Purpose: To evaluate the accuracy of scout dose yttrium-90 (Y90) resin microspheres vs. technetium-99m MAA (Tc99m-MAA) in predicting the therapeutic dose Y90 liver biodistribution for radioembolization (RE) planning in hepatocellular carcinoma (HCC) patients.
Materials and Methods: In a prospective single-arm clinical trial patients with HCC undergoing Y90 RE were recruited. Inclusion criteria included unilobar disease with ≤3 lesions with the largest lesion < 7cm. Each patient underwent mapping angiography study with Tc99m-MAA and MAA SPECT/CT followed by second mapping study using 15 mCi Y90 resin microspheres and Y90 SPECT/CT and PET/CT. Prospective treatment planning with MAA data was performed using partition model with the goal of >200 Gy to the targeted tumor. Prescribed Y90 activity minus previously administered scout activity was administered 3 days after the mapping studies. Same microcatheter type and position were used for all stages of the study in each patient. Sureplan®(MIM Software, Cleveland, OH) was used for all dosimetry analyses. Using paired t-test, the tumor:normal (TNR) calculated by MAA SPECT and scout dose Y90 SPECT and PET were compared to that of therapeutic dose Y90 SPECT and PET.
Results: First N=15 patients treated in the clinical trial are included in this interim analysis. Mean TNR by MAA SPECT was 2.33. Mean TNR by scout dose Y90 SPECT and PET were 1.79 and 2.59 respectively. Mean TNR by therapeutic dose Y90 SPECT and PET were 1.75 and 2.65 respectively. MAA TNR was greater than both Y90 scout and therapeutic dose TNR’s calculated by SPECT (p’s< 0.001). MAA TNR was statistically similar to both scout dose and therapeutic dose Y90 TNR’s calculated by PET (p=0.33 and p=0.55 respectively). Y90 Scout and therapeutic dose TNR’s calculated by SPECT were similar (p=0.59) and the same finding was observed for Y90 TNR’s calculated by Y90 scout and therapeutic dose PET (p=0.74).
Conclusion: Y90 scout dose is an accurate predictor of therapeutic Y90 dose biodistribution in the liver on both SPECT and PET respectively. On the other hand, Tc99-MAA TNR was significantly greater than both Y90 scout and therapeutic dose TNR’s on SPECT, whereas it was statistically similar to that of PET.