Photon-counting CT in pancreatic ductal adenocarcinoma: Feasibility of iodine concentrations for predicting chemotherapy responses

Purpose: To evaluate the feasibility of photon-counting detector (PCD)-CT-derived iodine concentrations (IC) as a predictive factor for tumor volume reductions after short-term chemotherapy for pancreatic ductal adenocarcinoma (PDAC). Methods: We retrospectively enrolled patients with histopathologically proven PDAC who underwent contrast-enhanced PCD-CT before and after first-line chemotherapy between April 2023 and September 2024. IC parameters of pre-treatment tumors on iodine maps were obtained during the pancreatic parenchymal phase (PPP), portal venous phase, and equilibrium phase. Tumor volume reduction rates (TVRR) > 50% and ≤ 50% were classified as responders and non-responders, respectively. IC parameters were compared between the groups using the Mann-Whitney U test. The IC predictive factor (ICPF) was calculated using coefficients obtained from a stepwise logistic regression. Optimal cut-off values were selected using a receiver-operating characteristic analysis. P  < 0.05 indicated a significant difference. Results: Thirty patients (mean age ± standard deviation, 66 ± 11 years; 18 women; 11 responders and 19 non-responders) were evaluated. The median and standard deviation of tumor IC during PPP were significantly higher in responders ( p  = 0.03 and p  = 0.01, respectively). ICPF calculated using median tumor IC during PPP and the tumor diameter at baseline showed the highest AUC of 0.86. Using a cut-off of 0.5, sensitivity and specificity were 72.7 and 94.7%, respectively. Conclusion: Pre-treatment PDAC with higher IC during PPP was associated with higher TVRR after short-term chemotherapy. ICPF has potential as a predictive biomarker to stratify patients with all stages of PDAC into distinct treatment response groups.