Compton Imaging of Ac-225 In Pre-clinical Phantoms With a 3D-positioning CZT Camera
Abstract
225Ac-based radiopharmaceuticals for targeted alpha therapy (TAT) have shown positive outcomes in recent clinical trials and preclinical studies, and it has emerged as a promising solution for future cancer treatments. Small-animal in-vivo imaging is critical to better understand 225Ac radiopharmaceuticals biokinetics and to accelerate evaluation and discovery of new 225Ac radiopharmaceuticals. However, gamma-ray imaging of 225Ac and its daughters is challenging due to the extremely low injected activities, the low branching ratios of the emitted $\gamma $ rays, and their broad range of energies. State-of-the-art scanners for single-photon emission computed tomography (SPECT) have sensitivity limitations when imaging such low activities, and imaging sessions of several hours are necessary, precluding in-vivo studies. We propose Compton imaging as an alternative to traditional SPECT imagers in order to enable a higher sensitivity and to decrease the minimum imageable activities of current systems. In this study, we explore a 3D-positioning cadmium zinc telluride (CZT) camera (M400, H3D) to achieve highly sensitive Compton imaging of 225Ac daughters at both high-energy (440 keV from 213Bi) and low-energy gamma rays (218 keV from 221Fr). The Compton sensitivity of the imaging system with a source as close as possible from the detector (7 mm) were 1014(33) cps/MBq and 467(23) cps/MBq for 213Bi and 221Fr, respectively. We studied the response of the camera using 225Ac point…
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