Imaging of gamma photons emitted from actinium-225 and daughter radionuclides using a small field-of-view GAGG gamma camera

Abstract Actinium-225 (Ac-225) is a promising alpha emitter for radionuclide therapy, with clinical applications expected to start soon. As Ac-225 is introduced for therapeutic use, imaging of Ac-225 and its daughter radionuclides could address challenges such as monitoring radionuclide injection and detecting contamination in clinical settings. While a small field-of-view (FOV) gamma camera could potentially be useful in such scenarios, its efficacy has not yet been thoroughly evaluated. In this study, we assessed the feasibility of using a small FOV gamma camera for imaging Ac-225 and its daughter radionuclides. The gamma camera employed consists of a 10 mm-thick GAGG pixel scintillator block optically coupled to a position-sensitive photomultiplier tube (PSPMT). It is housed within a 2 cm-thick tungsten shield, with a 1 mm diameter pinhole collimator mounted at the front. To image gamma photons from Ac-225 and its daughter radionuclides, we measured 440 keV gamma photons from Bi-213 and 218 keV gamma photons from Fr-221 at varying distances. Using an 8 MBq solution of Ac-225 and its daughter radionuclides positioned 10 cm from the camera, imaging was achieved less than 1 minute, yielding a spatial resolution of approximately 4 mm full width at half maximum (FWHM) and a sensitivity of 1.6 × 10 -6 . We conclude that imaging Ac-225 and its daughter radionuclides is feasible with a small FOV gamma camera, as well as improved sensitivity would enhance its utility for applications such as monitoring radionuclide injections and detecting contamination in clinical environments.