A microdose clinical trial to evaluate [¹⁸F]Florastamin as a positron emission tomography imaging agent in patients with prostate cancer

Purpose: To evaluate the biodistribution of [¹⁸F]Florastamin, a novel ¹⁸F-labelled positron emission tomography (PET) tracer for prostate-specific membrane antigen (PSMA) for the diagnosis of prostate cancer. Methods: PET was performed for five healthy controls and 10 patients with prostate cancer at 0, 10, 30, 70, and 120 mins after injecting 370 MBq of [¹⁸F]Florastamin. The maximum standardised uptake value (SUV_max) was evaluated in the primary tumour. The mean SUV_max (SUV_mean) was evaluated in normal organs. Furthermore, the residence time was evaluated by assessing radioactivity in each organ. The internal radiation dosimetry was calculated using the OLINDA/EXM software. Results: The SUV_max in primary tumours increased with time. A favourable tumour to background ratio was also observed over time. Multiple lymph nodes and bone metastases were also evaluated and showed a similar pattern to SUV_max in the primary tumour. In one patient, a tiny lymph node metastasis was identified using [¹⁸F]Florastamin PET, which was not observed using other modalities, and was histologically confirmed. The highest absorbed dose was observed in the kidney (0.062 ± 0.015 mGy/MBq), followed by the bladder (0.032 ± 0.013 mGy/MBq), liver (0.022 ± 0.006 mGy/MBq), and salivary gland (0.018 ± 0.006 mGy/MBq). The effective dose with a 370 MBq injection of [¹⁸F]Florastamin was 1.81 mSv. No adverse events related to [¹⁸F]Florastamin were reported. Conclusion: We identified a novel PSMA-targeted PET ligand, [¹⁸F]Florastamin, for imaging prostate cancer. [¹⁸F]Florastamin showed a high SUV_max and relatively high tumour to background ratio in both primary tumour and metastatic lesions, which suggests its high sensitivity to detect tumours without any adverse events. Trial registration: KCT0003924 registered at https://cris.nih.go.kr/.