title: A patient alignment solution for lung SBRT setups based on a deformable registration technique.
abstract: OBJECTIVE
  In this work, the authors propose a novel registration strategy for translation-only correction scenarios of lung stereotactic body radiation therapy setups, which can achieve optimal dose coverage for tumors as well as preserve the consistency of registrations with minimal human interference.
  
  
  METHODS
  The proposed solution (centroid-to-centroidor CTC solution) uses the average four-dimensional CT (A4DCT) as the reference CT. The cone-beam CT (CBCT) is deformed to acquire a new centroid for the internal target volume (ITV) on the CBCT. The registration is then accomplished by simply aligning the centroids of the ITVs between the A4DCT and the CBCT. Sixty-seven cases using 64 patients (each case is associated with separate isocenters) have been investigated with the CTC method and compared with the conventional gray-value (G) mode and bone (B) mode registration methods. Dosimetric effects among the tree methods were demonstrated by 18 selected cases. The uncertainty of the CTC method has also been studied.
  
  
  RESULTS
  The registration results demonstrate the superiority of the CTC method over the other two methods. The differences in the D99 and D95 ITV dose coverage between the CTC method and the original plan is small (within 5%) for all of the selected cases except for one for which the tumor presented significant growth during the period between the CT scan and the treatment. Meanwhile, the dose coverage differences between the original plan and the registration results using either the B or G method are significant, as tumor positions varied dramatically, relative to the rib cage, from their positions on the original CT. The largest differences between the D99 and D95 dose coverage of the ITV using the B or G method versus the original plan are as high as 50%. The D20 differences between any of the methods versus the original plan are all less than 2%.
  
  
  CONCLUSIONS
  The CTC method can generate optimal dose coverage to tumors with much better consistency compared with either the G or B method, and it is especially useful when the tumor position varies greatly from its position on the original CT, relative to the rib cage.
authors.affiliation: Department of Radiation Oncology, University of Florida College of Medicine, Gainesville, FL, USA. luboufl@gmail.com
authors.forename: Bo
authors.initials: B
authors.lastname: Lu
authors.forename: Kathryn
authors.initials: K
authors.lastname: Mittauer
authors.forename: Jonathan
authors.initials: J
authors.lastname: Li
authors.forename: Sanjiv
authors.initials: S
authors.lastname: Samant
authors.forename: Roi
authors.initials: R
authors.lastname: Dagan
authors.forename: Paul
authors.initials: P
authors.lastname: Okunieff
authors.forename: Darren
authors.initials: D
authors.lastname: Kahler
authors.forename: Chihray
authors.initials: C
authors.lastname: Liu
mesh_terms: D000465:Algorithms; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000601:surgery*; D056888:Patient Positioning / Q000379:methods*; D010363:Pattern Recognition, Automated / Q000379:methods; D011856:Radiographic Image Enhancement / Q000379:methods; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D016634:Radiosurgery / Q000379:methods*; D011881:Radiotherapy, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D025321:Surgery, Computer-Assisted / Q000379:methods*