Bismuth

²¹²Bi and ²¹³Bi (with half-lives of 1 h and 0.76 h, respectively) are both used in medicine for radioimmunotherapy as bismuth-labeled monoclonal antibodies to treat cancer cells from melanoma (skin cancer) (Fig. IUPAC.83.1) and ovarian cancer [559]. Figure 4.83.2 compares the biologic effect of ¹³¹I and ²¹³Bi using a specific monoclonal antibody, B-B₄, coupled to ²¹³Bi by a chelating agent (a substance that can form multiple bonds to a single metal ion). ²¹³Bi is a mixed alpha and beta emitter with a half-life of 0.76 h. The primary mode of decay is by beta emission to the very short-lived alpha emitter ²¹³Po. The 8.4 MeV alpha particle emitted by ²¹³Po has a path length of 76 μm in human tissue and is responsible for its cytotoxic effects (toxic to living cells). ²¹³Bi is produced from a series of alpha particle decays beginning with ²²⁵Ac, which is a pure alpha emitter with a half-life of 10 days. A schematic of the Institute for Transuranium Elements (ITU) Standard ²²⁵Ac/ ²¹³Bi Radionuclide Generator is shown in Fig. IUPAC.83.3. ²¹²Bi has been used for radioimmunotherapy of leukemia and for targeting the vascular endothelial cells (thin layer of simple squamous cells that forms the interface between circulating blood or lymph and the remainder of the vessel wall) of tumors [560].