title: Assessment of intrafraction mediastinal and hilar lymph node movement and comparison to lung tumor motion using four-dimensional CT.
abstract: OBJECTIVE
  To quantify the amount of free-breathing motion measured using Four-dimensional (4D) CT scans of mediastinal and hilar lymph nodes and to compare this motion to the primary lung tumor motion.
  
  
  METHODS
  Twenty patients with primary lung cancer, radiographically positive lymph nodes, and prior 4D CT scans were retrospectively analyzed. The 4D CT data sets were divided into four respiratory phases, and the primary tumor and radiographically positive nodes were contoured. Geometric and volumetric analysis was performed to analyze the motion of the primary tumors and the lymph nodes.
  
  
  RESULTS
  The mean lymph node motion was 2.6 mm in the mediolateral direction, 2.5 mm in the anterior-posterior direction, and 5.2 mm in the cranial-caudal direction with a maximum of 14.4 mm. All lymph nodes were found to move inferiorly during inspiration, with 12.5% of nodes moving more than 1 cm. Lymph nodes located below the carina showed significantly more motion than those above the carina (p = 0.01). In comparing the primary tumor motion to the lymph node motion, no correlation was identified.
  
  
  CONCLUSIONS
  Four-dimensional CT scans can be used to measure the motion of the primary lung tumor and pathologic lymph nodes encountered during the respiratory cycle. Both the primary lung tumor and the lymph node must to be examined to assess their individual degree of motion. This study demonstrates the need for individualized plans to assess the heterogeneous motion encountered in both primary lung tumors and among lymph node stations.
authors.affiliation: Department of Radiation Oncology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Donnelly
authors.forename: Parag J
authors.initials: PJ
authors.lastname: Parikh
authors.forename: Wei
authors.initials: W
authors.lastname: Lu
authors.forename: Tianyu
authors.initials: T
authors.lastname: Zhao
authors.forename: Kristen
authors.initials: K
authors.lastname: Lechleiter
authors.forename: Michelle
authors.initials: M
authors.lastname: Nystrom
authors.forename: James P
authors.initials: JP
authors.lastname: Hubenschmidt
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Low
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Bradley
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D008198:Lymph Nodes / Q000000981:diagnostic imaging*; D008482:Mediastinum / Q000000981:diagnostic imaging*; D008875:Middle Aged; D009068:Movement; D011880:Radiotherapy Planning, Computer-Assisted; D012119:Respiration; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*