Targeted alpha therapy (TAT) is attracting attention as a new approach to cancer treatment. Alpha rays, with their short range and high energy, act directly on the DNA of cancer cells, causing double-strand breaks and inducing cell death, while minimizing the impact on surrounding healthy tissue. This allows for precise damage to target cells, making it an effective treatment for refractory and metastatic cancers. Already, alpha radiation therapies, including radium-223 (223RaCl2, trade name: Xofigo) for castration-resistant prostate cancer with bone metastases, have been put into practical use, and improvements in treatment outcomes have been reported. In addition, clinical trials for prostate cancer, such as PSMA-targeted therapy using actinium-225 (225Ac), are progressing, and the high therapeutic effect is attracting attention. Japan is leading the world in research using astatine-211 (211At), a short-lived alpha-emitting nuclide with a half-life of 7.2 h [1] (Fig. 129.1).