Concordant F-18 FDG PET and Y-90 Bremsstrahlung scans depict selective delivery of Y-90-microspheres to liver tumors: confirmation with histopathology.

Selective Internal Radiation Therapy using yttrium-90 (Y-90) microspheres is a novel method for the treatment of advanced liver cancer. The procedure involves intrahepatic arterial delivery of the Y-90 microspheres. Since hepatic tumors derive their blood supply mainly from the hepatic arteries, it is assumed that the microspheres will be preferentially delivered to tumor cells. However, this has not been confirmed at histology. We report a case of hepatic metastasis from an unknown primary, where treatment with Y-90 microspheres was the only available option due to inoperability and low tolerance to chemotherapy. Pretherapy F-18 FDG-PET scan defined the distribution of the active tumor within the liver. Following the injection of Y-90 microspheres, Bremsstrahlung imaging showed uptake only in the F-18 FDG-PET-defined tumor area. Post therapy debulking surgery was performed and histopathology of tumor samples confirmed the preferential distribution of the injected microspheres in the hepatic tumor circulation with very little in the healthy liver tissue. The case confirms the preferential blood flow to hepatic tumors as depicted by the distribution of Y-90 microspheres injected directly in the hepatic arteries. It also demonstrates that concordance between F-18 FDG-PET and Y-90 Bremsstrahlung scans can be a useful clue to the in vivo distribution of microspheres.