tained in a solution, is then adsorbed onto an alumina (Al2O3) column that is contained in cylinders that are about the diameter of a large pencil. The columns are shipped to radiopharmacies and hospitals in radiation-shielded cartridges known as technetium generators (Figure 2.1).

The Mo-99 in the generators decays with about a 66-hour half-life to Tc-99m. The Tc-99m is typically recovered by passing a saline solution through the alumina column in the generator, a process known as eluting the generator. The saline removes the Tc-99m but leaves the Mo-99 in place. A technetium generator can be eluted several times a day for about a week before it needs to be replaced4 with a fresh generator (Figure 2.2).

There are numerous Tc-99m kits5 for producing radiopharmaceuticals to examine the brain, kidney, heart, bone, liver, and lung. Table 2.1 provides a selected list of Tc-99m labeled radiopharmaceuticals in use today. The list is not intended to be exhaustive but to illustrate the range of diseases and conditions where Tc-99m based diagnostic imaging is useful. Figure 2.3 provides examples of images that can be obtained from diagnostic imaging procedures.

Because of its relatively short half-life (66 hours), Mo-99 cannot be stockpiled for use. It must be made on a weekly or more frequent basis to ensure continuous availability. The processes for producing Mo-99 and technetium generators and delivering them to customers are tightly scheduled and highly time dependent. An interruption at any point in the production, transport, or delivery of Mo-99 or technetium generators can have substantial impacts on patient care, as discussed in Chapter 4.

Mo-99 PRODUCTION PROCESS

There are two primary approaches for producing the medical isotope Mo-99, as described in Appendix D: fission of U-235, which produces Mo-99 and other medically important isotopes such as I-131 and Xe-133, and neutron capture by Mo-98 to produce Mo-99. For the reasons described in Appendix D, the committee dismissed neutron capture as a viable process for producing Mo-99 in the quantities needed to meet U.S. or global demand for Mo-99. None of the four global producers of Mo-99 (Chapter 1) use the neutron capture method to produce Mo-99 because of its inefficiencies. However, this process can be used to make smaller

4

The technetium generator is replaced after about a week because it loses its elution efficiency and also because the Tc-99m can become contaminated with Mo-99 from the column. The latter process is referred to as Mo-99 breakthrough. After it is replaced, the old generator may continue to be used for research that does not involve human subjects.

5

Kits are composed of all of the required chemicals (e.g., the pharmaceutical agent, chelating compound, and saline solution) for formulating the radiopharmaceutical to which Tc-99m is added.



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