First clinical application of silicon-based [¹⁸F]siPSMA-14 in prostate cancer patients: A proof-of-concept study

Silicon-based ligands are of interest in increasingly used Prostate-specific membrane antigen (PSMA) tracers for prostate cancer (PCa) staging due to their simple and scalable production. Here, we present first data on dosimetry and biodistribution of the novel PSMA-specific tracer [¹⁸F]siPSMA-14.Seven PCa patients referred for PSMA-PET/CT imaging were imaged at 60 and 120 min p.i. (T1 and T3), without forced diuresis, to assess organ absorbed (AD) and effective doses (ED). We matched seven of subsequent 134 patients imaged at 90 min. p. i. (T2) to the initial seven patients according to disease and patient characteristics. SUVs of organs and PCa lesions as well as target-to-non-target ratios (TnTR) were analyzed. Statistical analysis was done using paired t-tests and Mann-Whitney U tests.[¹⁸F]siPSMA-14 dosimetry showed an ED of 1.95E-02±0.25E-02 mSv/MBq with the highest AD in kidneys (1.40E-01±0.41E-01 mGy/MBq). Tracer uptake in lesions (SUVmax±SD) was intense in all patients and increased significantly over time (local lesions (intraprostatic lesions or local recurrences) T1: 10.6±4.5; T3: 14.0±5.9 (p=0.01); metastatic lesions: T1: 17.7±8.9; T3: 20.6±9.4 (p=0.01). PCa uptake at T2 was similar, without significant difference in interindividual comparison in local (T1 to T2: p=0.39; T2 to T3: p=1.0) and metastatic lesions (T1 to T2: p=0.79; T2 to T3: p=0.43).[¹⁸F]siPSMA-14 showed moderate effective doses comparable to other 18F- and 68Ga-labeled PCa tracers even without forced diuresis. Uptake in PCa lesions was high and in line with data for other PSMA specific tracers. This suggests that PET imaging with[¹⁸F]siPSMA-14 is safe and effective even without forced diuresis with the advantage of a simple and scalable production.