title: The influence of target and patient characteristics on the volume obtained from cone beam CT in lung stereotactic body radiation therapy.
abstract: OBJECTIVE
  To investigate the influence of tumor and patient characteristics on the target volume obtained from cone beam CT (CBCT) in lung stereotactic body radiation therapy (SBRT).
  
  
  METHODS
  For a given cohort of 71 patients, the internal target volume (ITV) in CBCT obtained from four different datasets was compared with a reference ITV drawn on a four-dimensional CT (4DCT). The significance of the tumor size, location, relative target motion (RM) and patient's body mass index (BMI) and gender on the adequacy of ITV obtained from CBCT was determined.
  
  
  RESULTS
  The median ITV-CBCT was found to be smaller than the ITV-4DCT by 11.8% (range: -49.8 to +24.3%, P<0.001). Small tumors located in the lower lung were found to have a larger RM than large tumors in the upper lung. Tumors located near the central lung had high CT background which reduced the target contrast near the edges. Tumor location close to center vs. periphery was the only significant factor (P=0.046) causing underestimation of ITV in CBCT, rather than RM (P=0.323) and other factors.
  
  
  CONCLUSIONS
  The current clinical study has identified that the location of tumor is a major source of discrepancy between ITV-CBCT and ITV-4DCT for lung SBRT.
authors: Department of Radiation Oncology, Tom Baker Cancer Center, University of Calgary, Calgary, Alberta, Canada. hongwei.liu@albertahealthservices.ca
authors: Hong-Wei
authors: HW
authors: Liu
authors: Rao
authors: R
authors: Khan
authors: Rafael
authors: R
authors: D'Ambrosi
authors: Krista
authors: K
authors: Krobutschek
authors: Zoann
authors: Z
authors: Nugent
authors: Harold
authors: H
authors: Lau
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015992:Body Mass Index; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005260:Female; D056973:Four-Dimensional Computed Tomography; D006801:Humans; D008175:Lung Neoplasms / Q000473:pathology / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D016634:Radiosurgery; D047368:Tumor Burden