New Process Improves Production of Short-Lived Scandium Radioisotopes

Researchers at the University of Wisconsin, Madison have developed a new process to make and irradiate accelerator targets for scandium radioisotopes, which can be hard to produce in quantities and purities. Their work was published in Frontiers in Chemistry.

Scandium radioisotopes are potentially useful for medical imaging such as positron emission tomography (PET) scans. However, health care providers do not currently use these isotopes to image cancer because they are difficult to produce in the amounts and purities appropriate for human use. In particular, they must be made using special isotopically enriched calcium targets. These targets are rare, expensive, and difficult to use in an accelerator.

Scandium-43 and scandium-44 are two of the most promising options for theranostic medicine paired with therapeutic scandium-47. Making these  isotopes  requires costly titanium and calcium starting materials. They also require difficult irradiation and chemical processing to isolate. These factors have inhibited the development of scandium-based treatments and limited their availability.

With funding from the US Department of Energy Isotope Program, the researchers studied five nuclear reactions that form scandium-43 and scandium-44 from proton and deuteron irradiation of calcium oxide  accelerator  targets. The experiments looked at the quantities and purities of scandium-43 and scandium-44 made when starting with commercially available targets with calcium enriched in the isotopes calcium-42, calcium-43, and calcium-44. The largest yields and highest purities measured were of scandium-44 when calcium-44 was irradiated with protons; this made 120 millicuries in an hour of irradiation with more than 99.7%purity. The researchers also developed processes to chemically purify scandium and to recover the very expensive calcium target materials, which helps make them sustainable in a modern hospital environment.

The scandium-43 and scandium-44 radioisotopes produced from all reactions studied are pure enough to use as radioactive drugs that target cancer. In modern diagnostic medical procedures using PET scanners, the resolution and quantitative performance of these scandium radioisotopes is superior to the existing clinical standard of care radiometal isotope gallium-68.