Observer Variation in Interpreting 18F-FDG PET/CT Findings for Lymphoma Staging

Many studies demonstrate a high accuracy for PET in staging lymphoma, but few assess observer variation. This study quantified agreement for staging lymphoma with PET/CT. Methods: The PET/CT images of 100 patients with lymphoma who had been referred for staging were reviewed by 3 experienced observers, with 2 observers reviewing each series a second time. Ann Arbor stage and individual nodal and extranodal regions were assessed. Weighted κ (κw) and intraclass correlation coefficient were used to compare ratings. Results: Intra- and interobserver agreement was high for Ann Arbor stage (κw = 0.79–0.91), number of nodal regions involved (intraclass correlation coefficient, 0.83–0.93), and presence of extranodal disease (κ = 0.74–0.86). High agreement was also observed for all nodal regions (κw > 0.60) except hilar (κw = 0.56–0.82) and infraclavicular (κw = 0.14–0.55). Lower agreement was observed for bowel involvement (κw = 0.37–0.71). Conclusion: Experienced observers had a high level of agreement using PET/CT for lymphoma staging, supporting its use as a robust noninvasive staging tool. Further research is needed to evaluate observer variability for restaging during and after chemotherapy.