title: Towards clinical implementation of ultrafast combined kV-MV CBCT for IGRT of lung cancer : Evaluation of registration accuracy based on phantom study.
abstract: OBJECTIVE
  Combined kV-MV cone-beam CT (CBCT) is a promising approach to accelerate imaging for patients with lung tumors treated with deep inspiration breath-hold. During a single breath-hold (15 s), a 3D kV-MV CBCT can be acquired, thus minimizing motion artifacts and increasing patient comfort. Prior to clinical implementation, positioning accuracy was evaluated and compared to clinically established imaging techniques.
  
  
  METHODS
  An inhomogeneous thorax phantom with four tumor-mimicking inlays was imaged in 10 predefined positions and registered to a planning CT. Novel kV-MV CBCT imaging (90° arc) was compared to clinically established kV-chest CBCT (360°) as well as nonclinical kV-CBCT and low-dose MV-CBCT (each 180°). Manual registration, automatic registration provided by the manufacturer and an additional in-house developed manufacturer-independent framework based on the MATLAB registration toolkit were applied.
  
  
  RESULTS
  Systematic setup error was reduced to 0.05 mm by high-precision phantom positioning with optical tracking. Stochastic mean displacement errors were 0.5 ± 0.3 mm in right-left, 0.4  ± 0.4 mm in anteroposterior and 0.0 ± 0.4 mm in craniocaudal directions for kV-MV CBCT with manual registration (maximum errors of no more than 1.4 mm). Clinical kV-chest CBCT resulted in mean errors of 0.2 mm (other modalities: 0.4-0.8 mm). Similar results were achieved with both automatic registration methods.
  
  
  CONCLUSIONS
  The comparison study of repositioning accuracy between novel kV-MV CBCT and clinically established volume imaging demonstrated that registration accuracy is maintained below 1 mm. Since imaging time is reduced to one breath-hold, kV-MV CBCT is ideal for image guidance, e.g., in lung stereotactic ablative radiotherapy.
authors: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Haus 4, Ebene 0, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Germany. anna.arns@medma.uni-heidelberg.de.
authors: Anna
authors: A
authors: Arns
authors: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Haus 4, Ebene 0, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Germany.
authors: Manuel
authors: M
authors: Blessing
authors: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Haus 4, Ebene 0, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Germany.
authors: Jens
authors: J
authors: Fleckenstein
authors: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Haus 4, Ebene 0, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Germany.
authors: Dzmitry
authors: D
authors: Stsepankou
authors: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Haus 4, Ebene 0, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Germany.
authors: Judit
authors: J
authors: Boda-Heggemann
authors: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Haus 4, Ebene 0, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Germany.
authors: Anna
authors: A
authors: Simeonova-Chergou
authors: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Haus 4, Ebene 0, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Germany.
authors: Jürgen
authors: J
authors: Hesser
authors: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Haus 4, Ebene 0, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Germany.
authors: Frank
authors: F
authors: Lohr
authors: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Haus 4, Ebene 0, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Germany.
authors: Frederik
authors: F
authors: Wenz
authors: Department of Radiation Oncology, University Medical Center Mannheim, University of Heidelberg, Haus 4, Ebene 0, Theodor-Kutzer-Ufer 1-3, 68167, Mannheim, Germany.
authors: Hansjörg
authors: H
authors: Wertz
mesh_terms: D017076:Computer-Aided Design; D054893:Cone-Beam Computed Tomography / Q000295:instrumentation*; D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011856:Radiographic Image Enhancement / Q000379:methods; D011879:Radiotherapy Dosage; D061089:Radiotherapy, Image-Guided / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D018511:Systems Integration
keywords: Cone-beam computed tomography; Image-guided radiotherapy; Lung neoplasms; Patient positioning; kV-MV imaging