Comparing the utility of FDG PET-CT and contrast-enhanced CT in patients with oesophagogastric adenocarcinoma treated with neoadjuvant chemotherapy

BACKGROUND: F]fluoro-D-glucose positron emission tomography-CT (FDG PET-CT) is established in staging oesophagogastric adenocarcinoma. It has an emerging role in assessing response to neoadjuvant chemotherapy (NACT) but its benefits over contrast-enhanced CT (CECT) remain unknown. This study aimed to compare the accuracy of CECT and FDG PET-CT in predicting pathological tumour (ypT) stage, nodal (ypN) stage, pathological treatment response and detecting distant metastases. MATERIALS AND METHODS: Single-centre cohort study of patients with oesophagogastric adenocarcinoma who underwent both CECT and FDG PET-CT before and after NACT. Radiological response was evaluated using the change in oesophageal thickness on CECT and the change in SUVmax for FDG PET-CT. Receiver-operator-characteristic analysis was performed, and the area under the curve (AUC) was calculated to determine the accuracy of CECT and FDG PET-CT to predict pathological stage and treatment response. RESULTS: 105 patients were identified and 92 underwent surgical resection. For inclusion, FDG PET-CT and CECT had to be performed contemporaneously (same scanner, same hospital visit) (n = 66). CECT and FDG PET-CT were comparable for predicting ypT stage (AUC 0.65 vs. 0.62, p = 0.76) and ypN stage (AUC 0.52 vs. 0.53, p = 0.92). FDG PET-CT was a better predictor of pathological tumour response (AUC 0.72 vs. 0.51, p = 0.041). Eight patients had metastatic disease identified on restaging imaging; 8 (100%) by FDG PET-CT; 4 (50.0%) by CECT (p = 0.076). CONCLUSIONS: CECT and FDG PET-CT are clinically useful for restaging following completion of NACT. FDG PET-CT was more accurate at response assessment and identified metastatic disease more frequently. The choice of imaging modality depends on balancing clinical utility with cost and accessibility. KEY POINTS: Question: Is FDG PET-CT or contrast-enhanced CT more accurate in predicting pathological stage and treatment response following completion of neoadjuvant chemotherapy in patients with oesophagogastric adenocarcinoma? FINDINGS: CECT and FDG PET-CT were comparable for predicting pathological stage. FDG PET-CT was a better predictor of tumour response and distant metastases than CECT. CLINICAL RELEVANCE: CECT and FDG PET-CT are both useful for restaging after completion of NACT. FDG PET-CT may be most useful for patients with advanced disease where the likelihood of occult metastases is greatest and response assessment may impact clinical decision-making.