title: An analysis of anatomic landmark mobility and setup deviations in radiotherapy for lung cancer.
abstract: OBJECTIVE
  To identify thoracic structures that exhibit little internal motion during irradiation and to determine setup variations in patients with lung cancer.
  
  
  METHODS
  Intrafractional images were generated with an electronic portal-imaging device from the AP fields of 10 patients, during several fractions. To determine the intrafractional mobility of thoracic structures, visible structures were contoured in every image and matched with a reference image by means of a cross-correlation algorithm. Setup variations were determined by comparing portal images with the digitized simulator films using the stable structures as landmarks.
  
  
  RESULTS
  Mobility was limited in the lateral direction for the trachea, thoracic wall, paraspinal line, and aortic notch, and in the craniocaudal direction for the clavicle, aortic notch, and thoracic.wall. Analysis of patient setup revealed random deviations of 2.0 mm (1 SD) in the lateral direction and 2.8 mm in the craniocaudal direction, while the systematic deviations were 2.5 and 2.0 mm (1 SD) respectively.
  
  
  CONCLUSIONS
  We have identified thoracic structures that exhibit little internal motion in the frontal plane, and recommend that these structures be used for verifying patient setup during radiotherapy. The daily variation in the setup of lung cancer patients at our center appears to be acceptable.
authors: Department of Radiation Oncology, University Hospital Rotterdam-Daniel den Hoed Cancer Center/University Hospital Rotterdam, The Netherlands.
authors: M J
authors: MJ
authors: Samson
authors: J R
authors: JR
authors: van Sörnsen de Koste
authors: H C
authors: HC
authors: de Boer
authors: H
authors: H
authors: Tankink
authors: M
authors: M
authors: Verstraate
authors: M
authors: M
authors: Essers
authors: A G
authors: AG
authors: Visser
authors: S
authors: S
authors: Senan
mesh_terms: D006801:Humans; D008175:Lung Neoplasms / Q000532:radiotherapy*; D009038:Motion; D015588:Observer Variation; D013902:Radiography, Thoracic; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal; D013909:Thorax / Q000033:anatomy & histology*