Molybdenum-99 / technetium-99m as the most important radioisotope in diagnostics

One of the most commonly used isotopes is Technetium (Tc-99m), the daughter isotope of Molybdenum-99 (Mo-99). The radioisotope Tc-99m is used in up to 80% of applications of in-vivo diagnostics. This corresponds to more than 30 million tests worldwide each year. In Germany alone, about 60,000 tests a week are performed using Tc-99m. This corresponds to about one-tenth of the world's demand for Tc-99m. It is used mainly for the investigation of thyroid function, but also for the diagnosis of diseases of other organs such as the lungs, heart, liver, gall bladder and the skeleton. 

Mo-99 production by irradiation

The most efficient and widely used method for the production of Mo-99 / Tc-99m is nuclear fission. The manufacture of Tc-99m involves the fission of U-235 to the fission product Mo-99, which decays to Tc-99m with a half-life of 66 hours. Tc-99m itself decays with a half-life of 6 hours to Tc-99 while emitting low energy gamma radiation. The half-life is the time in which half of the radioactive material decays. Since both Mo-99 with 66 hours and Tc-99m with 6 hours have short half-lives, it is immediately clear that the most widely used radioisotope in medicine, Tc-99m, cannot be stored. Therefore, the various steps in the production chain must proceed swiftly and be well-coordinated in order to supply hospitals with the necessary amount of Tc-99m at the right time.

Molybdän-99 supply chain (Image: FRM II/TUM)

After irradiation of the U-235 targets (Al-coated plates or tubes), they are subsequently chemically dissolved in a specially equipped device (processor) where the Mo-99 bound in the target is separated. For use in hospitals, the Mo-99 comes in so-called Mo-99 / Tc-99m generators where the Mo-99 decays to Tc-99m, which is then eluted or "milked" on-site at the hospital. Depending on the application, the Tc-99m can then be attached to a suitable "smart" carrier molecule, which later recognizes, for example, tumour cells in a patient and docks with them. The patient is injected with Tc-99m with or without a pharmaceutical label. In decaying toTc-99,Tc-99m emits γ-radiation, which is then measured depending on the location. The short lifetime of 6 hours of the diagnostic or therapeutic isotope Tc-99m and the low energy of the γ-rays minimize the exposure of the patient to radiation.

Significant contribution of the FRM II to security of supply Mo-99 / Tc-99m

Due to the transient nature of the initial isotope Mo-99 and the high demand for Mo-99 / Tc-99m, Europe – and also Germany as the largest single consumer – requires its own medium and long term secured supply chain for Mo-99 / Tc-99m. With the completion of the Mo-99 irradiation facility currently under construction, the FRM II will significantly contribute to the supply security of Mo-99 / Tc-99m in Germany and Europe.

Global efforts to ensure the supply of Mo-99 / Tc-99m

Worldwide, the current and future operators of irradiation facilities for the production of Mo-99, as well as representatives of all partners in industry involved in the production chain, are working together in a group set up by the OECD / NEA, the so-called HLG-MR (High-level Group on the Security of Supply of Medical Radioisotopes), to ensure the sustainable delivery of the radioisotope Mo-99 / Tc-99m in future years. The results of this group are regularly published by the OECD / NEA on their websites.

Refereces:

1The Supply of Medical Radioisotopes: The Path to Reliability, ISBN-978-92-64-99164-4, OECD 2011

2Radionuklidengpass: Ursachen und Lehren, A. Bockisch, F. Gründwald, J. Kotzerke; Nuklearmedizin 2009; 48:55-57