title: Quantification of motion of different thoracic locations using four-dimensional computed tomography: implications for radiotherapy planning.
abstract: OBJECTIVE
  To assess the respiratory motion of different thoracic nodal locations and its dependence on the presence of enlarged nodes; to assess the respiratory motion of different parenchymal tumor locations; and to determine the appropriate margins to cover the respiratory motion of targets at these locations.
  
  
  METHODS
  We reviewed the four-dimensional computed tomography scans of 20 patients with thoracic tumors treated at our institution. The motion of four central thoracic locations (aortic arch, carina, and bilateral hila), parenchymal tumor locations (upper vs. lower, and anterior vs. middle vs. posterior thorax), and bilateral diaphragmatic domes was measured.
  
  
  RESULTS
  For the central thoracic locations, the largest motion was in the superoinferior (SI) dimension (>5 mm for bilateral hila and carina, but <4 mm for aortic arch). No significant difference was found in the motion of these locations in the absence or presence of enlarged nodes. For parenchymal tumors, upper tumors exhibited smaller SI motion than did lower tumors (3.7 vs. 10.4 mm, p = 0.029). Similarly, anterior tumors exhibited smaller motion than did posterior tumors in both the SI (4.0 vs. 8.0 mm, p = 0.013) and lateral (2.8 vs. 4.6 mm, p = 0.045) directions. The margins that would be needed to encompass the respiratory motion of each of the evaluated locations in 95% of patients were tabulated and range from 3.4 to 37.2 mm, depending on the location and direction.
  
  
  CONCLUSIONS
  The results of our study have provided data for appropriate site-specific internal target volume expansion that could be useful in the absence of four-dimensional computed tomography-based treatment planning. However, generalizing the results from a small patient population requires discretion.
authors.affiliation: Department of Radiation Oncology, Stanford University, Stanford, CA 94305, USA.
authors.forename: Peter G
authors.initials: PG
authors.lastname: Maxim
authors.forename: Billy W
authors.initials: BW
authors.lastname: Loo
authors.forename: Haider
authors.initials: H
authors.lastname: Shirazi
authors.forename: Brian
authors.initials: B
authors.lastname: Thorndyke
authors.forename: Gary
authors.initials: G
authors.lastname: Luxton
authors.forename: Quynh-Thu
authors.initials: QT
authors.lastname: Le
mesh_terms: D000368:Aged; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D008198:Lymph Nodes / Q000000981:diagnostic imaging*; D008207:Lymphatic Metastasis / Q000000981:diagnostic imaging; D008297:Male; D008875:Middle Aged; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D013909:Thorax; D014057:Tomography, X-Ray Computed / Q000379:methods*