Semi-Quantitative Analysis of Post-Transarterial Radioembolization Y-90 Microsphere Positron Emission Tomography Combined with Computed Tomography (PET/CT) Images in Advanced Liver Malignancy: Comparison With Tc-99m Macroaggregated Albumin (MAA) Single Photon Emission Computed Tomography (SPECT)

Abstract

Objectives The purpose of this study is to evaluate the correlation between pretreatment planning technetium-99m (Tc-99m) macroaggregated albumin (MAA) SPECT images and posttreatment transarterial radioembolization (TARE) yttirum-90 (Y-90) PET/CT images by comparing the ratios of tumor-to-normal liver counts. Methods Fifty-two patients with advanced hepatic malignancy who underwent Y-90 microsphere radioembolization from January 2010 to December 2012 were retrospectively reviewed. Patients had undergone Tc-99m MAA intraarterial injection SPECT for a pretreatment evaluation of microsphere distribution and therapy planning. After the administration of Y-90 microspheres, the patients underwent posttreatment Y-90 PET/CT within 24 h. For semiquantitative analysis, the tumor-to-normal uptake ratios in Y-90 PET/CT (TNR-yp) and Tc-99m MAA SPECT (TNR-ms) as well as the tumor volumes measured in angiographic CT were obtained and analyzed. The relationship of TNR-yp and TNR-ms was evaluated by Spearman's rank correlation and Wilcoxon's matched pairs test. Results In a total of 79 lesions of 52 patients, the distribution of microspheres was well demonstrated in both the SPECT and PET/CT images. A good correlation was observed of between TNR-ms and TNR-yp (rho value=0.648, p<0.001). The TNR-yp (median 2.78, interquartile range 2.43) tend to show significantly higher values than TNR-ms (median 2.49, interquartile range of 1.55) (p=0.012). The TNR-yp showed weak correlation with tumor volume (rho=0.230, p=0.041). Conclusions The Tc-99m MAA SPECT showed a good correlation with Y-90 PET/CT in TNR values, suggesting that Tc-99m MAA can be used as an adequate pretreatment evaluation method. However, the Tc-99m MAA SPECT image consistently shows lower TNR values compared to Y-90 PET/CT, which means the possibility of underestimation of tumorous uptake in the partition dosimetry model using Tc-99m MAA SPECT. Considering that Tc-99m MAA is the only clinically available surrogate marker for distribution of microsphere, we recommend measurement of tumorous uptake using Y-90 PET/CT should be included routinely in the posttherapeutic evaluation.