Urinary excretion kinetics of [Lu]Lu-PSMA-617.

Introduction: For the implementation of suitable radiation safety measures in [Lu]Lu-PSMA-617 therapy, additional insight into excretion kinetics is important. This study evaluates this kinetics in prostate cancer patients via direct urine measurements.

Methods: Both the short-term (up to 24 h, n = 28 cycles) and long-term kinetics (up to 7 weeks, n = 35 samples) were evaluated by collection of urine samples. Samples were measured on a scintillation counter to determine excretion kinetics.

Results: The mean excretion half-time during the first 20 h was 4.9 h. Kinetics was significantly different for patients with kidney function below or above eGFR 65 ml/min. Calculated skin equivalent dose in case of urinary contamination was between 50 and 145 mSv when it was caused between 0 and 8 h p.i.. Measurable amounts of Lu were found in urine samples up to 18 days p.i..

Conclusion: Excretion kinetics of [Lu]Lu-PSMA-617 is especially relevant during the first 24 h, when accurate radiation safety measures are important to prevent skin contamination. Measures for accurate waste management are relevant up to 18 days.