When hormonal treatment fails to slow the spread of metastatic prostate cancer, patients often face limited therapy options. One promising method is targeted alpha therapy using the radionuclide actinium-225. Radioactive molecules are directed specifically toward cancer cells that express particularly high levels of the surface protein PSMA (prostate-specific membrane antigen), destroying them from within.

For this therapy to work optimally for a given patient, practitioners must first determine how the radioactive drug is distributed within the body and how much reaches the cancer cells. Visualizing the radiotherapeutic agent with a PET (positron emission tomography) scan for only a few hours—for example, with gallium-68 and fluorine-18—is often insufficient for reliable dose planning.