18F‑FDG PET–CT dual‑time imaging in detection and characterization of recurrent lesions in patients with testicular cancer Ibrahim Mansour Nasr1*, Omnia Mohamed Talaat2, Mahmoud Aly Rezk3 and Ismail Mohamed Ali4 Abstract Background: Testicular cancer is the second most frequent form of male genital tumors. Globally, testicular malignancy has risen over the last forty years. Among malignant testicular tumors, germ cell tumors represent approximately 95% of all tumors. They are classified into seminomatous and non-seminomatous tumors as they differ in clinical features, therapy, and prognosis. Despite the increasing value of whole-body fluorodeoxyglucose positron emotion tomography/computerized tomography (18FDG-PET/CT) for all malignancies, the practical function of this imaging method in testicular germ cell tumors is still unknown. We aim to assess the diagnostic performance of 18FDG- PET/CT dual-time-point imaging (DTPI) in the detection and characterization of recurrent testicular cancer lesions. Results: 18FDG-PET/CT DTPI showed higher specificity (SP) in lesions’ delectability and characterization for local, nodal, and distant lesions than the single time-point imaging (STPI) (97.6%, 93.8%, and 97% versus 95.2%, 68.8%, and 84.8%, respectively) and higher sensitivity (SN) for nodal and distant lesions (97% and 93.8% versus 87.8% and 87.5%, respectively). The mean SUVmaxD and the RI values—not the SUVmaxE—of the malignant lesions were significantly greater than the benign lesions (p 0.001*). Conclusions: 18FDG-PET/CT DTPI and its related indices (SUVmaxD and the RI) are more accurate, sensitive, and specific than the STPI in the characterization of recurrent lesions in testicular cancer patients. Keywords: 18F FDG-PET/CT, Testicular cancer, Recurrence