Tc-MAA SPECT/CT imaging before Y-SIRT for reflecting the distribution of Y resin microspheres in tumors and the liver: a comparison with Y PET/CT verification imaging.

BACKGROUND

Y microsphere selective internal radiation therapy (Y-SIRT) has been widely used for the treatment of unresectable primary or metastatic liver tumors. Tc-macroaggregated albumin single-photon emission computed tomography-computed tomography (Tc-MAA SPECT/CT) and Y positron emission tomography-computed tomography (Y PET/CT) are performed before and after Y-SIRT, respectively, for pretreatment dose distribution assessment and posttreatment verification of microsphere distribution. The purpose of this study was to evaluate the predictive value of Tc-MAA SPECT/CT for dose distribution assessment and analyze its potential impact on the calculation of absorbed dose to normal liver tissue. To achieve this, the differences in tumor imaging, liver tumor-to-normal ratio (TNR), and normal liver tissue absorbed dose (Dliver) between Tc-MAA SPECT/CT and Y PET/CT were analyzed.

METHODS

Thirty-eight patients with primary or metastatic liver cancer who underwent Y-SIRT were retrospectively enrolled. Their Tc-MAA SPECT/CT and Y PET/CT images were analyzed, and the TNR measured by Tc-MAA SPECT/CT (TNR) and Y PET/CT (TNR) was compared. The absolute differences in TRN (ΔTNR) and percent differences in TNR (%TNR) between the two values were also calculated. Correlation analysis was conducted with patient's age, body mass index, total liver volume, and target tumor volume. The absolute differences in D (ΔD) and percent differences in D (%D) as calculated by TNR and TNR were respectively compared.

RESULTS

TNR and TNR were not significantly different across imaging modes (P=0.118) and were highly correlated (r=0.854; P<0.01). When stratification by tumor type (primary: n=27; metastatic: n=37) and location (left lobe: n=20; right lobe: n=44) was applied, significant TNR differences emerged only in the left-lobe group (TNR 5.9 TNR 4.7; P=0.015). Bland-Altman analysis demonstrated good agreement in both total and subgroup TNR measurements. The mean ΔTNR was 0.4±1.7, with %TNR ≤92.1%. Dliver calculations showed no significant intermodal difference (P=0.198). Analyses of ΔD and %D revealed maximum overestimations of 37.3 Gy (ΔD >0) and underestimations of 44.5 Gy (ΔD <0), with peak %D reaching 92.0%.

CONCLUSIONS

Comparison with Y PET/CT imaging indicated that Tc-MAA SPECT/CT could accurately reflect TNR and D in Y-SIRT. However, TNR may have the tendency to overestimate the true TNR, and appropriate dose adjustments should be considered during treatment planning. The differences in TNR observed in the left-lobe group and the potential differences in the primary group should be further analyzed in larger-sample studies.