Objectives: Lutetium-177-labeled ethylenediamine-N,N,N',N'-tetrakis (methylene phosphonic acid) (¹⁷⁷Lu-EDTMP), a beta-emitting bone-seeking therapeutic radiopharmaceutical being assessed as an agent for palliation of bone pain, can emit suitable gamma-photons for scintigraphy. This investigation sought to characterize its optimal conditions for whole-body gamma camera imaging in patients.
Materials and methods: Eleven patients with bone metastases underwent whole-body bone scanning using both ⁹⁹mTc-methyl-diphosphonate (⁹⁹mTc-MDP) and ¹⁷⁷Lu-EDTMP (29.4 ± 12.5 MBq/kg BW) utilizing a dual-head camera. For lutetium-177 imaging, two types of collimators, low-energy high-resolution (LEHR) and medium-energy general-purpose (MEGP), and two different peak energies of 113 and 208 keV were used.
Results: The femur-to-muscle uptake ratio (F/M) of ⁹⁹mTc-MDP was 2.69 ± 1.06. For ¹⁷⁷Lu-EDTMP, the significantly highest F/Ms were found at 24 h (12.59 ± 5.73) and 48 h (12.54 ± 5.23) by applying MEGP collimators and collecting the 208 keV photons. In all the combinations of collimator and peak energy, the F/Ms at 24 and 48 h are significantly higher than those at 1 h, except the combination of LEHR collimator and 208 keV peak energy. Lesion-to-normal bone uptake ratios of the ⁹⁹mTc-MDP bone scan and images at the 24 and the 48-h phases of Lu-EDTMP were analyzed. MEGP and 208 keV had significantly higher values in lesion-to-normal bone uptake ratios. The combination of LEHR and 208 keV provided the poorest images.
Conclusion: ¹⁷⁷Lu-EDTMP can provide fine whole-body images with the best results when applying medium-energy collimation and collecting the 208 keV energy photons and alternatively by collecting both 208 and 113 keV photons for higher count statistics. The most appropriate time point for imaging is around 24 h after injection.