Applications of Radionuclides in Medicine

In the area of human health, radioactivity is a double-edged sword. On one hand, radioactivity substances can make people sick and even kill them. On the other hand, radioactive substances can be used to diagnose and cure disease. Let s look first at the use of radionuclides in the diagnosis of disease. 

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Application of radionuclides in life sciences is of the greatest importance, and the largest single user of radionuclides is nuclear medicine. Shortly after the discovery of Ra in 1898 by Marie Curie and its subsequent isolation from pitchblende in amounts of 0.1 to 1 g, the finding that this element was useful as a radiation source led to the first application of radionuclides in medicine. In 1921, de Hevesy investigated the metabolism of lead in plants by use of natural radioisotopes of Pb. 

Radioactive contamination can result from either expected or accidental release of radionuclides during the treatment of uranium ores, the operation of nuclear reactors, the processing of burnt fuel elements from nuclear reactors, or the application of radionuclides in medicine, research, industry, and agriculture, as well as from radioactive fallout from the atmosphere. 

Radiochemistry is defined as the chemical study of radioactive elements, both natural and artificial, and their use in the study of chemical processes (Random House Dictionary, 1984). Operationally, radiochemistry is defined by the activities of radiochemists, that is, (a) nuclear analytical methods, (b) the application of radionuclides in areas outside of chemistry, such as medicine, (c) the physics and chemistry of the radioelements, (d) the physics and chemistry of high-activity-level matter, and (e) radiotracer studies. We have dealt with several of these topics in Chapters 4, 13, 15, and 16. In this chapter, we will discuss the basic principles behind radiochemical techniques and some details of their application. 

Sometimes high or well-defined specific activities are required, for instance in the case of the application of radionuclides or labelled compounds in medicine, or as tracers in other fields of research. 

Application of short-lived radionuclides has the advantage that the activity vanishes after relatively short periods of time. This aspect is of special importance in nuclear medicine. Short-hved radionuclides may be produced by irradiation in nuclear reactors or by accelerators, but their supply from in-adiation facilities requires matching of production and demand, and fast transport. These problems are avoided by application of radionuclide generators containing a longer-lived mother nuclide from which the short-hved daughter nuclide can be separated. 

Labelled compounds have found broad application in various fields of science and technology. A great variety of labelled compounds are applied in nuclear medicine. The compounds are produced on a large scale as radiopharmaceuticals in cooperation with nuclear medicine, mainly for diagnostic purposes and sometimes also for therapeutic application. The study of metabolism by means of labelled compounds is of great importance in biology. More details on the application of radionuclides and labelled compounds in medicine and other areas of the life sciences will be given in chapter 19. 

Applications include the use of radionuclides in geo- and cosmochemistry, dating by nuclear methods, radioanalysis, the use of radiotracers in chemical research, Mossbauer spectrometry and related methods, the use of radionuclides in the life sciences, in particular in medicine, technical and industrial applications and investigations of the behaviour of natural and man-made radionuclides, in particular actinides and fission products, in the environment (geosphere and biosphere). Dosimetry and radiation protection are considered in the last chapter of the book. 

The development of applications of radioactive materials in research, industry, medicine, and agriculture, as well as the growth of nuclear power engineering programs, led to increasing amounts and varieties of radionuclides in the environment. This, together with the development of the nuclear sciences, has created the demand for proper analytical methods of monitoring radionuclides in the environment. 

Annex 3 (Manufacture of Radiopharmaceuticals) is the only part of the GMP framework entirely dedicated to radiopharmaceuticals [10]. Preparation of radiopharmaceuticals using authorised generators and kits is excluded from this Annex. The production of radionuclides in reactors and cyclotrons is a physical process and is regarded as a non-GMP activity. Annex 3 describes general GMP principles (quality assurance, personnel, premises and equipment, documentation, production, quality control, reference and retention samples, distribution) in relation to radiopharmaceuticals. As with other medicinal products, other GMP annexes may be applicable, for instance Annex 1 Manufacture of Sterile Medicinal Products [11]. 

Radiopharmaceutical Kits Radiopharmaceutical kits are nonradioactive ( cold ) products containing the sterile ingredients needed to prepare the final radiopharmaceutical. Immediately before administration to the patient, the radionuclide is added. From the point of licensing, these semimanufactured products are defined as radiopharmaceuticals, as they have no other application in medicine [2],... 

The task of quantitative and effective separation of small amounts of radionuclides has appreciably enhanced the development of modem separation techniques. High radionuclide purity is of great importance for application in nuclear medicine as well as for sensitive measurements. In this context, impurities of long-lived radionuclides arc of particular importance, because their relative activity increases with time. For example, if the activity of Sr is only 0.1% of that of Ba after fre.sh separation, it will increase to 11.5% in three months. 

Generator-produced radionuclides are also introduced into compounds suitable for specific applications, in particular in medicine. For Instance, " TcOj eluted from a Mo/ Tc radionuclide generator can be introduced into organic compounds by various chemical procedures that can be performed by use of special kits which allow easy handling. 

Nowadays, nuclear medicine has become an indispensible section of medical science, and the production of radionuclides and labelled compounds for application in nuclear medicine is an important branch of nuclear and radiochemistry. The development of radionuclide generators made short-lived radionuclides available at any time for medical application. New imaging devices, such as single photon emission tomography (SPET) and positron emission tomography (PET) made it possible to study local biochemical reactions and their kinetics in the living human body. 

The production of short-lived positron emitters has been described in section 12.2. By interaction with electrons, the positrons are annihilated and two y-ray photons of 511 keV each are emitted simultaneously in opposite directions. By measuring these photons by means of a suitable arrangement of detectors, exact localization of the radionuclides in the body is possible. This is the basis of positron emission tomography (PET), which has found broad application in nuclear medicine. The most frequently used positron emitters are listed in Table 19.2. They are preferably produced by small cyclotrons in the hospitals or nearby. 

Other accelerator-produced radionuclides are also used in nuclear medicine (Table 19.2). One of the most important radionuclides in this group is This radioisotope of iodine has more favourable properties than it emits only y radiation and its relatively short half-life is more appropriate for medical application. Its production is described in section 12.1. Suitable accelerators for the generation of protons of relatively high energy, and transport facilities, are needed. 

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