title: Evaluation of Time-Phase Effect on 18F-FDG PET/CT Delineation Methods for Treatment Planning of Nasopharyngeal Carcinoma.
abstract: OBJECTIVE
  Tumor boundary delineation using F-FDG PET/CT is a promising tool for radiotherapy applications, but no consensus has been established regarding the optimal delineation method. Time-phase variability of F-FDG PET/CT imaging frequently affects metabolically active volumes and treatment planning for nasopharyngeal carcinoma (NPC). This study aimed to evaluate the time-phase robustness of 8 methods commonly used for tumor volume delineation in NPC.
  
  
  METHODS
  Twenty patients with biopsy-proven NPC were included and underwent multiple time-phase F-FDG PET/CT imaging. Gross tumor volumes (GTVs), absolute SUV, gradient-based watershed segmentation (GTV-GWT), and anatomic biologic contouring (GTV-ABC) values were determined. The volume of overlap between GTV-CT and the 8 PET-based GTVs was enclosed and the overlap fraction (OF-CT) calculated. Color matrix was used to semiquantify the time-phase differences. Gross tumor volume values obtained with different methods were recorded and compared using paired t test. Time-phase differences of GTVs and SUVmax were compared among groups by analysis of variance with Tukey honest significance tests. The coefficients of variation were computed to assess intrapatient time-phase variability. Similarity coefficient was calculated to evaluate similarity.
  
  
  RESULTS
  Differences were observed between GTVs obtained at different time points using various delineation procedures. Nonsignificantly higher percentages were obtained for GTV-GWT (88.17%) and GTV-ABC (86.98%) compared with other methods, showing their robustness. GTV-40% (0.81-0.88) and GTV-ABC (0.82-0.88) indicated higher similarity with GTV-MRI than the other methods.
  
  
  CONCLUSIONS
  PET/CT-based GTV-ABC between 35 and 55 minutes should be the first choice for NPC treatment planning.
authors: From the *Laboratory for Advanced Interdisciplinary Research, Institutes of Translational Medicine, †Institutes of Intelligent and Molecular Imaging, ‡Division of PET/CT, Department of Radiology, and §Department of Radiation Oncology, the First Affiliated Hospital, Wenzhou Medical University, Wenzhou, China.
authors: Yang-Zong
authors: YZ
authors: Chen
authors: Wen-Feng
authors: WF
authors: Li
authors: Jing-Ying
authors: JY
authors: Wang
authors: Jin-Meng
authors: JM
authors: Wang
authors: Rong-Ying
authors: RY
authors: Ou
authors: Xiang-Wu
authors: XW
authors: Zheng
authors: Yun-Sheng
authors: YS
authors: Xu
authors: Liang
authors: L
authors: Zhao
mesh_terms: D000368:Aged; D002277:Carcinoma; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D000077274:Nasopharyngeal Carcinoma; D009303:Nasopharyngeal Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology; D000072078:Positron Emission Tomography Computed Tomography; D019275:Radiopharmaceuticals; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D047368:Tumor Burden
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18