title: 4DCT and CBCT based PTV margin in Stereotactic Body Radiotherapy(SBRT) of non-small cell lung tumor adhered to chest wall or diaphragm.
abstract: BACKGROUND
  Large tumor motion often leads to larger treatment volumes, especially the lung tumor located in lower lobe and adhered to chest wall or diaphragm. The purpose of this work is to investigate the impacts of planning target volume (PTV) margin on Stereotactic Body Radiotherapy (SBRT) in non-small cell lung cancer (NSCLC).
  
  
  METHODS
  Subjects include 20 patients with the lung tumor located in lower lobe and adhered to chest wall or diaphragm who underwent SBRT. Four-dimensional computed tomography (4DCT) were acquired at simulation to evaluate the tumor intra-fractional centroid and boundary changes, and Cone-beam Computer Tomography (CBCT) were acquired during each treatment to evaluate the tumor inter-fractional set-up displacement. The margin to compensate for tumor variations uncertainties was calculated with various margin calculated recipes published in the exiting literatures.
  
  
  RESULTS
  The means (±standard deviation) of tumor centroid changes were 0.16 (±0.13) cm, 0.22 (±0.15) cm, and 1.37 (±0.81) cm in RL, AP, and SI directions, respectively. The means (±standard deviation) of tumor edge changes were 0.21 (±0.18) cm, 0.50 (±0.23) cm, and 0.19 (±0.44) cm in RL, AP, and SI directions, respectively. The means (±standard deviation) of tumor set-up displacement were 0.03 (±0.24) cm, 0.02 (±0.26) cm, and 0.02 (±0.43) cm in RL, AP, and SI directions, respectively. The PTV margin to compensate for lung cancer tumor variations uncertainties were 0.88, 0.98 and 2.68 cm in RL, AP and SI directions, which were maximal among all margin recipes.
  
  
  CONCLUSIONS
  4DCT and CBCT imaging are appropriate to account for the tumor intra-fractional centroid, boundary variations and inter-fractional set-up displacement. The PTV margin to compensate for lung cancer tumor variations uncertainties can be obtained. Our results show that a conventional 1.0 cm margin in the SI plane dose not suffice to compensate the geometrical variety of the tumor located in lower lobe and adhered to chest wall and diaphragm.
authors.affiliation: Department of Radiation Oncology, The First Affiliated Hospital, Xi'an Jiaotong University of Medical College, Xi'an, Shaanxi, 710061, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology, The First Affiliated Hospital, Xi'an Jiaotong University of Medical College, Xi'an, Shaanxi, 710061, China.
authors.forename: Jing-Lu
authors.initials: JL
authors.lastname: Ma
authors.affiliation: Department of Radiation Oncology, The First Affiliated Hospital, Xi'an Jiaotong University of Medical College, Xi'an, Shaanxi, 710061, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Radiation Oncology, The First Affiliated Hospital, Xi'an Jiaotong University of Medical College, Xi'an, Shaanxi, 710061, China.
authors.forename: Feng-Wen
authors.initials: FW
authors.lastname: Tang
authors.affiliation: Department of Radiation Oncology, The First Affiliated Hospital, Xi'an Jiaotong University of Medical College, Xi'an, Shaanxi, 710061, China. zhang9149@sina.com.
authors.forename: Xiao-Zhi
authors.initials: XZ
authors.lastname: Zhang
mesh_terms: D000328:Adult; D000368:Aged; D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D003964:Diaphragm / Q000473:pathology; D005260:Female; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D016634:Radiosurgery / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D035441:Thoracic Wall / Q000473:pathology
keywords: 4DCT; CBCT; NSCLC; PTV margin; SBRT