title: Assessing respiration-induced tumor motion and internal target volume using four-dimensional computed tomography for radiotherapy of lung cancer.
abstract: OBJECTIVE
  To assess three-dimensional tumor motion caused by respiration and internal target volume (ITV) for radiotherapy of lung cancer.
  
  
  METHODS
  Respiration-induced tumor motion was analyzed for 166 tumors from 152 lung cancer patients, 57.2% of whom had Stage III or IV non-small-cell lung cancer. All patients underwent four-dimensional computed tomography (4DCT) during normal breathing before treatment. The expiratory phase of 4DCT images was used as the reference set to delineate gross tumor volume (GTV). Gross tumor volumes on other respiratory phases and resulting ITVs were determined using rigid-body registration of 4DCT images. The association of GTV motion with various clinical and anatomic factors was analyzed statistically.
  
  
  RESULTS
  The proportions of tumors that moved >0.5 cm along the superior-inferior (SI), lateral, and anterior-posterior (AP) axes during normal breathing were 39.2%, 1.8%, and 5.4%, respectively. For 95% of the tumors, the magnitude of motion was less than 1.34 cm, 0.40 cm, and 0.59 cm along the SI, lateral, and AP directions. The principal component of tumor motion was in the SI direction, with only 10.8% of tumors moving >1.0 cm. The tumor motion was found to be associated with diaphragm motion, the SI tumor location in the lung, size of the GTV, and disease T stage.
  
  
  CONCLUSIONS
  Lung tumor motion is primarily driven by diaphragm motion. The motion of locally advanced lung tumors is unlikely to exceed 1.0 cm during quiet normal breathing except for small lesions located in the lower half of the lung.
authors.affiliation: Department of Radiation Physics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA. hliu@mdanderson.org
authors.forename: H Helen
authors.initials: HH
authors.lastname: Liu
authors.forename: Peter
authors.initials: P
authors.lastname: Balter
authors.forename: Teresa
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authors.lastname: Tutt
authors.forename: Bum
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authors.lastname: Choi
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authors.lastname: Zhang
authors.forename: Catherine
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authors.lastname: Wang
authors.forename: Melinda
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authors.forename: Dershan
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authors.lastname: Luo
authors.forename: Tinsu
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authors.forename: Sandeep
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authors.lastname: Hunjan
authors.forename: George
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authors.lastname: Starkschall
authors.forename: Isaac
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authors.lastname: Rosen
authors.forename: Karl
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authors.lastname: Prado
authors.forename: Zhongxing
authors.initials: Z
authors.lastname: Liao
authors.forename: Joe
authors.initials: J
authors.lastname: Chang
authors.forename: Ritsuko
authors.initials: R
authors.lastname: Komaki
authors.forename: James D
authors.initials: JD
authors.lastname: Cox
authors.forename: Radhe
authors.initials: R
authors.lastname: Mohan
authors.forename: Lei
authors.initials: L
authors.lastname: Dong
mesh_terms: D045853:Exhalation; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D009068:Movement; D012119:Respiration; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden