More than one hundred radio-isotopes have been used to assist in a wide variety of diagnostic tests and treatment protocols. The use of radio-isotopes is convenient because they can emit gamma radiation, have a short half-life, and are eliminated from the body shortly after the completion of the diagnostic test or treatment. Radiodiagnostic protocols include:
1. Radioactive tracers are added to the blood stream to enable us to monitor the movement of biochemical components in the human body.
2. Iodine 131, a beta emitter, is used for the treatment of overactive thyroids and also for detecting internal hemorrhages.
3. Diagnostic techniques:
Diagnostic techniques in nuclear medicine use radioactive tracers which emit gamma rays from within the body. These tracers are generally short-lived isotopes linked to chemical compounds which permit specific physiological processes to be scrutinized. They can be given by injection, inhalation, or orally.
An instrument called a gamma camera produces an image of the distribution of radioactivity in an organ and by using this in conjunction with a computer, the functioning of the organ can be closely monitored.
4. In Positron Emission Tomography (PET) scan, which is "a more precise and sophisticated technique" for detecting cancerous growth in the human body:
A positron-emitting radionuclide is introduced, usually by injection, and accumulates in the target tissue. As it decays it emits a positron, which promptly combines with a nearby electron resulting in the simultaneous emission of two identifiable gamma rays in opposite directions. These are detected by a PET camera and give very precise indication of their origin. PET's most important clinical role is in oncology, with fluorine-18 as the tracer, since it has proven to be the most accurate non-invasive method of detecting and evaluating most cancers. It is also well used in cardiac and brain imaging.
Major therapeutic uses of radio-isotopes are:
1. Cobalt 60, an intense gamma emitter is often used in cancer therapy through direct irradiation.
2. Phosphorous 32, another beta emitter is often injected intravenously for treatment of leukemia.
3. Plutonium 238, an alpha emitter is used as a long lasting low level power source for pacemakers to regulate heart action.
4. Caesium 137, encased in a biologically inert material container, is inserted into body cavities like cervix or rectum to treat cancers in these regions effectively. Intense gamma radiation from the radioisotope kills cancer cells locally, while the beta emissions are shielded by the container walls.
5. Gold 198 or Iridium 192 wires can be inserted as implant for treatment of cancer in the tongue.
The list seems endless. A more detailed account can be obtained in the reference link given here.
The future of radiotherapy is probably the tagging of a monoclonal antibody for a specific cell followed by the injection of the radioactive complex into the blood. The monoclonal antibodies then bind selectively to the tumour cells thereby concentrating the initial low dose to a level that destroys the tumour.