There has been increasing interest during the past 10 years in the use of 177Lu for radionuclide-based radiotherapy for certain types of cancers. Accurate administrations of drugs using this radionuclide require accurate standards against which instrumentation used in the clinics and radiopharmacies can be calibrated. Several new 177Lu-based radiotherapy drugs are being investigated worldwide, which will cause an even greater need for such standards.
Lutetium-177 decays with three primary branches (Eβmax = 176 keV, 385 keV, and 498 keV) and has two reasonably strong γ-rays at 113 keV and 208 keV, making it suitable for analysis using a variety of techniques, including coincidence counting.
The only previous comparison of 177Lu that has been carried out was a bilateral comparison (BIPM-R(II)-K1.177Lu) conducted between the NIST and the Physikalisch-Technische Bundesanstalt (PTB) in 2000. In that case, both laboratories were able to submit ampoules to the International Reference System (SIR) and report activity values based on liquid scintillation counting using the Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT)/NIST efficiency tracing method. The results indicated a difference of about 1.4 % in the SIR equivalent activity. The short half-life of the 177Lu did not allow for follow-up studies to be performed.continued