Compact cyclotrons for the production of tracers and radiopharmaceuticals

Positron Emission Tomography (PET) is a method for determining biochemical and physiological processes in vivo in a quantitative manner. The most commonly used radionuclides are C-11, N-13, O-15 and F-18, with respective half-lives of approximately 20 min, 10 min, 2 min, and 110 min. F-18 labeled FDG (fluoro-2-deoxy-D-glucose) is now the most frequently used radiopharmaceutical and finds its application prominently in the field of oncology. Originally, the production of these radionuclides was performed with the existing accelerators, designed for nuclear physics, but with increasing interest in the PET methodology specially designed PET-production cyclotrons became available. The nuclear reactions involved are (p,n), (d,n), (p,alpha) and (d,alpha) and the thresholds for the nuclear reactions involved are 5 to 6 MeV. Based on these values and on other parameters, a proton 15 to 20 MeV cyclotron is often chosen. Since the half-life of a radionuclide limits the production time, the maximum beam current is an important parameter, together with the target construction, for the ultimate yield obtainable. In the development of special PET production cyclotrons, attention has also been paid to improve the extraction efficiency and the possibility of multiple extractions by designing negative ion cyclotrons. Commercial cyclotrons can often be acquired as an easy to operate integrated radionuclide production unit including targetry and some units. Regional FDG factories are nowadays being created to fulfil the demand for PET radiopharmaceutics. The possible choices in commercially available cyclotrons for the production of PET radionuclides will be discussed.