**1. Introduction**

Prostate carcinoma (PC) is the second most common tumor in men worldwide. Its predicted mortality rate in the European Union for 2020 is 10/100,000, which has decreased by 7.1% since 2015 due to advances in screening and treatment of the disease [1]. In particular, the early detection of PC and the early initiation of therapy have contributed significantly to the reduced mortality rate.

Current conventional imaging for PC, such as multiparametric magnetic resonance imaging (MRI) and computed tomography (CT), show limitations, especially in the primary diagnosis of lymph node metastases (LNM) [2]. Other diagnostic methods, such as positron emission tomography (PET), usually in combination with CT, are therefore used in PC diagnostics. The prospective, randomized multicenter study called "proPSMA" showed that in patients with biopsy-proven high-risk PC, PET/CT with prostate-specific

**Citation:** Hoffmann, M.A.; Müller-Hübenthal, J.; Rosar, F.; Fischer, N.; von Eyben, F.E.; Buchholz, H.-G.; Wieler, H.J.; Schreckenberger, M. Primary Staging of Prostate Cancer Patients with [ 18F]PSMA-1007 PET/CT Compared with [68Ga]Ga-PSMA-11 PET/CT. *J. Clin. Med.* **2022**, *11*, 5064. https:// doi.org/10.3390/jcm11175064

Academic Editors: Arnoldo Piccardo and Francesco Fiz

Received: 29 July 2022 Accepted: 23 August 2022 Published: 29 August 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

membrane antigen (PSMA PET/CT) imaging is superior to conventional combined CT and bone scintigraphy for primary staging of PC metastases [2,3]. The transmembrane protein PSMA is particularly overexpressed in higher-grade prostate cancer cells and offers an optimal target for radiolabeled ligands [4]. One of the world's most commonly used PSMA inhibitors is the 68Gallium(68Ga)-labeled [68Ga]Ga-HBED-CC-PSMA, also named [ 68Ga]Ga-PSMA-11, which was also used in the Hofmann study [2,3,5]. Several other PSMA ligands for labeling with 68Ga and 18Fluorine (18F) have been developed in recent years. In particular, the 18F-labeled tracers will be further explored [2,4]. 18F has a half-life of 110 min, whereas 68Ga has one of 68 min, which is an advantage for the delivery of radiopharmaceuticals. An additional advantage of 18F-labeled PSMA ligands is optimal positron energy, which enables higher resolution of PET images with refined image quality [2,4,6]. Currently, according to the European Association of Urology (EAU), European Association of Nuclear Medicine (EANM), European Society for Radiotherapy & Oncology (ESTRO), European Society of Urogenital Radiology (ESUR), the International Society of Urological Pathology (ISUP), and the International Society of Geriatric Oncology (SIOG) there are few comparative data on 18F- with 68Ga-labeled PSMA tracers in a clinical setting [2].

The goal of this study is to investigate and compare [18F]PSMA-1007 PET/CT (18F-PSMA) and [68Ga]Ga-PSMA-11 PET/CT (68Ga-PSMA) for the primary staging of PC patients and to distinguish between low- and intermediate-risk versus (vs.) high-risk PC as well as between low- and intermediate-favorable risk vs. intermediate-unfavorable and high-risk PC, using the best maximum standardized uptake value (SUVmax) cut-off value to identify clinically significant PC foci.
