Targeted radionuclide therapy using α-emitting radiopharmaceuticals, such as ²¹¹At, has opened new possibilities for treatment of advanced and aggressive cancers. The development of α-emitting radiopharmaceuticals requires understanding of their time-dependent biodistribution which can in principal be achieved by SPECT imaging. However, due to the low abundance of decay emissions of ²¹¹At, imaging-based methods acquiring such information have not found wide-spread use. A different astatine isotope, ²⁰⁹At, accompanied by a greater abundance of X-rays and γ-rays, is more favorable for SPECT imaging. However, the high-energy emissions produced by ²⁰⁹At are highly challenging since they strongly penetrate conventional collimator material and also produce high amounts of scattered photons that may interfere with the low energy photopeaks.

A recently published study in Physics of Medicine and Biology^[1] by Crawford et al. from the University of British Columbia, used the MILabs’ proprietary high-energy cluster collimation^[2] technology for quantitative imaging of ²⁰⁹At. Their aim was to accurately determine Astatine biodistributions with high spatial and temporal resolution. In addition to the high fidelity phantom scans, the in vivo SPECT data was in good agreement with the complementary ex vivo biodistribution studies. This study demonstrates the quantitative strength and superior resolution of VECTor/CT for such novel high-energy isotopes.