Delayed18F-fluoro-2-deoxy-D-glucose positron emission tomography scan for differentiation between malignant and benign lesions in the pancreas

Abstract

BACKGROUND Positron emission tomography (PET) using ¹⁸F‐fluoro‐2‐deoxy‐D‐glucose (FDG) has been used for the evaluation of various tumors, but accumulation in inflammatory lesions makes it a controversial modality. The aim of this study was to investigate the usefulness of delayed scanning in differentiation between malignant and benign lesions in the pancreas. METHODS Forty‐seven patients with suspected pancreatic carcinoma were studied by FDG‐PET. All patients received approximately 370 megabequerels of FDG after a transmission scan, and an emission scan was performed 1 hour and 2 hours later for all patients. A subset of 19 patients was also scanned at 3 hours postinjection. The standardized uptake value (SUV) was determined, and the retention index was calculated by dividing the increase in the SUV between 1 hour and 2 hours postinjection by the SUV at 1 hour postinjection. RESULTS Of 27 malignant lesions, the SUVs of 22 lesions increased at 2 hours postinjection, whereas the FDG uptake in 17 of 20 benign lesions decreased. The SUVs at 3 hours postinjection were higher than those at 2 hours postinjection in 9 of 14 malignant lesions and in 2 of 5 benign lesions. Malignant lesions showed a higher retention index than benign lesions (mean ± standard deviation: 12.36 ± 13.37 and −7.05 ± 17.28, respectively; P < 0.0001). Applying an SUV of 2.5 at 1 hour postinjection with the cut‐off value for the differentiation between malignant and benign lesions caused one false negative result and seven false positive results, with a diagnostic accuracy of 83.0% (39 of 47 patients). However, combining the retention index with the SUV obtained at 2 hours postinjection provided a higher diagnostic accuracy (91.5%; 43 or 47 patients) than the SUV alone. The false negative rate remained constant when the retention index was taken into account. Images at 3 hours postinjection usually were unhelpful in differentiating further between malignant lesions and benign lesions. CONCLUSIONS The current data suggest that delayed FDG‐PET scanning at 2 hours postinjection may contribute to differentiation between malignant and benign lesions in the pancreas. Cancer 2000;89:2547–54. © 2000 American Cancer Society.