Delayed ¹⁸F FDG PET/CT Imaging in the Assessment of Residual Tumors after Transurethral Resection of Bladder Cancer

Background Delayed fluorine 18 (¹⁸F) fluorodeoxyglucose (FDG) PET/CT is used to diagnose bladder cancer. However, it remains difficult to determine whether a lesion with abnormal ¹⁸F FDG uptake is tumor residue or recurrence or if it is an inflammatory reaction in patients with bladder cancer after oncologic treatment. Purpose To determine the diagnostic performance of delayed ¹⁸F FDG PET/CT in the differentiation of residual tumors from postoperative inflammatory reactions in patients with bladder cancer after initial transurethral resection of bladder tumor (TURBT). Materials and Methods A retrospective clinical study between January 2015 and April 2018 was performed in 79 patients with bladder cancer who had undergone ¹⁸F FDG PET/CT within 1 month after initial TURBT. After PET/CT, all patients underwent a second surgery within 2 weeks to confirm the histologic nature of the suspicious lesion and to remove residual tumors. Uni- and multivariable analysis were used to identify predictive factors for residual bladder tumors. Results A total of 79 patients (61 men, 18 women; mean age, 63 years ± 11 [standard deviation]) were enrolled in this study. A total of 98 lesions was studied, 64 (65.3%) of which were residual tumors after initial TURBT. When compared with inflammatory reactions, residual tumors had higher mean standardized uptake value (SUV_mean) (mean, 5.8 ± 2.0 vs 9.3 ± 5.4; P < .001), higher maximum standardized uptake value (SUV_max) (mean, 15.5 ± 9.8 vs 22.2 ± 13.6, P = .01), and greater lesion thickness (mean, 9.6 mm ± 4.1 vs 17.9 mm ± 11.1, P < .001) at ¹⁸F FDG PET/CT. SUV_mean (odds ratio [OR], 1.2; 95% confidence interval [CI]: 1.0, 1.5; P = .049) and lesion thickness (OR, 1.2; 95% CI: 1.0, 1.3; P = .006 or OR, 1.2; 95% CI: 1.1, 1.3; P = .001) were identified as independent predictors for residual tumors with multivariable logistic regression analysis. On the basis of the threshold values of SUV_mean and lesion thickness, we revealed a prediction rate of 37.5% (17 of 47), 85.4% (26 of 29), and 98.3% (21 of 22) for residual tumors in low-, moderate-, and high-risk subgroups, respectively. Conclusion Use of fluorine 18 fluorodeoxyglucose PET/CT to differentiate lesions after transurethral resection of bladder tumor indicates that higher mean standardized uptake values and greater lesion thickness are predictive factors for residual tumors in patients with bladder cancer after oncologic treatment. Published under a CC BY 4.0 license.