Beschreibung:
<jats:title>Abstract</jats:title>
<jats:p>
<jats:italic>Objective</jats:italic>. <jats:sup>177</jats:sup>Lu is one of the most employed isotopes in targeted radionuclide therapies and theranostics, and 3D internal dosimetry for such procedures has great importance. Voxel S-Values (VSVs) approach is widely used for this purpose, but VSVs are available for a limited number of voxel dimensions. The aim of this work is to develop an analytic model for the calculation of <jats:sup>177</jats:sup>Lu-VSVs in any cubic voxelized geometry of practical interest. <jats:italic>Approach</jats:italic>. Monte Carlo (MC) simulations were implemented with the toolkit GAMOS to evaluate VSVs in voxelized geometries of soft tissue from a source of <jats:sup>177</jats:sup>Lu homogeneously distributed in the central voxel. Nine geometric setups, containing 15 × 15 × 15 cubic voxels of sides <jats:italic>l</jats:italic> ranging from 2 mm to 6 mm, in steps of 0.5 mm, were considered. For each <jats:italic>l</jats:italic>, the VSVs computed as a function of the ‘normalized radius’, <jats:italic>R</jats:italic>
<jats:sub>
<jats:italic>n</jats:italic>
</jats:sub> = <jats:italic>R/l</jats:italic> (with <jats:italic>R</jats:italic> = distance from the center of the source voxel), were fitted with a parametric function. The dependencies of the parameters as a function of <jats:italic>l</jats:italic> were then fitted with appropriate functions, in order to implement the model for deducing <jats:sup>177</jats:sup>Lu-VSVs for any <jats:italic>l</jats:italic> within the aforementioned range. <jats:italic>Main results</jats:italic>. The MC-derived VSVs were satisfactorily compared with literature data for validation, and the VSVs computed with the analytic model agree with the MC ones within 2% for <jats:italic>R</jats:italic>
<jats:sub>
<jats:italic>n</jats:italic>
</jats:sub> ≤ 2 and within 6% for <jats:italic>R</jats:italic>
<jats:sub>
<jats:italic>n</jats:italic>
</jats:sub> > 2. <jats:italic>Significance</jats:italic>. The proposed model enables the easy and fast calculation, with a simple spreadsheet, of <jats:sup>177</jats:sup>Lu-VSVs in any cubic voxelized geometry of practical interest, avoiding the necessity of implementing <jats:italic>ad-hoc</jats:italic> MC simulations to estimate VSVs for specific voxel dimensions not available in literature data.</jats:p>