Quantification of Tc-99m macroaggregated albumin liver perfusion as a predictor of tumor response to intra-arterial therapy with yttrium 90 spheres
Authors: Gayed Isis , Tripathee Neroj , Kaur Harleen , Cohen Alan 
Published: November 2021

Objectives:
It remains unclear whether quantifying the pre-therapy tumor Technetium 99m macro aggregated albumin (Tc 99m MAA) localization can accurately predict the response to Yttrium 90 (Y-90) spheres therapy. Present studies are limited and with contradictory results. The aim of this study is to determine if quantification of Tc-99m MAA in hepatic tumor lesion(s) on pretherapy planning nuclear scan can predict the degree of tumor response after radioembolization using Y-90 Spheres.

Material and Methods:
We retrospectively included patients with primary liver cancers or metastases who were treated with SirSpheres or TheraSpheres. All patients had a Tc-99m MAA scan with an average dose of 5.0mCi injected aseptically in either the right, left, or common hepatic artery. The patients were subsequently transferred for imaging using planar and single-photon emission computed tomography (SPECT) of the abdomen and planar images of the chest. We calculated geometric mean of radiotracer counts in the largest lesion in the lobe to be treated by placing same size region of interest (ROI) around the largest lesion on the anterior and posterior planar images. Subsequently, an irregular ROI around the liver or lobe to be treated were drawn to calculate the geometric mean of counts in the liver. The percent tracer accumulation in the largest lesion was calculated by dividing the geometric mean of counts in the largest lesion by the geometric mean of counts in the liver or lobe and multiplying by 100%. The size of this largest lesion was obtained on the most recent CT or magnetic resonance imaging (MRI) in cm in 2 directions prior to treatment with Y-90 Spheres. The extent of the response to Y-90 Spheres therapy was re-evaluated with 3 months follow-up MRI or CT by measuring the decrease in the largest lesion size. Comparison of the percent Tc-99 MAA count accumulation in the largest lesion on the pre-therapy scan with the reduction in size using anatomic imaging was performed.

Results:
A total of 30 patients were included (16 hepatocellular carcinoma, eight colorectal, three breast, one neuroendocrine, one cholangiocarcinoma, and one cervical metastases). There were 14 patients in stable disease or progressive disease group (SD/PD gp) and 16 patients in partial response or complete response group (PR/CR gp). The median lesion size was 3.5 cm in the PD/SD gp versus 2.8 cm in the PR/CR gp (P = 0.31). Additionally, the median delivered Y90 Spheres treatment dose was 51.3 mCi in the PD/SD versus 43.2 mCi in the PR/CR gp (P = 0.22). The percent median largest lesion to liver concentration was 21.9% in the PR/CR gp versus 23.3% in the PR/CR gp (P = 0.74). There was no significant difference in percent Tc-99m MAA distribution in the largest liver lesion between the SD/PD gp and the PR/CR gp.

Conclusion:
The degree of Tc-99m MAA localization in the largest tumor lesion in the liver compared to the remainder of the liver as quantified from planar images does not predict the response to Y-90 spheres therapy.