title: Can positron emission tomography (PET) or PET/Computed Tomography (CT) acquired in a nontreatment position be accurately registered to a head-and-neck radiotherapy planning CT?
abstract: OBJECTIVE
  To quantify the uncertainties associated with incorporating diagnostic positron emission tomography/CT (PET/CT) and PET into the radiotherapy treatment-planning process using different image registration tools, including automated and manual rigid body registration methods, as well as deformable image registration.
  
  
  METHODS
  The PET/CTs and treatment-planning CTs from 12 patients were used to evaluate image registration accuracy. The PET/CTs also were used without the contemporaneously acquired CTs to evaluate the registration accuracy of stand-alone PET. Registration accuracy for relevant normal structures was quantified using an overlap index and differences in the center of mass (COM) positions. For tumor volumes, the registration accuracy was measured using COM positions only.
  
  
  RESULTS
  Registration accuracy was better with PET/CT than with PET alone. The COM displacements ranged from 3.2 +/- 0.6 mm (mean +/- 95% confidence interval, for brain) to 8.4 +/- 2.6 mm (spinal cord) for registration with PET/CT data, compared with 4.8 +/- 1.7 mm (brain) and 9.9 +/- 3.1 mm (spinal cord) with PET alone. Deformable registration improved accuracy, with minimum and maximum errors of 1.1 +/- 0.8 mm (brain) and 5.4 +/- 1.4 mm (mandible), respectively.
  
  
  CONCLUSIONS
  It is possible to incorporate PET and/or PET/CT acquired in diagnostic positions into the treatment-planning process through the use of advanced image registration algorithms, but precautions must be taken, particularly when delineating tumor volumes in the neck. Acquisition of PET/CT in the treatment-planning position would be the ideal method to minimize registration errors.
authors.affiliation: Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA, USA.
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Hwang
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Bacharach
authors.forename: Sue S
authors.initials: SS
authors.lastname: Yom
authors.forename: Vivian K
authors.initials: VK
authors.lastname: Weinberg
authors.forename: Jeanne M
authors.initials: JM
authors.lastname: Quivey
authors.forename: Benjamin L
authors.initials: BL
authors.lastname: Franc
authors.forename: Ping
authors.initials: P
authors.lastname: Xia
mesh_terms: D000465:Algorithms; D019788:Fluorodeoxyglucose F18; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy; D006801:Humans; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D047368:Tumor Burden
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18