Tc-99m MAA Mapping Prior to Y-90 Liver Radioembolization; Factors that mayaffect Pulmonary Shunt Fraction

Purpose: To evaluate differences in shunt fraction and possible factors contributing to these differences in patients undergoing Tc-99m macroaggregated albumin (MAA) mapping prior to selective internal radiation therapy (SIRT) with Y-90 microspheres. Materials and methods: Retrospective analysis was performed on data from 130 patients with hepatocellular carcinoma (HCC) or liver metastases, who underwent Y-90 radioembolization over a 6-year period. All patients who received treatment had undergone Tc-99m MAA mapping. Overall 141 Tc-99m MAA injections and 199 Y-90 treatments were performed. Three patients did not qualify for Y-90 treatment following Tc-99m MAA mapping due to high pulmonary shunt fraction. We compared pulmonary shunt fraction between patients with HCC and those with metastatic liver disease and between patients who had mapping of the entire liver, versus selective mapping of the affected segment. Three types of statistical analysis tests were performed: Kolmogorov-Smirnov (KS), Mann- Whitney (MW) and Fligner-Killeen (FK) tests. Results: Although HCC and non-HCC groups had similar distribution of shunt fractions qualitatively, relatively large shunt fractions were slightly more common in HCC group. In diffuse injections, most of the shunt fractions were concentrated between 0 and 5%, but with a long tail to the right. In more selective injections, most were concentrated between 0 and 10%. There was a trend for overall higher median shunt fraction in the diffuse mapping group compared with the selective mapping group, however this was only statistically significant in the HCC patients subset (median shunt of 3.2% in diffuse vs. 6.1% in selective group; p=0.001). Conclusions: Shunt fraction is overall higher in HCC, likely due to underlying cirrhosis as well as intratumoral arteriovenous shunting. Shunt fraction also tends to be higher when the affected liver is selectively injected compared with when the entire liver is being mapped.