A Pilot Study to Assess Pancreatic Adenocarcinoma Treatment Response With Iodine Density From Photon Counting CT.

Abstract

Objective: To assess photon counting CT iodine density as a marker of histopathologic treatment response after neoadjuvant chemotherapy in patients with pancreatic ductal adenocarcinoma.

Materials and methods: A retrospective PACS search identified 21 pancreatic ductal adenocarcinoma patients [14 men; mean (SD) age: 64 (10) y] who underwent neoadjuvant chemotherapy and pancreatic photon counting CT 2 months before resection from April 11, 2022 to February 2, 2024. The histopathologic treatment response grade was the reference standard. Freehand regions-of-interest measurements were drawn independently by 2 radiologists as large as possible within the mass on pancreatic parenchymal phase images. Attenuation, iodine density, and iodine density normalized to the aorta were recorded. Mann-Whitney U test was used to compare attenuation, iodine density, and normalized iodine density for responders (pathologic grade 1, 2) versus nonresponders (grade 3). Receiver operating characteristic curves were created, and optimal thresholds were determined with Youden's index. A P<0.05 indicated statistical significance.

Results: Thirteen of 21 (61.9%) patients showed pathologic treatment response. Iodine density for nonresponders and responders was mean (SD) 0.47 (0.23) mg/mL and 1.20 (0.75) mg/mL, respectively (P=0.005). Normalized iodine density for nonresponders and responders was 7.6 (5.5)% and 22.5 (16.0)%, (P=0.006). Attenuation for nonresponders and responders was 56.5 (10.9) HU and 70.6 (17.7) HU, (P=0.04). Upon receiver operating characteristic analysis, an iodine density threshold of 0.65 mg/mL had 77% sensitivity and 88% specificity (AUC=0.86), and a normalized iodine density threshold of 10.1% had 77% sensitivity and 88% specificity (AUC=0.86) for treatment response. A 61.8 HU threshold had 77% sensitivity and 75% specificity (AUC=0.78).

Conclusions: Elevated iodine density correlates with pancreatic ductal adenocarcinoma histopathologic treatment response with high specificity. Photon counting CT iodine density may be used as a marker of histopathologic treatment response.