title: Nonrigid image registration for head and neck cancer radiotherapy treatment planning with PET/CT.
abstract: OBJECTIVE
  Head and neck radiotherapy planning with positron emission tomography/computed tomography (PET/CT) requires the images to be reliably registered with treatment planning CT. Acquiring PET/CT in treatment position is problematic, and in practice for some patients it may be beneficial to use diagnostic PET/CT for radiotherapy planning. Therefore, the aim of this study was first to quantify the image registration accuracy of PET/CT to radiotherapy CT and, second, to assess whether PET/CT acquired in diagnostic position can be registered to planning CT.
  
  
  METHODS
  Positron emission tomography/CT acquired in diagnostic and treatment position for five patients with head and neck cancer was registered to radiotherapy planning CT using both rigid and nonrigid image registration. The root mean squared error for each method was calculated from a set of anatomic landmarks marked by four independent observers.
  
  
  RESULTS
  Nonrigid and rigid registration errors for treatment position PET/CT to planning CT were 2.77 +/- 0.80 mm and 4.96 +/- 2.38 mm, respectively, p = 0.001. Applying the nonrigid registration to diagnostic position PET/CT produced a more accurate match to the planning CT than rigid registration of treatment position PET/CT (3.20 +/- 1.22 mm and 4.96 +/- 2.38 mm, respectively, p = 0.012).
  
  
  CONCLUSIONS
  Nonrigid registration provides a more accurate registration of head and neck PET/CT to treatment planning CT than rigid registration. In addition, nonrigid registration of PET/CT acquired with patients in a standardized, diagnostic position can provide images registered to planning CT with greater accuracy than a rigid registration of PET/CT images acquired in treatment position. This may allow greater flexibility in the timing of PET/CT for head and neck cancer patients due to undergo radiotherapy.
authors: Academic Unit of Radiology, University of Sheffield, Sheffield, UK. r.ireland@sheffield.ac.uk
authors: Rob H
authors: RH
authors: Ireland
authors: Karen E
authors: KE
authors: Dyker
authors: David C
authors: DC
authors: Barber
authors: Steven M
authors: SM
authors: Wood
authors: Michael B
authors: MB
authors: Hanney
authors: Wendy B
authors: WB
authors: Tindale
authors: Neil
authors: N
authors: Woodhouse
authors: Nigel
authors: N
authors: Hoggard
authors: John
authors: J
authors: Conway
authors: Martin H
authors: MH
authors: Robinson
mesh_terms: D019788:Fluorodeoxyglucose F18; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D020266:Radiotherapy, Conformal / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18