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.