Prognostic Utility of 90Y Radioembolization Dosimetry Based on Fusion 99mTc-Macroaggregated Albumin–99mTc-Sulfur Colloid SPECT

Planning hepatic 90Y radioembolization activity requires balancing toxicity with efficacy. We developed a dual-tracer SPECT fusion imaging protocol that merges data on radioactivity distribution with physiologic liver mapping. Methods: Twenty-five patients with colorectal carcinoma and bilobar liver metastases received whole-liver radioembolization with resin microspheres prescribed as per convention (mean administered activity, 1.69 GBq). As part of standard treatment planning, all patients underwent SPECT imaging after intraarterial injection of 37 MBq of 99mTc-macroaggregated albumin (99mTc-MAA) to simulate subsequent 90Y distribution. Immediately afterward, patients received 185 MBq of labeled sulfur colloid (99mTc-SC) intravenously as a biomarker for normal hepatic reticuloendothelial function and SPECT was repeated. The SPECT images were coregistered and fused. A region-based method was used to predict the 90Y radiation absorbed dose to functional liver tissue (DFL) by calculation of 99mTc-MAA activity in regions with 99mTc-SC uptake. Similarly, the absorbed dose to tumor (DT) was predicted by calculation of 99mTc-MAA activity in voxels without 99mTc-SC uptake. Laboratory data and radiographic response were measured for 3 mo, and the survival of patients was recorded. SPECT-based DT and DFL were correlated with parameters of toxicity and efficacy. Results: Toxicity, as measured by increase in serum liver enzymes, correlated significantly with SPECT-based calculation of DFL at all time points (P < 0.05) (mean DFL, 27.9 Gy). Broad biochemical toxicity (>50% increase in all liver enzymes) occurred at a DFL of 24.5 Gy and above. In addition, in uni- and multivariate analysis, SPECT-based calculation of DT (mean DT, 44.2 Gy) correlated with radiographic response (P < 0.001), decrease in serum carcinoembryonic antigen (P < 0.05), and overall survival (P < 0.01). The cutoff value of DT for prediction of 1-y survival was 55 Gy (area under the receiver-operating-characteristic curve = 0.86; P < 0.01). Patients who received a DT of more than 55 Gy had a median survival of 32.8 mo, compared with 7.2 mo in patients who received less (P < 0.05). Conclusion: Dual-tracer 99mTc-MAA–99mTc-SC fusion SPECT offers a physiology-based imaging tool with significant prognostic power that may lead to improved personalized activity planning.