title: Predictive parameters of CyberKnife fiducial-less (XSight Lung) applicability for treatment of early non-small cell lung cancer: a single-center experience.
abstract: OBJECTIVE
  To determine which parameters allow for CyberKnife fiducial-less tumor tracking in stereotactic body radiation therapy (SBRT) for early-stage non-small cell lung cancer.
  
  
  METHODS
  A total of 133 lung SBRT patients were preselected for direct soft-tissue tracking based on manufacturer recommendations (peripherally located tumors ≥1.5 cm with a dense appearance) and staff experience. Patients underwent a tumor visualization test to verify adequate detection by the tracking system (orthogonal radiographs). An analysis of potential predictors of successful tumor tracking was conducted looking at: tumor stage, size, histology, tumor projection on the vertebral column or mediastinum, distance to the diaphragm, lung-to-soft tissue ratio, and patient body mass index.
  
  
  RESULTS
  Tumor visualization was satisfactory for 88 patients (66%) and unsatisfactory for 45 patients (34%). Median time to treatment start was 6 days in the success group (range, 2-18 days) and 15 days (range, 3-63 days) in the failure group. A stage T2 (P=.04), larger tumor size (volume of 15.3 cm(3) vs 6.5 cm(3) in success and failure group, respectively) (P<.0001), and higher tumor density (0.86 g/cm(3) vs 0.79 g/cm(3)) were predictive of adequate detection. There was a 63% decrease in failure risk with every 1-cm increase in maximum tumor dimension (relative risk for failure = 0.37, CI=0.23-0.60, P=.001). A diameter of 3.6 cm predicted a success probability of 80%. Histology, lung-to-soft tissue ratio, distance to diaphragm, patient's body mass index, and tumor projection on vertebral column and mediastinum were not found to be predictive of success.
  
  
  CONCLUSIONS
  Tumor size, volume, and density were the most predictive factors of a successful XSight Lung tumor tracking. Tumors >3.5 cm have ≥80% chance of being adequately visualized and therefore should all be considered for direct tumor tracking.
authors: Radiation Oncology Department, Centre Hospitalier de l'Université de Montréal, Montréal, Quebec, Canada.
authors: Houda
authors: H
authors: Bahig
authors: Marie-Pierre
authors: MP
authors: Campeau
authors: Toni
authors: T
authors: Vu
authors: Robert
authors: R
authors: Doucet
authors: Dominic
authors: D
authors: Béliveau Nadeau
authors: Bernard
authors: B
authors: Fortin
authors: David
authors: D
authors: Roberge
authors: Louise
authors: L
authors: Lambert
authors: Jean-François
authors: JF
authors: Carrier
authors: Edith
authors: E
authors: Filion
mesh_terms: D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D003964:Diaphragm / Q000000981:diagnostic imaging; D005260:Female; D057918:Fiducial Markers; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D008297:Male; D008482:Mediastinum / Q000000981:diagnostic imaging; D018579:Patient Selection; D011859:Radiography; D016634:Radiosurgery / Q000295:instrumentation / Q000379:methods*; D011880:Radiotherapy Planning, Computer-Assisted; D012189:Retrospective Studies; D013131:Spine; D047368:Tumor Burden