title: Evaluating FDG uptake changes between pre and post therapy respiratory gated PET scans.
abstract: OBJECTIVE
  Whole body (3D) and respiratory gated (4D) FDG-PET/CT scans performed pre-radiotherapy (pre-RT) and post-radiotherapy (post-RT) were analyzed to investigate the impact of 4D PET in evaluating 18F-fluorodeoxyglucose (FDG) uptake changes due to therapy, relative to traditional 3D PET.
  
  
  METHODS
  3D and 4D sequential FDG-PET/CT scans were acquired pre-RT and approximately one month post-RT for patients with non-small cell lung cancer (NSCLC). The lesions of high uptake targeted with radiotherapy were identified on the pre-RT scan of each patient. Each lesion on the 3D and each of the five phases of the 4D scan were analyzed using a region of interest (ROI). For each patient the ROIs of the pre-RT scans were used to locate the areas of initial FDG uptake on the post-RT scans following rigid registration. Post-RT ROIs were drawn and the FDG uptake was compared with that of the pre-RT scans.
  
  
  RESULTS
  Sixteen distinct lesions from 12 patients were identified and analyzed. Standardized uptake value (SUV) maxima were significantly higher (p-value <0.005) for the lesions as measured on the 4D compared to 3D PET. Comparison of serial pre and post-RT scans showed a mean 62% decrease in SUV with the 3D PET scan (range 36-89%), and a 67% decrease with the 4D PET scan (range 30-89%). The mean absolute difference in SUV change on 3D versus 4D scans was 4.9%, with a range 0-15% (p-value = 0.07).
  
  
  CONCLUSIONS
  Signal recovery with 4D PET results in higher SUVs when compared to standard 3D PET. Consequently, differences in the evaluation of SUV changes between pre and post-RT plans were observed. Such difference can have a significant impact in PET-based response assessment.
authors.affiliation: Department of Radiation Oncology, Dana-Farber/Brigham and Women's Cancer Center and Harvard Medical School, Boston, MA, USA. maristophanous@mdanderson.org
authors.forename: Michalis
authors.initials: M
authors.lastname: Aristophanous
authors.forename: Yue
authors.initials: Y
authors.lastname: Yong
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Yap
authors.forename: Joseph H
authors.initials: JH
authors.lastname: Killoran
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Allen
authors.forename: Ross I
authors.initials: RI
authors.lastname: Berbeco
authors.forename: Aileen B
authors.initials: AB
authors.lastname: Chen
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D005260:Female; D019788:Fluorodeoxyglucose F18; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods*; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D014057:Tomography, X-Ray Computed
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18