Coded aperture and Compton imaging for the development of ²²⁵ Ac-based radiopharmaceuticals

Targeted alpha-particle therapy (TAT) has great promise as a cancer treatment. Arguably the most promising TAT radionuclide that has been proposed is ²²⁵ Ac. The development of ²²⁵ Ac-based radiopharmaceuticals has been hampered due to the lack of effective means to study the daughter redistribution of these agents in small animals at the preclinical stage.

The ability to directly image the daughters, namely ²²¹ Fr and ²¹³ Bi, via their gamma-ray emissions would be a boon for preclinical studies. That said, conventional medical imaging modalities, including single photon emission computed tomography (SPECT) based on nonmultiplexed collimation, cannot be employed due to sensitivity limitations.

As an alternative, we propose the use of both coded aperture and Compton imaging with the former modality suited to the 218-keV gamma-ray emission of ²²¹ Fr and the latter suited to the 440-keV gamma-ray emission of ²¹³ Bi.

This work includes coded aperture images of ²²¹ Fr and Compton images of ²¹³ Bi in tumor-bearing mice injected with ²²⁵ Ac-based radiopharmaceuticals.

These results are the first demonstration of visualizing and quantifying the ²²⁵ Ac daughters in small animals through the application of coded aperture and Compton imaging.