Abstract No. 262 Tumor-to-Normal Tissue Ratio Preceding Y90 Radioembolization in Hypovascular Liver Tumors Using Multi-Compartment Dosimetry

Hypovascular tumors are particularly difficult to treat effectively with trans-arterial therapies due to low tumor-to-normal liver (T/N) tissue perfusion. This study aims to investigate T/N ratio of patients receiving yttrium-90 (Y90) radioembolization glass microspheres for tumors that are hypovascular on pre-treatment CT or MR. Institutional review board approved this retrospective study of patients who underwent radioembolization with 90Y glass microspheres at a single institution for hypovascular liver tumors between 2022 and 2023. Patients were included if tumors were hypoattenuating relative to normal liver on properly timed arterial phase CT or MRI. Patients were excluded if tumors were necrotic. Immediately following planning angiography with 99mTc-MAA administration, all patients received SPECT/CT scans. Multi-compartment voxel-based dosimetry was performed using Y90 dosimetry software (Simplicit90Y, Boston Scientific Corporation) and T/N ratios were calculated from dosimetry data. The final cohort included 23 patients (10 female, 13 male, median age 69, range 52-85 years) with hypovascular liver tumors that underwent Y90 glass microsphere treatments. Ten patients had cirrhosis of varying etiologies, including HCV (n=4), alcohol (n=5), and non-alcoholic fatty liver disease (n=1). Three of the patients had previously received Y90. Patients had either hepatocellular carcinoma (n=9), intrahepatic cholangiocarcinoma (n=6), or liver metastasis (n=8). All patients were Child-Pugh A, with ECOG status 0 (n=11), 1 (n=11), or 2 (n=1). Treatment strategies included lobar (5/23, 22%), lobar plus segment (3/23, 13%), multiple radiation segmentectomy (7/23, 30%), and single radiation segmentectomy (8/23, 35%). The mean index tumor size was 5.2 ± 3.2 cm. The mean lung shunt fraction was 5.5 ± 3.3% for the patient cohort. Prescribed dose to the perfused volume ranged from 120 to 625 Gy with a mean of 286.4 ± 154.0 Gy. The mean tumor absorbed dose was 425.2 ± 282.5 Gy, and the mean normal liver absorbed dose was 85.4 ± 43.0 Gy. T/N ratios ranged from 0.28 to 4.02, with a mean of 1.61 ± 0.83. T/N ratios calculated using multi-compartment dosimetry were on average greater than 1.00 for the patient cohort analyzed, indicating that hypovascular tumor uptake of Y90 dose may be greater than previously assumed and patients with such tumor morphologies could benefit from proceeding with treatment.