pharmaceuticals. Many radionuclides produced in accelerators cannot be produced by neutron reactions. When they can be, the principal advantage of accelerator-produced radioisotopes is the higher specific activity (more disintegrations per mass of desired element) that can often be achieved than is the case with reactor products. Another not insignificant advantage is that a smaller amount of radioactive waste is generated from charged-particle reactions, especially at low (£30 million electron volts [MeV]) bombarding energies.

Both commercial radionuclide producers and research institutions have added accelerators to their armamentaria. The machines have mostly been compact cyclotrons (Martin, 1979) for industrial use (more than 17 in North America alone) or medical use (Wolf, 1984; Wolf and Jones, 1983). The commercial suppliers of radionuclides each possess two or more cyclotrons for their production needs. The mix of radionuclides produced with these cyclotrons is market driven. As a result a number of radionuclides that are used extensively by the biomedical research community are not available from commercial suppliers because of management decisions associated with profitability. In addition, major North American accelerator installations such as the Brookhaven Linac Isotope Producer (BLIP) facility at Brookhaven National Laboratory (Mausner et al., 1986) and the Los Alamos Meson Physics Facility (LAMPF) at the Los Alamos National Laboratory (Grant et al., 1982) in the United States and the Tri-University Meson Facility (TRIUMF) in Canada (Pate, 1979) have significant radionuclide production programs serving both commercial and research clients.

This chapter reviews the use of selected radionuclides and their availabilities from various sources and how this availability would be affected by an accelerator-based National Biomedical Tracer Facility (NBTF) of the sort suggested by previous advisory groups (Holmes), 1991; Kliewer and Green, 1992; McAfee, 1989; Moody and Peterson, 1989).

CURRENT APPLICATIONS IN MEDICINE AND PHYSICAL AND LIFE SCIENCES

As Table 4-1 illustrates, accelerator-produced radioisotopes, like the reactor-produced radioisotopes reviewed in the previous chapter, are both abundant and versatile. As with the reactor products, their uses fall into the general categories of tracer studies, of which imaging is a special and very important case, and radiotherapy. The general principles involved in the use of radioisotopes in the life sciences as well as some of the history and recent research directions were also provided in the previous chapter, so this section will be limited to a few recent successes.

Perhaps the most widely used accelerator isotope in the medical field is thallium-201 (201Tl). 201Tl imaging of heart muscle is employed during exercise to detect and differentiate between diminished blood flow and tissue death from the loss of blood flow in patients with coronary artery disease. Overall, 201Tl is



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