title: Deformable versus rigid registration of PET/CT images for radiation treatment planning of head and neck and lung cancer patients: a retrospective dosimetric comparison.
abstract: BACKGROUND
  The purpose of this study is to evaluate the clinical impact of using deformable registration in tumor volume definition between separately acquired PET/CT and planning CT images.
  
  
  METHODS
  Ten lung and 10 head and neck cancer patients were retrospectively selected. PET/CT images were registered with planning CT scans using commercially available software. Radiation oncologists defined two sets of gross tumor volumes based on either rigidly or deformably registered PET/CT images, and properties of these volumes were then compared.
  
  
  RESULTS
  The average displacement between rigid and deformable gross tumor volumes was 1.8 mm (0.7 mm) with a standard deviation of 1.0 mm (0.6 mm) for the head and neck (lung) cancer subjects. The Dice similarity coefficients ranged from 0.76-0.92 and 0.76-0.97 for the head and neck and lung subjects, respectively, indicating conformity. All gross tumor volumes received at least 95% of the prescribed dose to 99% of their volume. Differences in the mean radiation dose delivered to the gross tumor volumes were at most 2%. Differences in the fraction of the tumor volumes receiving 100% of the radiation dose were at most 5%.
  
  
  CONCLUSIONS
  The study revealed limitations in the commercial software used to perform deformable registration. Unless significant anatomical differences between PET/CT and planning CT images are present, deformable registration was shown to be of marginal value when delineating gross tumor volumes.
authors: Department of Medical Physics, BC Cancer Agency-Vancouver Island Centre, 2410 Lee Avenue, V8R 6V5 Victoria, British Columbia, Canada. dominique.fortin@bccancer.bc.ca.
authors: Dominique
authors: D
authors: Fortin
authors: Parminder S
authors: PS
authors: Basran
authors: Tanya
authors: T
authors: Berrang
authors: David
authors: D
authors: Peterson
authors: Elaine S
authors: ES
authors: Wai
mesh_terms: D000368:Aged; D002289:Carcinoma, Non-Small-Cell Lung / Q000473:pathology / Q000532:radiotherapy*; D006258:Head and Neck Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008175:Lung Neoplasms / Q000473:pathology / Q000532:radiotherapy*; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012189:Retrospective Studies; D012984:Software; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden