926P - Reader variability of PET/CT-based response criteria in DLBCL and association to outcome

Abstract

F-18-fluoro-2-deoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) is essentially recommended for monitoring response to treatment in patients with diffuse large B cell lymphoma (DLBCL) and qualitative interpretation is commonly applied in clinical practice. We aimed to evaluate interobserver agreements of qualitative PET/CT-based response criteria and evaluate predictive value of PET/CT results by each reader for outcome. FDG PET/CT images were obtained for patients with DLBCL at baseline, at interim after 3 cycles of first-line chemotherapy and after completion of chemotherapy. Two nuclear medicine physicians (with 3 and 8 years of experience with FDG PET/CT) blinded to clinical data retrospectively assessed response to chemotherapy using visual qualitative analyses from the International Working Group (IWG) criteria and Lugano classification, respectively. The associations between PET/CT results and progression-free survival (PFS) and overall survival (OS) were assessed using Cox regression analysis. Included were 112 PET/CT images from 59 patients with DLBCL (36 male, 23 female; mean age 53 ± 14 years). In interpretation using binary scoring system from IWG criteria, interobserver agreement was substantial (Cohen's ĸ = 0.76) with absolute agreement consistency of 89%. In interpretation using Deauville five-point scale from Lugano classification, interobserver agreement was moderate (Cohen's weighted ĸ = 0.54) and absolute consistency was 62%. The most common cause of disagreements was discordant interpretation of presence of residual tumor uptake. With mean follow-up period of 88 months, estimated 5-year PFS and OS were 81% and 92%, respectively. Neither interim nor post-treatment PET/CT results by both readers were significantly associated with PFS. Interim PET/CT result using Deauville scale was the only significant factor for OS. Moderate to substantial interobserver agreement was observed for response assessment according to visual analysis and interim PET/CT result could predict OS in patients with DLBCL. Further studies are necessary to validate completely PET/CT-based response criteria and further standardize and consistent PET/CT interpretation.