title: Evaluation of respiratory-induced target motion for esophageal tumors at the gastroesophageal junction.
abstract: OBJECTIVE
  To quantify the internal motion margin requirements for radiotherapy of tumors near the gastroesophageal junction (GEJ).
  
  
  METHODS
  Four-dimensional computed tomography (4DCT) scans were obtained for 25 patients with primary tumors located near the GEJ. The gross tumor volume (GTV) was manually contoured on the exhale-phase image from the 4DCT image set. A deformable image registration method was used to automatically propagate the contours to other phases of the 4DCT images. To quantify target motion, we measured the displacement of the GTV centroid and the variations in the target boundary and volume. Internal margins were calculated in the lateral (RL), anterior-posterior (AP), and superior-inferior (SI) directions.
  
  
  RESULTS
  The mean+/-standard deviation peak-to-peak GTV centroid motion was 0.39+/-0.27cm (range, 0.04-1.09cm) in the RL, 0.38+/-0.23cm (range, 0.10-0.94cm) in the AP, and 0.87+/-0.47cm (range, 0.43-2.63cm) in the SI directions, respectively. On average, the internal target volume was 72% (range, 9-172%) larger than the GTV defined on a single-phase CT image. Variations in tumor boundaries due to tissue motion and deformation suggested asymmetric margins: 1.0cm left [toward the stomach], 0.8cm right, 1.1cm anterior, 0.6cm posterior, 1.0cm superior (toward the distal esophagus), and 1.6cm inferior (toward the stomach).
  
  
  CONCLUSIONS
  Because tumors near the GEJ are subject to a marked but asymmetric amount of respiratory-induced intrafractional tumor motion, the use of asymmetric internal margins may be beneficial.
authors: Department of Radiation Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, USA.
authors: Kuai-le
authors: KL
authors: Zhao
authors: Zhongxing
authors: Z
authors: Liao
authors: M Kara
authors: MK
authors: Bucci
authors: Ritsuko
authors: R
authors: Komaki
authors: James D
authors: JD
authors: Cox
authors: Zhiqian H
authors: ZH
authors: Yu
authors: Lifei
authors: L
authors: Zhang
authors: Radhe
authors: R
authors: Mohan
authors: Lei
authors: L
authors: Dong
mesh_terms: D000368:Aged; D004938:Esophageal Neoplasms / Q000000981:diagnostic imaging / Q000503:physiopathology* / Q000532:radiotherapy*; D004943:Esophagogastric Junction; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009038:Motion; D012119:Respiration; D014057:Tomography, X-Ray Computed / Q000379:methods; D047368:Tumor Burden