Interim FDG-PET imaging during neoadjuvant chemoradiotherapy for esophageal cancer: Correlation with pathologic response.

Abstract

175 Background: In this prospective study we evaluated whether changes in metabolic tumor parameters on interim flurodeoxyglucose positron emission tomography (FDG-PET) performed during neoadjuvant chemoradiotherapy (CRT) for esophageal cancer correlates with histopathologic tumor response. Methods: From February 2012 to February 2016, 60 patients with esophageal cancer underwent PET scans before therapy and after 30-36 Gy. Patients who underwent surgery after carboplatin/paclitaxel CRT were eligible for the current analysis. PET metrics of the primary site including maximum standardized uptake value (SUVmax), SUV mean, metabolic tumor volume (MTV), and total lesion glycolysis (TLG) were extracted from the pre-treatment and interim PET based on a manual contour and SUV 2.5 threshold. Patients were called histopathologic responders if they had a complete or near complete tumor response based on the modified Ryan scheme. Relative changes in PET metrics between pre-treatment and interim PET were compared between histopathologic responders and non-responders using the Mann-Whitney test and binary logistic regression. Results: Twenty-six patients were included in the analysis. Adenocarcinoma was the most common histology (n = 23). Eleven patients (42%) had a complete or near complete pathologic response to CRT (histopathologic responders). Changes in PET metrics from pre-treatment to interim PET based on the manual contour were not significantly different between responding and nonresponding tumors. The relative reduction of SUVmax (Mean ± SD) was 38.2% ± 28.4% for histopathologic responders and 27.9% ± 31.4% for non-responders. The relative reduction in MTV, SUV mean and TLG was 36.1% ± 26.2%, 23.5% ± 21.3%, and 49.3% ± 28.3% for histopathologic responders and 28.6% ± 32.0%, 11.8% ± 19.1%, and 33.1% ± 38.5% for histopathologic non-responders, respectively. When analyzed based on the SUV 2.5 threshold there continued to be no significant difference in PET metrics. Conclusions: In this pilot study we observed changes in metabolic tumor parameters on PET performed during CRT for esophageal cancer. However, these changes did not predict for histopathologic responders.