Preliminary experienceof Al18F-PSMA-11 PET/CT in prostate cancer diagnosis

1358 Introduction: As the commonly used small molecular probes targeting prostate specific membrane antigen (PSMA), 68Ga-PSMA-11 has been used in diagnosis, staging, risk stratification, efficacy evaluation and biochemical recurrence monitoring. However, the widely clinical application was limited by the low popularity of 68Ge/68Ga generator and low yield of Ga-68, in addition, the short half-life makes Ga-68 slightly insufficient in delayed imaging. Accordingly, 18F-labelled analogs are of suitable physicochemical properties, and Al18F-PSMA-11 can prolong the imaging time window of current PSMA-11 PET, potentially adding gain value for detection of metastatic lesions. In this study, Al18F-PSMA-11 was prepared utilizing the Al18F chelation reaction similar with 68Ga-labeling of PSMA-11. Moreover, the clinical application of Al18F-PSMA-11 in PET/CT imaging for PCa patients was summarized as preliminary experience. Methods: Al18F-PSMA-11 was prepared with moderate reaction conditions: for 100 µg PSMA-11 precursor, F-18 ion less than 3.7 GBq was used to react with molar ratio of PSMA-11/AlCl3 = 1, at pH = 5, 60 ℃ for 15 min. Product was purified with tC18 cartridge. For each patch of Al18F-PSMA-11, 2 - 4 subjects were enrolled and injected with interval of one hour, and 20 PCa patients or suspected patients were enrolled so far. PET/CT scan was performed at 50 minutes after injection of Al18F-PSMA-11 (2 MBq/kg body weight) and delayed imaging was performed at 120 minutes post injection. Results: Compared to existing 18F-labelled PSMA-1007 and DCFPyL, the synthetic route of Al18F-PSMA-11 is simpler and of less influence factors. With strict follow of preparation procedures, the labeling rate was high than 60% and radiochemical yield was 42.6 ± 3.5%. For patients (or suspected) with prostate cancer, obviously high radioactivity uptake in multiple bones suggested corresponding bone metastasis. Notably, the SUVmax of metastatic lesions in bones accordantly demonstrated a slight increase in delayed imaging, which was conducive to the confirmation of metastatic lesions and detection of insidious lesions. Although slight defluorination affected the delayed imaging in the diagnosis of bone metastasis, simple differential diagnosis can be made by medical history. A typical Al18F-PSMA-11 PET/CT imaging of patient with prostate cancer was shown in Figure 1, which demonstrated the above statement visually. Conclusions: Al18F-PSMA-11 was of longer observation time window due to its longer half-life than 68Ga-labelled PSMA-11, which was beneficial to the background clearance of metabolic organs so as to detect dormant metastatic lesions. Preliminary data confirmed the feasibility of Al18F-PSMA-11 in detecting lesions with high sensitivity. Larger trials with this PET tracer are expected to further define its capabilities and role in the management of prostate cancer. Acknowledgements: The research was supported by Shanghai Advanced Appropriate Technology Promotion Projects (NO.2019SY029).Figure 1. PET/CT of a patient after radical prostatectomy (male, 70 years old) after injecting Al18F-PSMA-11. (A) imaging at 50 min post injection, (B) delayed imaging. Maximum density projection (a) and PET/CT cross-sectional imaging showed metastatic lesions of multiple ribs (b), sternum and multisegmental vertebrae (c), bilateral iliac bone (d), left femur (e) (arrow). It is notable that the SUVmax of bone metastasis increased from 9.539 to 13.401 for (b), from 19.288 to 21.285 for (c), from 11.534 to 14.511 for (d), from 33.794 to 43.130 for (e).