Dosimetry of Y-90 Microspheres Utilizing Tc-99m SPECT and Y-90 PET

Dosimetry for yttrium-90 radioembolization continues to generate interest and controversy, as multiple approaches have been used effectively. Traditionally, simple formulas primarily based on patients' body weight or perfused liver volume were used. Over the past several years, dosimetry refinements have led to marked improvements in this therapy from both a safety and efficacy standpoint. Technetium-99m macroaggregated albumin single photon emission computed tomography (SPECT) optimizes pretreatment dosimetry to ensure delivery of a therapeutic radiation dose to the tumor while minimizing nontarget radiation to healthy hepatic tissue. Post-treatment yttrium-90 PET utilizing the inherent internal pair production of yttrium-90 accurately calculates the absorbed dose to tumors and to the normal hepatic parenchyma, which correlates with patient outcomes. As dosimetric calculations become more complex, quantitative imaging with Tc-99m SPECT and Y-90 PET may set the new standard for radioembolization dosimetry.