A Pilot Study of Photon Counting CT Spectral Analysis Following Pancreatic Adenocarcinoma Resection to Differentiate Local Recurrence From Postsurgical Fibrosis

Objective: To assess photon counting CT (PCCT) spectral parameters in the differentiation of locally recurrent pancreatic adenocarcinoma (PDAC) from benign postsurgical fibrosis after PDAC surgical resection. Methods: Twenty-two patients [12 male, mean±SD: age 71 (8) y] who underwent pancreas protocol PCCT following surgery for PDAC were retrospectively identified. Local recurrence required tissue histopathology or enlarging FDG-avid soft tissue. Nonrecurrence required soft-tissue reduction with stable or decreased CA 19-9. Two blinded radiologists independently drew regions of interest within the surgical bed soft tissue to determine iodine density (I), I normalized to aortic enhancement (I%), fat fraction, and extracellular volume (ECV), which were compared using the Mann-Whitney U test. A P <0.05 indicated statistical significance. The intraclass correlation coefficient was used to assess inter-reader reliability. ROC analysis was performed using mean measurements. Results: On pancreatic parenchymal phase imaging, median [IQR] postcontrast attenuation for patients with nonrecurrence (n=10) and recurrence (n=11) was 32.3 (16.4 to 42.9 HU) and 57.0 (50.2 to 65.5 HU)( P =0.001); enhancement was 23.7 (10.2 to 26.0 HU) and 40.0 (34.4 to 44.5 HU) ( P =0.001); I was 0.6 (0.5 to 0.90 mg/mL) and 1.8 (1.5 to 2.0 mg/mL) ( P <0.001); I% was 8.3 (6.3% to 11.1%) and 34.3 (29.8% to 40.9%) ( P <0.001); and ECV was 5.8 (4.4 to 6.9 mL) and 23.0 (18.0 to 25.8 mL) ( P <0.001), respectively. To differentiate nonrecurrent from recurrent soft tissue, a postcontrast 45.7 HU threshold had 100% sensitivity and 80% specificity [AUC=0.92 (0.80-1.00)]; enhancement of 31.9 HU had 81.8% sensitivity and 100% specificity [AUC=0.98 (0.93-1.00)]; 14.0 mL ECV had 100% sensitivity and 100% specificity [AUC=1.00 (1.00-1.00)]; 1.27 mg/mL I had 90.9% sensitivity and 100% specificity [AUC=0.99 (0.98-1.00)]; and 20.3% I% had 100% sensitivity and 100% specificity (AUC=1.00). Inter-reader agreement was near-perfect (ICCs 0.86 to 0.96). Conclusions: PCCT spectral parameters demonstrated excellent diagnostic performance in differentiating locally recurrent PDAC from postsurgical fibrosis on pancreatic parenchymal phase imaging.