Jozsef Varga

Department of Nuclear Medicine Institute, University of Debrecen, Debrecen, Hungary

Nuclear medicine applies unsealed radioactive preparations for medical purposes. A preparation is called “unsealed” if it can mix with its environment and may participate in both chemical reactions and biological processes.

Note that radioactive materials are applied in medicine as external and sealed radiation sources as well (Figure 12.1). The cobalt gun has been used extensively as an external source for radiation therapy of tumors (teletherapy). Brachytherapy involves treating a disease by exposure to a radioactive sub­stance. Doctors place a small radioactive source (pellet or seed) in or a short distance from a malignant (e. g., cervical) tumor. Thus, high doses of radiation can be used while reducing the risk of damage to nearby healthy tissue and increasing the likelihood that the tumor is destroyed. The sealed source is then removed so that no radioactive substance is left in the patient’s body. Both teletherapy and brachytherapy belong to radiation therapy rather than nuclear medicine.

The basis of nuclear medicine is the radiotracer technique developed by Gydrgy Hevesy (1885—1966) in 1924; he was awarded the Nobel Prize for chem­istry for this achievement in 1943. The principle is that changing an atom in a molecule for its radioisotope will not significantly change its chemical and bio­logical behavior, while the movement, distribution, and concentration of the mol­ecule (and its derivatives) can be followed by measuring its radiation—even processes in a live human or animal can be studied using external radiation detec­tors. Modern devices allow the detection of such small amounts of the tracer that the function of the organ that we want to study is not affected (in contrast to some X-ray contrast materials). However, biological processes are so complicated that human applications require special considerations; see further details in Sections 12.4 and 12.6.

Nuclear and Radiochemistry. DOI: http://dx. doi. org/10.1016/B978-0-12-391430-9.00012-3

© 2012 Elsevier Inc. All rights reserved.