter
authors.initials: P
authors.lastname: Balter
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Komaki
authors.forename: James D
authors.initials: JD
authors.lastname: Cox
authors.forename: George
authors.initials: G
authors.lastname: Starkschall
mesh_terms: D000230:Adenocarcinoma / Q000000981:diagnostic imaging* / Q000628:therapy; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging*; D059248:Chemoradiotherapy; D019583:Dose Fractionation, Radiation; D004938:Esophageal Neoplasms / Q000000981:diagnostic imaging* / Q000628:therapy; D004943:Esophagogastric Junction / Q000000981:diagnostic imaging*; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008297:Male; D008875:Middle Aged; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D061106:Radiotherapy Setup Errors; D012119:Respiration