title: Clinical Assessment of 2D/3D Registration Accuracy in 4 Major Anatomic Sites Using On-Board 2D Kilovoltage Images for 6D Patient Setup.
abstract: To provide a comprehensive assessment of patient setup accuracy in 6 degrees of freedom (DOFs) using 2-dimensional/3-dimensional (2D/3D) image registration with on-board 2-dimensional kilovoltage (OB-2 DkV) radiographic images, we evaluated cranial, head and neck (HN), and thoracic and abdominal sites under clinical conditions. A fast 2D/3D image registration method using graphics processing unit GPU was modified for registration between OB-2 DkV and 3D simulation computed tomography (simCT) images, with 3D/3D registration as the gold standard for 6 DOF alignment. In 2D/3D registration, body roll rotation was obtained solely by matching orthogonal OB-2 DkV images with a series of digitally reconstructed radiographs (DRRs) from simCT with a small rotational increment along the gantry rotation axis. The window/level adjustments for optimal visualization of the bone in OB-2 DkV and DRRs were performed prior to registration. Ideal patient alignment at the isocenter was calculated and used as an initial registration position. In 3D/3D registration, cone-beam CT (CBCT) was aligned to simCT on bony structures using a bone density filter in 6DOF. Included in this retrospective study were 37 patients treated in 55 fractions with frameless stereotactic radiosurgery or stereotactic body radiotherapy for cranial and paraspinal cancer. A cranial phantom was used to serve as a control. In all cases, CBCT images were acquired for patient setup with subsequent OB-2 DkV verification. It was found that the accuracy of the 2D/3D registration was 0.0 ± 0.5 mm and 0.1° ± 0.4° in phantom. In patient, it is site dependent due to deformation of the anatomy: 0.2 ± 1.6 mm and -0.4° ± 1.2° on average for each dimension for the cranial site, 0.7 ± 1.6 mm and 0.3° ± 1.3° for HN, 0.7 ± 2.0 mm and -0.7° ± 1.1° for the thorax, and 1.1 ± 2.6 mm and -0.5° ± 1.9° for the abdomen. Anatomical deformation and presence of soft tissue in 2D/3D registration affect the consistency with 3D/3D registration in 6 DOF: the discrepancy increases in superior to inferior direction.
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA lig2@mskcc.org.
authors.forename: Guang
authors.initials: G
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY, USA.
authors.forename: T Jonathan
authors.initials: TJ
authors.lastname: Yang
authors.affiliation: Center of Medical Physics and Biomedical Engineering, Medical University Vienna, Wien, Austria Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University Vienna, Wien, Austria.
authors.forename: Hugo
authors.initials: H
authors.lastname: Furtado
authors.affiliation: Center of Medical Physics and Biomedical Engineering, Medical University Vienna, Wien, Austria Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Medical University Vienna, Wien, Austria.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Birkfellner
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA.
authors.forename: Åse
authors.initials: Å
authors.lastname: Ballangrud
authors.affiliation: Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, New York, NY, USA.
authors.forename: Simon N
authors.initials: SN
authors.lastname: Powell
authors.affiliation: Department of Medical Physics, Memorial Sloan-Kettering Cancer Center, New York, NY, USA.
authors.forename: James
authors.initials: J
authors.lastname: Mechalakos
mesh_terms: D000005:Abdomen / Q000502:physiology*; D000465:Algorithms; D054893:Cone-Beam Computed Tomography / Q000379:methods; D006257:Head / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D011860:Radiography, Abdominal / Q000379:methods; D013902:Radiography, Thoracic / Q000379:methods; D016634:Radiosurgery / Q000379:methods; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013909:Thorax / Q000502:physiology*; D014057:Tomography, X-Ray Computed / Q000379:methods
keywords: image registration; image-guided radiotherapy; patient setup; rotational correction