Objectives Post-chemoradiotherapy (CRT) FDG PET is a useful prognosticator of esophageal cancer. However, debate on the diverse criteria of previous publications preclude worldwide multicenter comparisons, and even a universal practice guide. We aimed to validate a simple qualitative interpretation criterion of post-CRT FDG PET for outcome stratification and compare it with other criteria. Methods The post-CRT FDG PET of 114 patients with esophageal squamous cell carcinoma (ESCC) were independently interpreted using a qualitative 4-point scale (Qual 4PS ) that identified focal esophageal FDG uptake greater than liver uptake as residual tumor. Cohen’s κ coefficient (κ) was used to measure interobserver agreement of Qual 4PS . The Kaplan-Meier method and Cox proportional hazards regression analyses were used for survival analysis. Other criteria included a different qualitative approach (Qual BK ), maximal standardized uptake values (SUV max3.4 , SUV max2.5 ), relative change of SUV max between pre- and post-CRT FDG PET (ΔSUV max ), mean standardized uptake values (SUV mean ), metabolic volume (MV) and total lesion glycolysis (TLG). Results Overall interobserver agreement on the Qual 4PS criterion was excellent (κ: 0.95). Except the Qual BK , SUV max2.5 , and TLG, all the other criteria were significant predictors for overall survival (OS). Multivariable analysis showed only Qual 4PS (HR: 15.41; P = 0.005) and AJCC stage (HR: 2.47; P = 0.007) were significant independent variables. The 2-year OS rates of Qual 4PS (–) patients undergoing CRT alone (68.4%) and patients undergoing trimodality therapy (62.5%) were not significant different, but the 2-year OS rates of Qual 4PS (+) patients undergoing CRT alone (10.0%) were significantly lower than in patients undergoing trimodality therapy (42.1%). Conclusions The Qual 4PS criterion is reproducible for assessing the response of ESCC to CRT, and valuable for predicting survival. It may add value to response-adapted treatment for ESCC patients, and help to decide whether surgery is warranted after CRT.
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