Radioactivity in medicine

Detecting Radioactivity 621 17.7 The Discovery of Fission and the Atomic Bomb 627 17.11 Radioactivity in Medicine 632... 

Radioactivity is often perceived as dangerous however, it is also enormously useful to physicians in the diagnosis and treatment of disease. The use of radioactivity in medicine can be broadly divided into isotope scanning and radiotherapy. 

The first use of radioactivity in medicine was the use of radium in the treatment of cancers. Ionizing radiation from radium (or other radionuclide) is focused on the tumour (cancer), and the energy that the radiation carries is used to kill the cancer cells. Sources of fast neutrons have also been used to treat some cancers. Ionizing radiation also kills healthy tissue so it is important that narrow and controlled beams are used. Another technique is to directly inject a radionuclide into the body. This can be done to study the biochemical reactions in the body or for the radionuclide to be concentrated in a particular part of the body and irradiate cancerous tissue. 

CRITICAL THINKING Recall What would be the dangers of using radioactivity in medicine In agriculture ... 

With the production of artificial radioactive substances in 1934. the field of nuclear medicine was established. In 1937, the first radioactive isotope was used to treat a person with leukemia at the University of California at Berkeley. Major strides in the use of radioactivity in medicine occurred in 1946, when a radioactive iodine isotope was successfully used to diagnose thyroid function and to treat hyperthyroidism and thyroid cancer. Radioactive substances are now used to produce images of organs, such as liver, spleen, thyroid gland, kidneys, and the brain, and to detect heart disease. Today, procedures in nuclear medicine provide information about the function and structure of every organ in the body, which allows the nuclear physician to diagnose and treat diseases early. 

Radioactivity in Medicine and Other Applications 940 Key Learning Outcomes 944... 

Radon, sealed in small capsules called seeds , has been used as a radioactive substance in medicine, but is being superseded by more convenient artificially-produced radioisotopes. 

These chemical effects become important in medicine because living systems operate mostly through the reactions of enzymes, which catalyze all sorts of metabolic reactions but are very sensitive to small changes in their environment. Such sensitivity can lead to preferential absorption of some deleterious isotopes in place of the more normal, beneficial ones. One example in metabolic systems can be found in the incorporation of a radioactive strontium isotope in place of calcium. 

Many artificial (likely radioactive) isotopes can be created through nuclear reactions. Radioactive isotopes of iodine are used in medicine, while isotopes of plutonium are used in making atomic bombs. In many analytical applications, the ratio of occurrence of the isotopes is important. For example, it may be important to know the exact ratio of the abundances (relative amounts) of the isotopes 1, 2, and 3 in hydrogen. Such knowledge can be obtained through a mass spectrometric measurement of the isotope abundance ratio. 

In this chapter, we present the atomic perspective of matter, as expressed by atomic theory and the principies of atomic stmcture. We describe the buiiding biocks of atoms eiectrons, protons, and neutrons. Then we show how these interact to form aii the chemicai eiements and expiain which combinations are stabie. Next we describe how atomic masses are reiated to these buiiding biocks. We end the chapter by introducing ions, atoms that have either iost or gained eiectrons. Eurther appiications of radioactive atoms in medicine are found within the chapter. 

The metal is radioactive and does not occur in nature, as the half-life of all isotopes is shorter than 5 million years. It is found in readily isol-able amounts in nuclear reactors. It is an effective "rust-preventer" for iron and steel in special applications. The metastable isotope "Tc has a half-life of only 6 hours and is therefore used as a gamma radiator in medicine (radiation therapy and diagnostics). Of very little commercial importance. 

Nuclear explosions and nuclear power production are the major sources of human radioactivity in the environment. Other sources include radionuclide use in medicine, industry, agriculture,... 

IAEA, Recommendations, Emergency Planning and Preparedness for Accidents Involving Radioactive Materials Used in Medicine, Industry, Research and Teaching, Safety Series 91, International Atomic Energy Agency, Vienna, 1989. 

It has limited use in medicine as a radioactive source. It concentrates in the thyroid gland just like iodine, which makes it a useful radioisotope tracer. 

There is one radioactive isotope of cerium that is used in medicine. It is Ce-l4l, with a half-life of 32,641 days. 

Iodine is an essential nutrient element required for thyroid gland. It is added to salt and to animal feeds for the prevention of goiter. In medicine it is used as a therapeutic reagent for the treatment of various thyroid-related diseases. It also is used as an antiseptic. Radioactive isotopes of iodine are used for treating thyroid cancer, heart diseases including tachycardia, and as a tracer for diagnosing certain diseases. 

Fourth, they are difficult to measure in body fluids. There are very precise ways of measuring very small quantities, in plasma or urine, of almost all conventional medicines and this has made it possible to make the kinetic measurements we have been considering earlier. Some of the techniques for the big protein medicines are not as reliable. For example, one way of tracing a big molecule s progress through the body is to label it with a radioactive tracer. Biopharmaceuticals can be labelled with, for example, radio-iodine (Iodine-125) which can be counted in samples of plasma or urine. However as proteins are similar or identical to normal proteins they can be metabolised and the label can become part of a metabolite or another breakdown product. Counting the iodine radioactivity in this case will not be measuring the parent molecule alone. 

Rosalyn Yalow received the Nobel Prize in medicine in 1977 for developing immunoassay techniques in the 1950s, using proteins labeled with radioactive, 3,l to enable their detection.13 Yalow. a physicist, worked with Solomon Berson, a medical doctor, in this pioneering effort. 

In a technique known as medical imaging, tracers are used in medicine for the diagnosis of internal disorders. Small amounts of a radioactive material, such as sodium iodide, Nal, which contains the radioactive isotope iodine-131, are administered to a patient and traced through the body with a radiation detector. The result, shown in Figure 4.11, is an image that shows how the material is distributed in the body. This technique works because the path the tracer material takes is influenced only by its physical and chemical properties, not by its radioactivity. The tracer may be introduced alone or along with some other chemical, known as a carrier compound, that helps target the isotope to a particular type of tissue in the body. 

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