177Lu-based radioligand therapy: A retrospective multicenter analysis to calculate the effective half-life and follow-up dose for the public

The study investigated routinely used radiopharmaceuticals containing lutetium-177 (¹⁷⁷Lu), providing reference values for their effective half-life (T_1/2,eff). So far, no guidelines regarding discharging this patients exist, are essential to ensure radiation protection of the public. This study contributes to the development of binding discharge criteria regarding ¹⁷⁷Lu therapies.This retrospective multicenter study comprised eight nuclear medicine departments. Two commercially available products and two in-house preparations were considered. Radiation measurement methods, in terms of measuring device, setup, and time points were reported, as well as dose rate measurements for T_1/2,eff calculation.The study includes 210 dose rate measurement sets with a mean administered activity of (7149 ± 522) MBq. When only measurements up to 48 h p.i. were taken into account the T_{1/2, eff} were shorter (Pluvicto 1.30 d, Lutathera 1.40 d, ihPSMA 1.45 d, ihRRT 1.97 d) compared to 168 h (1.60 d, 1.89 d, 2.10 d, and 2.85 d, respectively). Differences were statistically significant for all compounds except Lutathera. The 90^th percentile of the T_1/2,eff observed in late measurements (Pluvicto 2.0 d, Lutathera 3.0 d, ihPSMA 3.5 d, ihRRT 4.0 d) can be considered conservative values for discharge calculations.The T_1/2,eff of ¹⁷⁷Lu is considerably shorter than its T_1/2,phy, owing to the pharmacokinetics of the entire molecule. This highlights the need of considering biological clearance mechanisms into calculations of discharge times for patients treated with ¹⁷⁷Lu. If direct measurements are not feasible in clinical routine, reference values support inpatient planning while ensuring radiation protection.