Simultaneous dual-isotope SPECT/CT with 99mTc- and 111In-labelled albumin microspheres in treatment planning for SIRT

Objectives To investigate simultaneous dual-isotope SPECT/CT with two differently radioisotope-labelled albumin-microsphere fractions for treatment planning of hepatic radioembolisation. Methods In addition to 99m Technetium-labelled albumin microspheres (commercially available), we performed labelling with 111 Indium. Binding stability of 111 Indium-labelled microspheres was tested in vitro and in vivo in mice. Simultaneous dual-isotope SPECT/CT imaging was validated in an anthropomorphic torso phantom; subsequently, dual-isotope SPECT/CT was performed under in-vivo conditions in pigs ( n = 3) that underwent transarterial injection of 99m Technetium- and 111 Indium-labelled microspheres in the liver (right and left hepatic artery, respectively), in both kidneys and in the gluteal musculature. In total, n = 18 transarterial injections were performed. Results In-vitro testing and in-vivo studies in mice documented high binding stability for both 99m Technetium-labelled and 111 Indium-labelled microsphere fractions. In phantom studies, simultaneous dual-isotope SPECT/CT enabled reliable separation of both isotopes. In pigs, the identified deposition of both isotopes could be accurately matched with intended injection targets (100 %, 18/18 intended injection sites). Furthermore, an incidental deposition of 99m Technetium-labelled microspheres in the stomach could be correlated to the test injection into a right hepatic artery. Conclusion Simultaneous dual-isotope SPECT/CT after transarterial injection with 99m Technetium- and 111 Indium-labelled microspheres is feasible. Thus, it may offer additional, valuable information compared to single 99m Technetium-labelled albumin examinations. Key Points • Simultaneous dual-isotope SPECT/CT with 111 In- and 99m Tc-labelled albumin microspheres is feasible. • Differentiation of two microsphere fractions after transarterial injection is possible. • The origin of an extra-hepatic microsphere deposition can be correlated to the corresponding artery. • This technique could reduce the setup time for selective internal radiation treatment.