title: Factors that affect PERCIST-defined test-retest comparability: an exploration of feasibility in routine clinical practice.
abstract: OBJECTIVE
  The aim of this study was to evaluate the factors affecting the comparability of F-FDG PET/CT scans using the PERSIST criteria for treatment response evaluation in a clinical PET/CT unit.
  
  
  METHODS
  Patients diagnosed with esophageal cancer were assessed for treatment response by comparing 2 F-FDG PET/CT scans, at baseline (PET 1) and 1 month after the end of induction chemoradiation (PET 2). According to the PERCIST recommendations, patients with mean SUV normalized by the lean body mass within reference volume of interest that changed less than 0.3 unit and less than 20% were deemed as comparable. Absolute differences of body weight, blood glucose level, activity of F-FDG, and uptake time between the 2 scans were computed. Binary logistic regression was used to identify the predictive factors, and receiver operating characteristic curves were used for thresholds. P < 0.05 was considered statistically significant.
  
  
  RESULTS
  Sixty-nine subjects were identified. The mean (SD) values at PET 0 and PET 2 were 5.9 (1.04) mmol/L and 6.2 (1.06) mmol/L (P = 0.013), 54.6 (10.0 kg) and 53.3 (10.3 kg) (P = 0.013), 7.7 (1.3 mCi) and 7.6 (1.5 mCi) (P = 0.349), as well as 74.2 (12.4) minutes and 73.0 (12.3) minutes (P = 0.539), for blood glucose level, body weight, injected activity, and uptake time, respectively. Seventeen (24.6%) failed to match the PERCIST-defined comparability criteria. Case-based discrepancies (mean [SD]) were 0.76 (0.62) mmol/L, 3.4 (2.9) kg, 0.8 (0.7) mCi, and 11.7 (9.8) minutes for blood glucose, body weight, injected activity, and uptake time, respectively, of which only uptake time significantly affected comparability (P = 0.046; odds ratio, 1.06; 95% confidence interval, 1.00-1.12), with a limit of 2.2-minute discrepancy identified as the requirement for 100% comparability.
  
  
  CONCLUSIONS
  Uptake time had the strongest effect on PERCIST-defined comparability. Therefore, for response assessment scans, reference to initial scans for determination of optimal uptake time is recommended.
authors.affiliation: From the *Department of Diagnostic Radiology, †Division of Esophageal and Upper Gastrointestinal Surgery, Department of Surgery, The University of Hong Kong, Queen Mary Hospital, Hong Kong, SAR.
authors.forename: Hui
authors.initials: H
authors.lastname: Yuan
authors.forename: Daniel King Hung
authors.initials: DK
authors.lastname: Tong
authors.forename: Varut
authors.initials: V
authors.lastname: Vardhanabhuti
authors.forename: Pek-Lan
authors.initials: PL
authors.lastname: Khong
mesh_terms: D000328:Adult; D000368:Aged; D004938:Esophageal Neoplasms / Q000000981:diagnostic imaging*; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18