Consistency assessment of voxel dosimetry using a Monte Carlo dose engine implemented in the updated MIM SurePlan™ MRT for 177Lu-DOTATATE therapy

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Background Patient-specific dosimetry for targeted radionuclide therapy (TRT) requires accurate estimation of three-dimensional absorbed dose distributions because radiopharmaceutical uptake and tissue density vary substantially within and between organs and tumors. A Monte Carlo (MC)-based dose engine has recently been implemented in an updated version of MIM SurePlan™ MRT as an alternative to conventional voxel S-value (VSV)-based dosimetry. This study assessed the numerical consistency of voxel dosimetry using the MC dose engine for 177 Lu-DOTATATE therapy. Methods We retrospectively analyzed 20 therapy cycles from five patients treated with 177 Lu-DOTATATE. Absorbed dose distributions generated using the MC dose engine were compared with those generated using the conventional VSV-based approach using identical quantitative SPECT/CT datasets, image registration, segmentation, and time-integrated activity maps. Mean absorbed doses were compared for organs and tumors using voxel-wise analysis, dose–volume histogram analysis, and Bland–Altman analysis. Results Mean absorbed dose estimates showed good agreement between the MC and VSV approaches for the kidneys, healthy liver, spleen, and bone, with differences generally within 1–2%. Agreement was particularly close in the healthy liver, whereas greater variability was observed in the lungs. Tumor absorbed dose estimates generated using the MC dose engine were consistently higher than those obtained using the VSV-based approach, with a mean difference of approximately 2.6%. Dose–volume histograms demonstrated similar overall absorbed dose distributions, although localized voxel-level differences were observed in heterogeneous regions and near tissue boundaries. Conclusion Voxel dosimetry using the MC dose engine implemented in the updated MIM SurePlan™ MRT demonstrated good numerical consistency with the conventional VSV-based approach under clinical conditions. Differences between the two methods were generally small for most evaluated organs and tumors, supporting the clinical applicability of the MC dose engine for voxel-level dosimetry in TRT.