Partition Dosimetry and Outcomes of Metastatic Neuroendocrine Tumors Following Yttrium-90 Resin Microsphere Radioembolization

To characterize estimated average tumor absorbed dose (ADT) and objective response neuroendocrine tumor (NET) following resin microspheres Yttrium-90 (Y90) radioembolization utilizing partition dosimetry.In this retrospective, single-center study, multicompartment dosimetry of index tumors receiving Y90 radioembolization between 2013-2022 used MIM SurePlan and technetium-99m macroaggregated albumin single-photon emission computed tomography combined with computed tomography. Thirty-six NET patients underwent treatment of 56 index tumors. Median patient age was 62 (interquartile range [IQR]: 56-70) years, 23/36 (64%) were female, and Eastern Cooperative Oncology Group status were 0 (26/36, 72%), 1 (6/36, 17%), and 2 (1/36, 3%). Patients were imaged every 3-6 months post-treatment to determine best response per Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 and modified RECIST (mRECIST) criteria. Best response was defined as greatest response category. Responses were categorized objective response (OR) or non-response (NR). Wilcoxon rank-sum test evaluated differences in continuous, and Pearson's Chi-squared test evaluated differences in categorical variables.Median follow-up was 582 (IQR: 187-1227) days. Per RECIST 1.1, 27/36 (75%) patients had OR vs 9/36 (25%) NR. Thirty-three of 36 (92%) patients had hypervascular, mRECIST-evaluable tumors. Among them, 28/33 (85%) patients had mRECIST OR vs 5/33 (15%) NR. The mRECIST OR group received a higher ADT than NR (median 107 [IQR: 95.1-154] vs. 70.4 [IQR: 62.9-87.6] Gy, P=0.048). All tumors receiving at least 120 Gy experienced mRECIST OR.In hypervascular NET, higher tumor dose improved tumor response per mRECIST. Doses > 120 Gy led to objective response with Y90 resin microspheres.