title: Quantification of mediastinal and hilar lymph node movement using four-dimensional computed tomography scan: implications for radiation treatment planning.
abstract: OBJECTIVE
  To quantitatively describe mediastinal and hilar lymph node movement in patients with lymph node-positive lung cancer.
  
  
  METHODS
  Twenty-four patients with lung cancer who underwent four-dimensional computed tomography scanning at Massachusetts General Hospital were included in the study. The maximum extent of superior motion of the superior border was measured, as well as the maximum inferior movement of the inferior border. The average of these two values is defined as the peak-to-peak movement. This process was repeated for mediolateral (ML) and anterior-posterior (AP) movement. Linear regression was used to determine lymph node characteristics associated with peak-to-peak movement. Various uniform expansions were investigated to determine the expansion margins necessary to ensure complete internal target volume (ITV) coverage.
  
  
  RESULTS
  The mean peak-to-peak displacements of paratracheal lymph nodes were 4 mm (craniocaudal [CC]), 2 mm (ML), and 2 mm (AP). For subcarinal lymph nodes, the mean peak-to-peak movements were 6 mm (CC), 4 mm (ML), and 2 mm (AP). The mean peak-to-peak displacements of hilar lymph nodes were 7 mm (CC), 1 mm (ML), and 4 mm (AP). On multivariate analysis, lymph node station and lymph node size were significantly related to peak-to-peak movement. Expansions of 8 mm for paratracheal nodes and 13 mm for subcarinal and hilar nodes would have been necessary to cover the ITV of 95% of these nodal masses.
  
  
  CONCLUSIONS
  Subcarinal and hilar lymph nodes may move substantially throughout the respiratory cycle. In the absence of patient-specific information on nodal motion, expansions of at least 8 mm, 13 mm, and 13 mm should be considered to cover the ITV of paratracheal, subcarinal, and hilar lymph nodes, respectively.
authors.affiliation: Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
authors.forename: David J
authors.initials: DJ
authors.lastname: Sher
authors.forename: John A
authors.initials: JA
authors.lastname: Wolfgang
authors.forename: Andrzej
authors.initials: A
authors.lastname: Niemierko
authors.forename: Noah C
authors.initials: NC
authors.lastname: Choi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; 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; D008482:Mediastinum / Q000000981:diagnostic imaging; D008875:Middle Aged; D009068:Movement; D012119:Respiration; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*