Radiohalogens

Radiohalogens are radioactive isotopes of the halogen elements—fluorine, chlorine, bromine, iodine and astatine. They share chemical properties with their stable counterparts, allowing them to form halide ions or covalent bonds and to be incorporated into organic molecules for diagnostic or therapeutic purposes.

Among the most important in medicine are fluorine-18 (half-life about 109.8 minutes, positron emitter) used in positron emission tomography (PET) imaging (for example in [18F]FDG); iodine-123 (about 13.2 hours, gamma emitter) used in SPECT imaging and thyroid studies; iodine-125 (about 59.4 days) used in research and some brachytherapy applications; iodine-131 (about 8 days) used in therapy for thyroid diseases; and astatine-211 (about 7.2 hours, alpha emitter) studied for targeted alpha therapy. Bromine-76 and chlorine-36 are less common clinically but illustrate the range of half-lives and decay modes found among radiohalogens.

Production and handling: radiohalogens are produced in nuclear reactors or cyclotrons by irradiation of suitable target nuclei, followed by chemical separation to isolate the specific halogen isotope. They are then incorporated into radiopharmaceuticals or other compounds through established halogenation chemistry, enabling delivery to desired tissues or biological targets.

Applications and safety: the primary use of radiohalogens is in diagnostic imaging and radiotherapy. Fluorine-18 and iodine isotopes are widely used for imaging, while iodine-131 and astatine-211 are employed in therapeutic contexts or investigated for targeted treatments. Because their decay emits ionizing radiation, proper shielding, dosimetry, handling protocols, and regulatory oversight are required to minimize patient and worker exposure.