 Nuclear medicine plays a growing role in diagnosis and therapy. Radioisotopes are a crucial component of the radiopharmaceuticals that are used routinely in the clinics for the non-invasive diagnosis and treatment of various diseases. These radiopharmaceuticals are specific biological molecules tagged (or 'labelled') with medical radioisotopes. They are also called 'tracers', because they only need to be administered in very small quantities (traces) due to the high sensitivity provided by nuclear radiation.
Radioisotopes also allow the tracing of biological processes. This is performed by the detection of gamma-rays in a process called Single Photon Emission Computed Tomography (SPECT).
Technetium-99m (the m stands for metastable energy state) is currently the most widely used radioactive tracer isotope for medical imaging and therapy in Nuclear Medicine. The technetium isotope 99mTc is unusual in that it has a half-life of 6.03 hours; this is extremely long for an electromagnetic decay - more typical would be 10-16 seconds. The dominant decay mode gives the useful gamma ray of 140 keV which is sufficient to escape from the human body.
The currently most frequently used method to produce 99Mo is through the fission of 235-U in a nuclear reactor. 99mTc is produced by bombarding 98Mo with neutrons; followed by the harvesting and processing steps which end in a 99Mo/99mTc generator that is transported from the reactor site to the various international sites where the final product is distributed to hospitals. The resultant 99Mo decays with a half-life of 66 hours to the meta-stable state of Tc. This process permits the production of 99mTc for medical purposes.
 Concern over shortages in 99mTc and the disadvantages of the current nuclear reactor route of production have led to renewed interest in the cyclotron production of this medical radioisotope. The starting material for this route is 98% pure 100Mo which must be separated from all its other isotopes and be enriched to the desired purity. The ASP technology of Klydon is well suited for this purpose.
Underneath is a Schematic Comparison of the Nuclear and the Cyclotron Route for the Production of 99mTc
a) nuclear route with fission of 235U which forms through beta-radiation 99mTc.
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Some of the concerns of the nuclear route to produce Mo-100 are:
- Requires enriched uranium as fuel.
- Low conversion efficiencies, compounded by decay during transport.
- Large amounts of radio-active waste with disposal costs that need to be added.
- Difficulties in transporting radio-active molybdenum.
b) ASP technology to isolate 100Mo which is converted in the cyclotron to 99mTc.
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Some of the advantages of the ASP/cyclotron route to manufacture Tc-99 are:
- A stable Mo-100 isotope is produced which is not radioactive and can easily be transported all over the world.
- Low capital requirement for molybdenum isotope production plant.
- Low production cost of Tc-99m compared to the conventional nuclear route.
- Small economic size Mo-100 plant (minimum economically viable size plant is 5kg), thereby reducing investment risk.
- Negligible radioactive waste.
- The lower production cost and the removal of supply constraints will open up undeveloped markets.
- Mo-100 can be stockpiled reducing the risk of supply shortages.
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