Dual-phase FDG-PET/CT in patients with colorectal cancer: Clinical utility of early delayed scan

Objectives Early delayed scanning (D-1 scan) just after the completion of whole body scanning is easy to perform in clinical settings without additional radiation exposure and repositioning; however, it remains unknown whether the D-1 scan has the same diagnostic performance as the conventional delayed scanning with repositioning (D-2 scan). Our aim was to assess efficacy of D-1 scan in patients with colorectal tumor, comparing with that of D-2 scan.

Methods A total of 36 patients with known or suspected colorectal cancer who had colonoscopy underwent a whole body PET/CT scan at 1-h postinjection (E scan), followed by D-1 and D-2 scans (86±7 min, 126±11 min after injection of FDG, respectively). Diagnostic performance for primary tumors and nodal metastasis was evaluated among E, D-1, and D-2 scan. In addition, clinical usefulness for differentiation was compared between D-1 and D-2 scans for focal uptake seen in the bowel or ureter. Histopathological findings after surgery were used as reference standard.

Results Overall, the detectability of E, D-1, and D-2 scans for primary tumors was equally 95%. The sensitivity, specificity, and accuracy of E scan for nodal metastasis were 39%, 94%, and 67%, respectively, and those of D-1 and D-2 scans were 50%, 94%, and 72%, respectively. Higher diagnostic accuracy for nodal metastasis was obtained by both delayed scans than by E scan. As to the physiological uptake in the bowel or ureter, there were 22 focal uptake areas in the bowel and 44 in the ureter. Of these uptake areas, 10 (45%) and 33 (75%) areas were regarded as physiological in D-1 scan, respectively, by the lack of reproducibility, while 13 (59%) and 43 (98%) areas were accurately interpreted as physiological in D-2 scan, respectively.

Conclusions Our data suggest that the D-1 scan has comparable clinical value with the D-2 scan in patients with colorectal tumor, although more uptake areas caused by physiological process disappeared or moved in the D-2 scan