Predictive Dosimetry and Outcomes of Hepatocellular Carcinoma Treated by Y90 Resin Microsphere Radioembolization: A Retrospective Analysis Using 99mTC-MAA SPECT/CT and Planning Software.

PURPOSE: To characterize estimated tumor absorbed dose (ADT ), objective response (OR), and estimated target dose of hepatocellular carcinoma (HCC) following resin microsphere Yttrium-90 (Y90) radioembolization utilizing partition dosimetry.

MATERIALS AND METHODS: In this retrospective, single-center study, multicompartment dosimetry of index tumors receiving Y90 radioembolization between October 2015-June 2022 was performed using MIM SurePlan and pre-treatment technetium-99m macroaggregated albumin SPECT/CT. One hundred and one HCC patients underwent 102 treatments of 127 index tumors. Patients were imaged every 2-3 months post-treatment to determine best response per modified Response Evaluation Criteria in Solid Tumors (mRECIST). Best response was defined as the greatest response category per mRECIST and categorized as OR or non-response (NR). A Cox Proportional Hazards model evaluated the probability of tumor OR and progression free survival using ADT .

RESULTS: Follow-up was a median of 148 (interquartile range [IQR]: 92-273) days. The median ADT of OR was 141.9 (IQR: 89.4-215.8) Gy compared to the median ADT of NR treatments of 70.8 (IQR: 42.0-135.3) Gy (P<0.001). Only ADT was predictive of response (Hazard ratio=2.79 [95% confidence interval (CI): 1.44, 5.40], P=0.003). At 6 months, an ADT of 157 Gy predicted 90.0% (95% CI: 41.3-98.3%) probability of OR. At 1 year, an ADT of 157 Gy predicted a 91.6% (95% CI: 78.3-100%) probability of progression free survival. Partition modeling and delivered activity were predictive of progression (p=0.021, p=0.003).

CONCLUSION: For HCC treated with resin microspheres, tumors receiving higher ADT exhibit higher rates of objective response. An ADT of 157 Gy predicted 90.0% objective response at 6 months.