03:45 PM Abstract No. 117 Quantitative baseline imaging biomarkers for Yttrium-90 distribution on bremsstrahlung SPECT and tumor response prediction after radioembolization

To identify baseline imaging features in patients with liver cancer that best correlate with Yttrium-90 (90Y) distribution on immediate post-procedural single photon emission computed tomography (SPECT) and predict tumor response to radioembolization (RE). This retrospective study included 38 patients with hepatocellular carcinoma (HCC) (n=23) and non-HCC hepatic malignancies (n=15) who underwent 40 resin-based RE treatments. Multi-phasic contrast-enhanced MR or CT imaging was obtained prior to and bremsstrahlung SPECT within two hours after RE. Total (TTV, cm³) and enhancing tumor volume (ETV, cm³, and percent), tumor (TB, percent) and enhancing tumor burden (ETB percent) were volumetrically assessed on baseline imaging. After multimodal image registration of baseline MRI or CT and SPECT/CT, 90Y distribution was quantified on SPECT as tumor-to-normal-liver-ratio (TNR). Up to two dominant lesions per treated lobe were analyzed. Follow-up imaging within 4 months was available for 23 patients with 25 lobar treatments, and was used for response assessment according to the quantitative European Association for the Study of the Liver (qEASL) criteria. Statistical tests included Mann-Whitney-U, Pearson correlation, and linear regression. In HCC patients (18/23 males, mean age 62.39±8.62 years) with 34 dominant lesions, high baseline ETV% significantly correlated with a high TNR on SPECT, demonstrating greater 90Y uptake in the tumor relative to the liver parenchyma (p<0.001). In non-HCC patients (9/15 males, mean age 61.13±11.51 years) with 24 dominant lesions, a correlation between ETV% and TNR was observed as well (p=0.039). With regards to tumor response, the change of ETV% significantly correlated with TNR in HCC (p=0.039) but not in non-HCC patients (p=0.886). Additionally, Child-Pugh class B patients had significantly more 90Y deposition in non-tumorous liver (p=0.021) and had a greater lung shunt fraction (p=0.049) compared to Child-Pugh A patients. This study identified ETV% as a quantifiable imaging biomarker on pre-procedural MRI and CT to predict 90Y distribution on post-RE SPECT. Additionally, this study validated the 90Y dose-response-relationship for HCC treated with RE.