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 [ 18 F]Florastamin, a novel 18 F-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 [ 18 F]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 [ 18 F]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 [ 18 F]Florastamin was 1.81 mSv. No adverse events related to [ 18 F]Florastamin were reported. Conclusion We identified a novel PSMA-targeted PET ligand, [ 18 F]Florastamin, for imaging prostate cancer. [ 18 F]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/ .