Metallic radionuclides: Applications in diagnostic and therapeutic nuclear medicine

Nuclear Medicine is a medical modality that utilizes radioactivity (radiopharmaceutical) to diagnose and treat disease. Radiopharmaceuticals contain a component which directs the radionuclide to the desire physiological target. For diagnostic applications, these nuclides must emit a gamma ray that can penetrate the body and can be detected externally while for therapeutic purposes nuclides are preferred that emit beta particles and deliver highly localized tissue damage. Ga-67 citrate is employed to detect chronic occult abscesses, Hodgkin's and non-Hodgkin's lymphomas, lung cancer, hepatoma and melanoma and localizes in these tissues utilizing iron-binding proteins. (201)Thallous chloride, a potassium analogue, used to diagnosis coronary artery disease, is incorporated in muscle tissue via the Na+-K+-ATPase. In-111 labeled autologous white blood cells, used for the diagnosis of acute infections and inflammations,takes advantage of the white cell's role in fighting infections. (111)Ln is incorporated in other radiopharmaceuticals e.g. polyclonal Igc, OncoScint CR/OV, OctreoScan and Myoscint by coupling diethylenetriaminepentaacetic acid, a chelate, covalently to these molecules. OncoScint CR/OV and Myoscint localize by antigen antibody interactions while OctreoScan is taken up by malignant cells in a receptor based process. Polyclonal IgG may share some localization characteristics with Ga-67. Sr-89, a pure beta emitter, is used for palliation of bone pain due to metastatic bone lesions. Bone salts [Ca(PO)(4)] are increased in these lesions and this radionuclide is taken up similarly to Ca2+. Re-186 and Sm-153 bound to polydentate phosphonate chelates are used similarly and follow the phosphate pathway in lesion incorporation.