Quantitative Comparison of Yttrium-90 (90Y)-Microspheres and Technetium-99m (99mTc)-Macroaggregated Albumin SPECT Images for Planning 90Y Therapy of Liver Cancer

Yttrium-90 (Y-90)-microspheres administered via the hepatic artery has been used for the treatment of unresectable primary or metastatic cancer in the liver Poor to Y-90 therapy, however, the Y-90 administered activity and the percent shunting to lungs must be determined, most commonly by gamma camera imaging of technetium-99m (Tc-99m)-macroaggregated albumin (MAA) The purpose of the current study was to identify and evaluate an objective measure of the correlation of Y-90 and MAA activity distributions and thus assess the reliability of MAA imaging for evaluation of Y-90 administered activity and tumor and liver radiation doses The MA study consisted of two acquisitions After administration of 185 MBq of MAA, a partial-body or so-called breakthrough scan was performed in order to determine the percent shunting to lungs Immediately after a breakthrough scan, a combined single-photon emission computed tomography (SPECT)/transmission computed tomography (CT) scanner was used to image MAA distribution in order to derived the prescribed Y-90 administered activity based on tumor and liver dosimetry Y-90 SPECT/CT was performed 2-4 weeks later and activities used were in the range of 777-2,442 MBq In order to compare Y-90 and MAA SPECT images, first the respective CT image sets were registered using a transform based on normalized mutual information The transform thus derived was used to align the Y-90 and MAA SPECT image sets, and the Spearman's (rho) rank correlation as well as image distance (L2-norm) between the registered SPECT images were then calculated The Spearman's rank correlation values ranged from 0 451 to 0 818 and the L2 distances from 0 626 to 2 889 Based on visual inspection, the registration of the Y-90 and MAA SPECT images appeared reasonably accurate The regression coefficient (r) between visual scoring and the Spearman's rank correlation was 0 65 and between visual scoring and L2 distance 0 61 The Spearman's rank correlation thus appears to be more reliable than the image distance for assessing the correlation of the Y-90 and MAA images