Utility of SPECT/CT Imaging in Y-90 Microsphere Therapy

Objectives Demonstrate the utility of SPECT/CT, along with planar data, in Y-90 microsphere pre-therapy and post-therapy procedures.

Methods Intra-arterial radioembolization with Y-90 labeled microspheres is used to treat nonresectable liver tumors. At Mayo Clinic in Arizona, pre-Tx liver planar mapping and SPECT/CT imaging is conducted using Tc99m MAA to evaluate extrahepatic particle deposition and shunting of tracer to the lungs. Both planar and Bremsstrahlung SPECT/CT imaging are conducted following the Y-90 administration. The SPECT/CT data sets are visually compared and reported on with a focus Y-90 distribution versus the MAA mapping.

Results All planar and SPECT/CT imaging are conducted immediately following administration in IR. SPECT/CT images provide a more comprehensive means of visualizing Y-90 activity outside of the liver than planar imaging alone, and thus serve as a better predictor of post-Tx complications such as extra-hepatic tissue necrosis, which can lead to bleeding and ulceration. Two specific examples have reinforced the importance of SPECT/CT. In one patient, intra-abdominal MAA deposition on the therapy planning scan led to the cancellation of the treatment due to the concern for complications. This was not visualized on the planar images. In the second case, Bremsstrahlung SPECT/CT data confirmed the appropriate deposition of the microspheres and negated extra-hepatic placement as the cause for the patient’s post-procedure discomfort.

Conclusions Challenges do exist with SPECT/CT Bremsstrahlung imaging. Low photon yield, scatter and blurring from lack of point spread function reconstruction algorithm do limit the quality of data acquired. Due to these limitations, PET Y-90 imaging is superior, when available. Institutions that lack onsite PET facilities should not overlook Y-90 SPECT/CT imaging. SPECT/CT and planar images should be acquired on all Y-90 microsphere therapy patients. Benefits to both patient and IR radiologists have been noted. Radiologists in IR commonly refer to the SPECT/CT data sets to confirm and refine their technique to better manage patients and improve patient care.