Purpose: To identify clinical factors and tumor characteristics that affect the relative uptake of yttrium-90 (Y90) microparticles within hepatocellular carcinoma (HCC) in relation to surrounding perfused normal liver tissue.
Materials and Methods: A retrospective review was conducted involving all patients who underwent pre-Y90 radioembolization planning with 99mTc-MAA hepatic artery embolization at a single institution from 2016 to 2020. Utilizing commercial software for individual dose planning (Simplicit90Y, Mirada Medical), pre-procedural MRI examinations were co-registered to 99mTc-MAA SPECT-CT images. The borders of the tumor as well as surrounding perfused normal liver were manually drawn. From these tumor and liver volumes, dimensionless image “counts” originating from each of these volumes were calculated automatically by the dose planning software. Normalized ratio of counts originating from tumor to surrounding perfused normal liver were calculated for each case (T:N ratio). T:N ratio differences related to etiology of cirrhosis, tumor size, multiplicity of tumors, prior intra-arterial therapy, prior ablation therapy, as well as other clinical factors and tumor structural features were compared using Student’s t-test, ANOVA, and linear regression.
Results: Prior ablation therapy (p=.0001) and multifocal HCC (p=.03) were found to be associated with an increased T:N ratio, while larger sized singular HCC (p=.03) were associated with lower T:N ratios. Etiology of patient cirrhosis (p=.98), Childs Pugh score (p=.47), and other patient factors were found to have no significant T:N ratio association.
Conclusion: An underlying assumption of partition model dosimetry is a uniform T:N ratio of Y90 invariant to the clinical scenario. Our data suggests that smaller sized HCC, cases of multifocal HCC, and HCC which have been previously treated with ablation therapy preferentially uptake a higher relative quantity of 99mTc-MAA compared to surrounding normal liver as compared to larger, singular HCCs which have not been previously treated. These findings suggest certain types of HCC in certain patients may be successfully treated with lower doses of intraarterial Y90 to achieve similar intratumoral Y90 uptake.