High Sensitivity In-Vivo 225Ac Imaging of Mice with a Compton Camera
Abstract
Targeted alpha therapy with 225Ac is a promising modality for cancer treatment, as recently shown in pre-clinical and clinical trials. Achieving a precise understanding of the biokinetics of 225Ac radiopharmaceuticals is critical to leverage their potential in the clinic. Although this is typically achieved via gamma-ray imaging experiments, such imaging is very challenging for 225Ac due to the extremely low injected activities (<37 kBq), the unfavorable gamma-ray branching ratios (<26%), and the complicated decay chain. Standard SPECT with collimation struggles to achieve quality images and accurate quantification in pre-clinical experiments. In this work, we propose Compton imaging as an alternative solution for this problem. We leverage a commercial CZT Compton camera to achieve in-vivo imaging of 225Ac in mice at therapeutic activities below the microcurie. We compared the sensitivity of a single-head Compton imaging system with that of a standard collimated gamma camera to be 4.7 times greater for 213Bi and 7.5 for 221Fr. We successfully imaged 225Ac daughter biodistributions of 221Fr and 213Bi in a mouse in vivo with only 30 minutes scan time and a single bed position. Performance can be further improved by using more detector heads and via system optimization. Comparison between in-vivo and ex-vivo will be presented and discussed.
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