Predictive value of ^99mTc-MAA SPECT for ⁹⁰Y-labeled resin microsphere distribution in radioembolization of primary and secondary hepatic tumors

This study analyzed the predictive value of ^99mTc-labeled macroaggre-gated albumin (^99mTc-MAA) SPECT for ⁹⁰Y-labeled resin microsphere therapy (radioembolization) by comparing uptake on pretherapeutic ^99mTc-MAA SPECT with uptake on posttherapeutic ⁹⁰Y-bremsstrahlung SPECT. Methods: We included 502 patients (55% male; mean age ± SD, 62 ± 11 y) who underwent radioembolization between 2005 and 2013 because of primary or secondary liver malignancies (colorectal cancer [n = 195, 38.8%], neuroendocrine tumors [n = 77, 15.3%], breast cancer [n = 68, 13.5%], hepatocellular carcinoma [n = 59, 11.8%], cholangiocellular carcinoma [n = 40, 8.0%], or urologic tumors [n = 14, 2.8%]). Manually drawn regions of interest around tumors and adjacent healthy liver tissue for up to 3 lesions per patient on ^99mTc-MAA and ⁹⁰Y-bremsstrahlung scans were used to quantify mean counts per pixel and evaluate the mean tumor-to-background ratio (TBR). Data were given as mean ± SD. Additionally, uptake in lesions on ^99mTc-MAA and ⁹⁰Y-bremsstrahlung scans was graded visually as homogeneously higher than (grade 1), heterogeneously higher than (grade 2), equal to (grade 3), or lower than (grade 4) uptake in normal liver tissue. The Mann-Whitney U test and Spearman correlation were used to evaluate statistically significant differences between ^99mTc-MAA and ⁹⁰Y-bremsstrahlung SPECT. Results: In total, 1,008 lesions were analyzed. Of the 23% (230/1,008) of lesions that had grade 1 uptake on ^99mTc-MAA SPECT, 81% (186/230) remained grade 1 after radioembolization whereas 16% (37/230) were grade 2. Of the lesions with grade 2 uptake on ^99mTc-MAA SPECT, 16% had grade 1 uptake and 82% grade 2 uptake after radioembolization. Of the lesions with grade 3 uptake, however, 27% had grade 1 uptake and 47% grade 2 uptake after radioembolization. Even among the lesions with grade 4 uptake on ^99mTc-MAA SPECT, 21% had grade 1 uptake and 46% grade 2 uptake after radioembolization. The mean TBR on ^99mTc-MAA and ⁹⁰Y-bremsstrahlung SPECT showed a significant, though low, correlation in the total population (r = 0.26; P < 0.001) and in hepatocellular carcinoma (r = 0.4; P < 0.001), cholangiocellular carcinoma (r = 0.3; P < 0.05), breast cancer (r = 0.3; P < 0.001), colorectal cancer (r = 0.2; P < 0.001), and neuroendocrine tumors (r = 0.2; P < 0.01). Conclusion: Although significant for most lesions, the correlation between ^99mTc-MAA and ⁹⁰Y-microsphere mean TBR was low. Classifying uptake into 4 grades revealed that lesions with high uptake on ^99mTc-MAA SPECT maintain high uptake within radioembolization. More than 60% of lesions with a pretherapeutically lower uptake than in healthy liver tissue, however, showed high uptake within radioembolization. Patients with low tumor uptake on pretherapeutic ^99mTc-MAA imaging should not be excluded from radioembolization.