Medical applications, technetium

Complexes of technetium in oxidation states ranging from (-1) to (VII) have been prepared chemically and characterized. However, historically only the higher oxidation states (IV), (V) and (VII) have been of major importance in radiopharmaceutical formulations. More recently there has been increased interest in lower oxidation state technetium complexes for medical applications, and the use of ir-acceptor ligands has allowed the preparation of Tc1 complexes which are stable in vivo. The coordination chemistry of technetium has been described in Chapter 42 and recent reviews have been provided by Davison21 and by Schwochau.22 Reviews which relate to medical applications of technetium are given by Jones and Davison,549 Deutsch et al.,20 Deutsch and Barnett,550 Siedel551 and Clarke and Fackler.552 The in vivo chemistry of "mTc chelates has been described by Eckelman and Volkert,553 while the structures of technetium complexes, determined by X-ray diffraction techniques, have been reviewed by Bandoli et ai554... 

The medical applications of nuclear technology range from in vitro and in vivo injections for diagnostic tests to cobalt radiation for cancer therapy. A new medical specialty was created, a family of compact cyclotrons was developed to provide short-lived nuclides, and a sizable industry evolved to produce technetium. Until the nuclear industry was created, technetium had been missing from the chart of chemical elements because the half-life of the most stable member was too short, 21,000 years. Technetium and several other nuclides of importance here are discussed elsewhere in the chapter in connection with their production (see Table 21.19).60,61... 

Technetium is a very suitable radionuclide for medical applications. Owing to its short half-life, radiation doses to the human organism are very low. The problems of protein labeling with technetium have been reviewed by several authors " . The following methods of technetium reduction are used in protein labeling by ascorbate aloneby ascorbate and Fe + by Fe"+ by Sn"+ 84.85,93-9S). trolytic reduction 84. ss). jjy gjjZ+.tartarate by Sn -citrate (Tab. 3). 

Iodine-12 3 concentrates in the thyroid gland, liver, and certain parts of the brain. This radioisotope is used to monitor goiter and other thyroid problems, as well as liver and brain tumors. One of the most useful radioisotopes in medical applications in recent years is an isotope of technetium, an element that does not occur naturally on earth. This isotope, 99m P(, jg produced by the decay of Mo. 

Rdsch F, Qaim SM (1993) Nuclear data relevant to the production of the positron emitting technetium isotope " Tc via the Mo(p,n)-reaction. Radiochim Acta 62 115-121 Rdsch F, Novgorodov AF, Qaim SM (1994) Thermochromatographic separation of Tc from enriched molybdenum targets and its large scale production for nuclear medical application. Radiochim Acta 64 113-120... 

Substitution of a phenyl by the CpRe(CO)3 moiety, bulkier and not easily oxidizable but more lipophilic (log 4-3 for (Z)-30d 3.2 (Z)-OH-tamoxifen) thus produces complexes with an antiestrogenic effect very close to that of OH-tamoxifen itself, an effect that is not influenced by the length of the side chain or by the isomer used. Radioactive forms of these complexes could be envisaged for use either as Re p emitters in radiotherapy, or, since the chemical behavior of technetium is known to be similar to that of rhenium, as technetium y emitters for use in radioimaging. Owing to the very short half-life required in radioisotopes for medical applications, new synthetic routes will have to be found that allow the radioactive entity to be incorporated easily and in good yield at the final step of the synthesis. 

It is astonishing to note that technetium has an important medical application. In 1954 E. J. Baumann and his co-workers [28.10] injected a solution, containing a Tc isotope into rats with tumors. After two hours the Tc concentration in the tumors was 11-30 times higher than in the blood. Since 1964 a diagnostic technique is used in which the isotope 9 Tc with a half-life of six hours is injected in the human body. The radioactive isotope is absorbed in tumors that can later be locaHzed by radioactive detection. The selection of " Tc is justified by the fact that the half-Hfe is low and that the isotope is not a 3-emitter. The isotope can thus perform its medical function with minimal secondary effects for the patient. 

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