Internal Targeting with Nuclear Medicine
There have been many great advances in the diagnosis and treatment of disease over the past few decades. Some of the most important have come in the field of nuclear medicine.
Nuclear medicine is the science of putting radioactive isotopes in the body in order to target specific areas of the body. Its most widespread use is in the field of diagnostic imaging. Radiation has been used for a long time to do diagnostic studies. Nearly everyone is familiar with X-rays where radiation is sent through the body to reveal the underlying skeletal structure. With nuclear medicine, the radioactive materials generating high energy emissions are actually placed inside the body. They thus radiate outward instead of through the body.
One of the reasons that this is useful is that one can target certain regions of the body with the agent. For example, a monoclonal antibody can be combined with a radioactive material to target a specific type of tissue to isolate it from the rest of the body. That part of the body will then appear "hot" on the scan allowing one to isolate the morphology of that particular tissue from the surrounding tissue. This leads to entire classes of functionally based scans.
The imaging agents used in nuclear medicine are referred to as radiopharmaceuticals, and the specialists who practice this field of medicine are referred to as radiologists. A treatment center has to be very careful with the use of radiopharmaceuticals due to their internalization in the body and potential excretion from it.
The ability to target specific types of tissues with chemical compounds is the primary advantage of nuclear medical diagnostics. This same targeting ability can be used for treatment. This type of treatment is referred to as interventional nuclear medicine. For example, a monoclonal antibody can be made against a specific tumor antigen and coupled with a radioactive agent. The theory is that the antibody will selectively bind to the tumor and bring the radionuclide in proximity with it, thereby killing the tumor mass. Zevalin and Bexxar have been used in such a manner to treat severe cases of lymphoma.
Biological targeted therapies like this are only in their infant stages. Most other radiopharmaceuticals target tissues more generally in terms of their metabolic activity. For example, fluorodeoxyglucose (FDG) is a radioactive mimic of glucose that is used to isolate areas of high glucose uptake. Since cancer cells are highly metabolically active, this agent is used in whole body PET scans to attempt to detect any abnormal growths in the body.
As molecular biologists discover new ways of targeting specific tissue types, both the diagnostic and therapeutic applications of nuclear medicine should increase dramatically the next several decades.