Assessing dose variability in PET/CT-based voxel dosimetry for Y-90 radioembolization

Purpose: This study aimed to evaluate the impact of calculation parameters on organ dose coefficients in image-based dosimetry for Yttrium-90 (Y-90) transarterial radioembolization (TARE). Methods: Patient-specific dose coefficient maps were generated using PET/CT images from six hepatocellular carcinoma patients using TOPAS Monte Carlo simulations. To reduce spurious activity, PET values below varying thresholds (0, 50, and 100 kBq/mL) were excluded, and the effect of these thresholds on dose coefficients was assessed. The influence of CT Hounsfield unit conversion was examined by varying the number of materials from 1 to 24. The effects of dose calculation method, physics models, and voxel sizes on dose coefficients were systematically investigated. Results: Spurious activity was the dominant factor influencing the variability of the dose coefficient. Adapting the activity threshold resulted in the mean difference of 38.8 (15.2 %), 3.3 (11.9 %), and 0.1 (6.5 %) Gy/GBq for the tumor, liver, and lungs. The mean difference of lung dose coefficient (1.1 Gy/GBq, 67.2 %) between single and 24 materials. The dose calculation method, physics model, and PET voxel size had a relatively small impact on variability. Conclusions: This study systematically evaluated potential factors contributing variability of dose coefficient after Y-90 TARE, with spurious activity identified as a major factor.