Theranostic Imaging of Yttrium-90

Figure 1

Yttrium-90 as a theranostic agent (i.e., it demonstrates both therapeutic and diagnostic attributes). Yttrium-90 (⁹⁰Y, center) is a high-energy β⁻ emitting radioisotope used clinically for targeted radiotherapy (upper left). The targeted radiotherapy applications include direct injection of ⁹⁰Y into a body space or cavity, conjugation of ⁹⁰Y to a peptide for peptide receptor radionuclide therapy (PRRT), or an antibody for radioimmunotherapy (RIT), or incorporation of ⁹⁰Y into a resin or glass microsphere for radioembolization (RE) therapy. The high-energy β⁻ particle emission produces a continuous spectrum bremsstrahlung radiation which can then be imaged using conventional nuclear medicine imaging systems such as planar gamma cameras, SPECT, and SPECT/CT (lower left). Although the vast majority of ⁹⁰Y decays are β⁻ emitting, 32 per million ⁹⁰Y decays result in internal pair production that can be readily imaged using conventional PET/CT and PET/MRI systems (lower right). The high-energy β⁻ particle emission also produces continuous spectrum light photons or Cerenkov luminescence which can then be imaged using existing bioluminescence imaging systems (upper right). These 3 noninvasive imaging approaches allow for simultaneous diagnostic assessment/localization of the therapeutic ⁹⁰Y radioactivity.