Consequences of meta-stable ^177mLu admixture in ¹⁷⁷Lu for patient dosimetry

Lutetium-177 (¹⁷⁷Lu) is a rare earth metal in the lanthanides series which decays by beta emission with a half life of 6.647 days to three excited states and the ground state of¹⁷⁷Hf. When ¹⁷⁷Lu is produced by neutron capture in 176Lu, inevitably an admixture is formed of the long-lived isomer ^177mLu. As its half-life of 160.4 days is so much longer than that of ¹⁷⁷Lu, concerns are raised on its possible enhancement in radiation dose to the patient treated with ¹⁷⁷Lu-DOTA-octreotate. This report evaluates this possible enhancement of the absorbed dose, based on the published pharmacokinetic profile of ¹⁷⁷Lu-DOTA-octreotate and assuming an admixture of 1 kBq ^177mLu /MBq ¹⁷⁷Lu (0.1%).