Delayed post-diuretic (18)F-FDG PET/CT for preoperative evaluation of renal pelvic cancer

Background: Application of (18)F(-)fluorodeoxyglucose positron emission tomography ((18)F-FDG PET) in urological oncology was relatively slowly due to the urinary elimination of (18)F-FDG. We investigated whether delayed post-diuretic (18)F-FDG PET/CT could be used for diagnosing renal pelvic cancer. Methods: 51 patients were included who underwent delayed post-diuretic (18)F-FDG PET/CT for detecting renal pelvic space-occupying lesions. The comparations of delayed PET/CT parameters and clinical characteristics between renal pelvic cancer and benign polyp were investigated. Results: Among the 51 patients, 47 were found to have renal pelvic urothelial carcinoma, and 4 had benign polyp. ROC analysis identified the lesion maximum standardized uptake value (SUVmax) of 6.2 as the optimal cut-off value to distinguish from renal pelvic urothelial carcinoma to benign polyp. With the SUVmax cut-off of 6.2, the sensitivity, and specificity for predicting of renal pelvic urothelial carcinoma were 91.5% (43/47), and 100% (4/4). We also found a significant difference in tumor size between the positive (SUVmax > 6.2) and negative (SUVmax ≤ 6.2) PET groups in renal pelvic cancers. In patients with tumor size < 1.1 cm, the probability of being in the negative PET group was 75%. In such patients, a substantial proportion of renal pelvic cancer demonstrated negative SUVmax similar to that in patients with benign polyp. Conclusion: Delayed (18)F-FDG PET/CT could be used for differentiating renal pelvic cancer from benign polyp. In patients with small tumor size, renal pelvic cancer may present low (18)F-FDG uptake, mimicking the metabolic phenotypes of patients with benign polyp.