Changes over the years in radiopharmaceutical design.

Of the many uses of radiopharmaceuticals, developing radiotracers that contribute significantly to diagnosis and therapy of patients has been a major focus. This requires a broad spectrum of expertise including that of the attending physician who lends insight to an unmet clinical need neither addressed by other imaging techniques nor by analysis of tissue, blood, and urine for diagnostics and addressed by pharmaceuticals for therapeutic applications. The design criteria have depended on radiochemistry, on matching the radiopharmaceutical with the imaging devices, and basing the design on current pharmaceuticals. The chelates of technetium-99m were based on radiochemistry rather than clinical need yet are still used today in >70% of the clinical studies. Targeted radiotracers in neurologic and psychiatric disorders, inflammation, cardiovascular disease, and oncology have all been studied with the goal of determining the change in the density of a target protein as a function of disease or treatment or, especially in oncology, detection of the total extent of disease. In the latter approach, PET in university settings leads the way; however, the use of SPECT/CT has increased the specificity of SPECT imaging to complement the cost-effective generator and instant kits already available. Remarkable advances have been achieved in radionuclide therapy using theragnostic agents, with the exclusive domain of oncology. For this application the design of radionuclide therapy follows that used for diagnostics. The increased impact of the discipline depends on the opportunity to continue the search for the most appropriate radiopharmaceutical for each individual patient.