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[Abstract]

Y PET/CT can be acquired after Y-microsphere selective radiation internal therapy (SIRT) to describe radioactivity distribution. We performed dosimetry using Y-microsphere PET/CT data to evaluate treatment efficacy and appropriateness of activity planning from Tc-MAA scan and SPECT/CT.Twenty-three patients with liver malignancy were included in the study. Tc-MAA was injected during planning angiography and whole body Tc-MAA scan and liver SPECT/CT were acquired. After SIRT using Y-resin microsphere, Y-microsphere PET/CT was acquired. A partition model (PM) using 4 compartments (tumor, intarget normal liver, out-target normal liver, and lung) was adopted, and absorbed dose to each compartment was calculated based on measurements from Tc-MAA SPECT/CT and Y-microsphere PET/CT, respectively, to be compared with each other. Progression-free survival (PFS) was evaluated in terms of tumor absorbed doses calculated by Tc-MAA SPECT/CT and Y-microsphere PET/CT results.Lung shunt fraction was overestimated on Tc-MAA scan compared with Y-microsphere PET/CT (0.060 ± 0.037 vs. 0.018 ± 0.026, P < 0.01). Tumor absorbed dose exhibited a close correlation between the results from Tc-MAA SPECT/CT and Y-microsphere PET/CT (r = 0.64, P < 0.01), although the result from Tc-MAA SPECT/CT was significantly lower than that from Y-microsphere PET/CT (135.4 ± 64.2 Gy vs. 185.0 ± 87.8 Gy, P < 0.01). Absorbed dose to in-target normal liver was overestimated on Tc-MAA SPECT/CT compared with PET/CT (62.6 ± 38.2 Gy vs. 45.2 ± 32.0 Gy, P = 0.02). Absorbed dose to out-target normal liver did not differ between Tc-MAA SPECT/CT and Y-microsphere PET/CT (P = 0.49). Patients with tumor absorbed dose >200 Gy on Y-microsphere PET/CT had longer PFS than those with tumor absorbed dose ≤200 Gy (286 ± 56 days vs. 92 ± 20 days, P = 0.046). Tumor absorbed dose calculated by Tc-MAA SPECT/CT was not a significant predictor for PFS.Activity planning based on Tc-MAA scan and SPECT/CT can be effectively used as a conservative method. Post-SIRT dosimetry based on Y-microsphere PET/CT is an effective method to predict treatment efficacy. 

[Author information]

Song YS1, Paeng JC, Kim HC, Chung JW, Cheon GJ, Chung JK, Lee DS, Kang KW.

1 From the Department of Nuclear Medicine, Seoul National University Hospital (YSS, JCP, GJC, J-KC, DSL, KWK); Department of Nuclear Medicine, Seoul National University Bundang Hospital (YSS); and Department of Radiology, Seoul National University Hospital, Seoul, Korea (H-CK, JWC).