Predictive Dosimetry and Outcomes of Hepatocellular Carcinoma Treated by Yttrium-90 Resin Microsphere Radioembolization: A Retrospective Analysis Using Technetium-99m Macroaggregated Albumin SPECT/CT and Planning Software.

Purpose: To characterize estimated mean absorbed tumor dose (AD), objective response (OR), and estimated target dose of hepatocellular carcinoma (HCC) after resin microsphere yttrium-90 (Y) radioembolization using partition dosimetry.

Materials And Methods: In this retrospective, single-center study, multicompartment dosimetry of index tumors receiving Y radioembolization between October 2015 and June 2022 was performed using a commercial software package and pretreatment technetium-99m macroaggregated albumin single photon emission computed tomography (SPECT)/computed tomography (CT). In total, 101 patients with HCC underwent 102 treatments of 127 index tumors. Patients underwent imaging every 2-3 months after 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 nonresponse (NR). A Cox proportional hazards model evaluated the probability of tumor OR and progression-free survival using AD.

Results: The median follow-up period was 148 days (interquartile range [IQR], 92-273 days). The median AD of OR was 141.9 Gy (IQR, 89.4-215.8 Gy) compared with the median AD of NR treatments of 70.8 Gy (IQR, 42.0-135.3 Gy; P < .001). Only AD was predictive of response (hazard ratio = 2.79 [95% confidence interval {CI}: 1.44-5.40]; P = .003). At 6 months, an AD of 157 Gy predicted 90.0% (95% CI: 41.3%-98.3%) probability of OR. At 1 year, an AD of 157 Gy predicted 91.6% (95% CI: 78.3%-100%) probability of progression-free survival. Partition modeling and delivered activity were predictive of progression (P = .021 and P = .003, respectively).

Conclusions: For HCC treated with resin microspheres, tumors receiving higher AD exhibited higher rates of OR. An AD of 157 Gy predicted 90.0% OR at 6 months.