Predicting pathological response to neoadjuvant chemoradiotherapy in resectable and borderline resectable pancreatic ductal adenocarcinoma: a comparative study of 18F-FLT and 18F-FDG PET

This study aimed to compare the utility of 3’-deoxy-3’-¹⁸F-fluorothymidine (FLT) positron emission tomography (PET) and 2-deoxy-2-¹⁸F-fluoro-D-glucose (FDG) PET in predicting pathological response to neoadjuvant chemoradiotherapy (nCRT) in patients with resectable and borderline resectable pancreatic ductal adenocarcinoma (PDAC), and retrospectively evaluated 21 patients who underwent FLT and FDG PET before and after nCRT. The maximum standardised uptake value (SUVmax) of the primary tumour was measured pre- and post-nCRT, and the percentage reduction in SUVmax (%ΔSUVmax) was calculated. Pathological response was assessed using the Evans grading system, with Grades I–IIa defined as non-responders and Grades IIb–IV as responders. Mann-Whitney U tests and receiver operating characteristic (ROC) analyses were performed. Three patients with blood glucose levels ≥ 200 mg/dL at pre-nCRT FDG PET were excluded from FDG PET analysis. Surgical specimens classified nine patients as responders and 12 as non-responders. SUVmax_pre-nCRT did not differ significantly between groups for either modality. SUVmax_post-nCRT was significantly lower in responders for both FLT (P = 0.001) and FDG (P = 0.009) PET. A significant %ΔSUVmax difference was observed only with FLT PET (P = 0.002). Areas under the curve for predicting response to nCRT were: FLT SUVmax_post-nCRT (0.90), FLT %ΔSUVmax (0.89), and FDG SUVmax_post-nCRT (0.86). FLT PET demonstrated comparable performance to FDG PET in assessing response to nCRT in resectable and borderline resectable PDAC, with potential as a complementary or alternative imaging modality in neoadjuvant settings given its independence from glycaemic status and biological proliferation specificity.