Clinical Implementation of a Contour-Consistent Workflow for Activity Calculation and Post-Treatment SPECT/CT...

Image-based dosimetry has become increasingly important in yttrium-90 (⁹⁰Y) radioembolization, enabling quantitative assessment of absorbed-dose distributions within tumor and normal liver tissue. This retrospective report describes the clinical implementation of a contour-consistent workflow integrating cone-beam computed tomography (CT) segmentation with posttreatment single photon emission computed tomography (SPECT)/CT voxel-based dosimetry in 5 ⁹⁰Y glass microsphere cases. During treatment planning, contrast-enhanced cone-beam CT was used to identify and contour the perfused hepatic segment, and segment volume was used for activity calculation based on the Medical Internal Radiation Dose formalism. Posttreatment SPECT/CT was registered to cone-beam CT using rigid and deformable techniques, and cone-beam CT-derived contours were transferred for voxel-based dose reconstruction and dose-volume histogram (DVH) analysis. Segment volumes were generally comparable, whereas delivered mean segment dose varied relative to prescription, including underdosing in representative cases (eg, 87.66 Gy vs 130 Gy). DVH analysis demonstrated heterogeneous absorbed-dose distributions characteristic of ⁹⁰Y glass microsphere radioembolization, supporting clinically interpretable, segment-level posttreatment dosimetry.