**1. Introduction**

136 12 Chapters on Nuclear Medicine

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Medicine in clinical diagnosis and treatment, Livingstone C; 1209-1221,

Nuclear medicine practices rely on the use of radiopharmaceuticals, for diagnosis and therapy purposes. Their use is based on the incorporation in the human body through a medical procedure: intravenous injection, ingestion, or inhalation. The quality of the administration procedure is tightly influenced by the following determining factors: the administration of the right activity to the patient, such as prescribed by the medical doctor, and the quality of the radiopharmaceutical product. The full control of these parameters is obtained by using high quality measurement equipment and following well established procedures for the measurement and application of the radiopharmaceutical.

The radiopharmacy units, the measurement equipment providers and the nuclear medicine units can fulfill these requirements only by using calibrated instrumentation and following validated measurement methods. The technical support is offered by the Radionuclide Metrology Laboratories (RML) which can assure the continuity of the metrological traceability chain of measurement up to the highest, primary radioactivity standards. The metrological traceability and its chain are defined by the document: *"BIPM, JCGM 200:2008 – International vocabulary of metrology – Basic and general concepts and associated terms (VIM)",* as:


From these definitions one can deduce the role of the RMLs: to develop activity standards, to validate them in relation with the International System of Units (SI) and to disseminate them as radioactive standard sources and solutions, or calibration services to the implied entities.

This chapter of the book presents the following aspects:


Role of the Radionuclide Metrology in Nuclear Medicine 139


Table 1 presents a list of radionuclides used for the production of radiopharmaceuticals, in terms of production mode, nuclear decay data and *E/A*. Referring the *E/A* value, it is strongly dependent on the type of radiopharmaceutical, diagnostic procedure and the age of the patient; only for a rough information, the comparative dose values due to the ingestion of radionuclides by the adult public (ICRP 1996c) are given, in order to emphasize the

The values of *E/A* from Table 1 are based on the Medical Internal Radiation Dose (MIRD) model, while at present time the calculation models use the "voxel phantom", defined in international documents as *"a computational anthropomorphic phantom based on medical tomographic images where the anatomy is described by small three dimensional volume elements (voxels) specifying the density and the atomic composition of the various organs and tissues of the human body"*. A special attention is paid to the radionuclide 99mTc, used nowadays in about 80% of the world diagnosis procedures. Its widespread use is due to several properties: i. Its committed effective dose of activity unit is *E/A* =0.022mSv/MBq and the corresponding doses in the diagnostic procedures are generally within the limits (1 -2)

mSv, due to the short half-life and to the small content of low energy electrons. ii. The 140.5 keV quanta are emitted with a high intensity, being situated near the

iii. It can be extracted from a 99Mo generator (2.75 d,) a reasonable life time for transport and use for a period of two weeks, or can be prepared in a pharmaceutical unit and

iv. It is carrier free and due to its position in the Mendeleev Table, the VII-b group, with 7 valence electrons, it can be used for binding in various chemical compounds, with

**Radionuclide (targeted) therapy principle**. The incorporated radiopharmaceutical is localized in the biological formation to be destroyed by irradiation. In this case, the entire energy of particles must be transferred to the matter. Consequently, low range radiations, such as: alpha particles and electrons - beta radiation, Auger and conversion electrons, are useful. This is the reason for which alpha, strong beta with high energy, electron capture and conversion decaying radionuclides are used. Lately a special attention is given to the beta-gamma triangular decay scheme radionuclides, with strong beta and weak gamma – ray energies and intensities, due to the ability to be monitored by a gamma camera during the treatment procedure. The half life can be from hours up to tens of days, in order to assure the prescribed dose to the biological formation to be destroyed. The choice of the radionuclides takes into account their chemical properties, as well as their radiations range in the tissue, which must be comparable with the dimensions of the biological formation to be destroyed. Table 2 presents a list of therapeutical radionuclides, with their modes of

strong dependence of the dose on the characteristics of the nuclear decay scheme.

inside the body. The most used radionuclide is 18F.

maximum detection efficiency of the usual scintillators.

delivered to the neighboring hospitals in the same day.

production, nuclear decay parameters and the tissue range.

various valence states.
