Post-chemoradiotherapy FDG PET with qualitative interpretation criteria for outcome stratification in esophageal squamous cell carcinoma

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.