177Lu-based radioligand therapy: A retrospective multicenter analysis to calculate the effective half-life and...

Area of Science:

• Nuclear Medicine
• Radiopharmacy
• Radiation Oncology

Background:

• Lutetium-177 (177Lu) radiopharmaceuticals are increasingly used in targeted therapies.
• Establishing safe patient discharge criteria is crucial for public radiation protection.
• Current guidelines for discharging patients treated with 177Lu are lacking.

Purpose of the Study:

• To provide reference values for the effective half-life (T1/2,eff) of routinely used 177Lu radiopharmaceuticals.
• To contribute to the development of binding discharge criteria for patients undergoing 177Lu therapies.
• To ensure adequate radiation protection for the public.

Main Methods:

• Retrospective multicenter study across eight nuclear medicine departments.
• Inclusion of commercially available and in-house 177Lu preparations.
• Detailed reporting of radiation measurement methods, including devices, setups, and time points for dose rate measurements.
• Calculation of T1/2,eff using dose rate measurements from 210 sets.

Main Results:

• Effective half-lives (T1/2,eff) varied significantly based on measurement time points (up to 48h vs. 168h post-injection).
• Late measurements (up to 168h) yielded longer T1/2,eff values compared to early measurements (up to 48h) for all compounds.
• The 90th percentile of late measurements provided conservative T1/2,eff values (Pluvicto 2.0d, Lutathera 3.0d, ihPSMA 3.5d, ihRRT 4.0d) suitable for discharge calculations.
• Statistically significant differences in T1/2,eff were observed between early and late measurements for most compounds.

Conclusions:

• The effective half-life (T1/2,eff) of 177Lu radiopharmaceuticals is significantly influenced by pharmacokinetic factors, resulting in shorter values than the physical half-life.
• Biological clearance mechanisms must be considered when calculating discharge times for patients treated with 177Lu.
• Reference values derived from this study can aid in clinical planning and ensure radiation safety when direct measurements are not feasible.