| Summary: | <h4>Objectives</h4>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.<h4>Methods</h4>The post-CRT FDG PET of 114 patients with esophageal squamous cell carcinoma (ESCC) were independently interpreted using a qualitative 4-point scale (Qual4PS) 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 Qual4PS. The Kaplan-Meier method and Cox proportional hazards regression analyses were used for survival analysis. Other criteria included a different qualitative approach (QualBK), maximal standardized uptake values (SUVmax3.4, SUVmax2.5), relative change of SUVmax between pre- and post-CRT FDG PET (ΔSUVmax), mean standardized uptake values (SUVmean), metabolic volume (MV) and total lesion glycolysis (TLG).<h4>Results</h4>Overall interobserver agreement on the Qual4PS criterion was excellent (κ: 0.95). Except the QualBK, SUVmax2.5, and TLG, all the other criteria were significant predictors for overall survival (OS). Multivariable analysis showed only Qual4PS (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 Qual4PS(‒) patients undergoing CRT alone (68.4%) and patients undergoing trimodality therapy (62.5%) were not significant different, but the 2-year OS rates of Qual4PS(+) patients undergoing CRT alone (10.0%) were significantly lower than in patients undergoing trimodality therapy (42.1%).<h4>Conclusions</h4>The Qual4PS 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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