Internal dosimetry Monte Carlo study of TARE treatments: a comparison between GATE and GAMOS focused on lung dosimetry and background correction

Purpose: Three-dimensional internal dosimetry is increasingly used in planning Trans-Arterial Radio-Embolization (TARE) of HepatoCellular Carcinoma (HCC). Among the existing calculation approaches, Monte Carlo (MC) simulation is the gold standard. Aim of this work was to carry out a dosimetric study of TARE cases, starting from SPECT-CT acquisitions, to compare the results obtained with GATE and GAMOS codes for liver and lungs and to highlight the effect of different approaches in background corrections. Materials and Methods: We developed MC simulations by means of GATE (Geant4 Application for Emission Tomography) and GAMOS (GEANT4-based Architecture for Medicine-Oriented Simulations), employing CT scans for defining digital phantoms and SPECT scans for modelling radionuclide distributions. Moreover, we adopted threshold-based filtering procedures on SPECT scans through 3DSlicer software, in order to carry out simulations with filtered SPECTs for a more accurate evaluation of the dose values and background. Three-dimensional absorbed dose maps, Dose Volume Histograms (DVHs) and mean absorbed doses in Volumes of Interest (VOIs), corresponding to lungs and liver, were calculated, using both for unfiltered and filtered SPECTs via either GATE and GAMOS. Results: Comparison between GATE and GAMOS results highlights the effects of their different phantom density assignment procedures. A relevant reduction of dose background outside the patient body and of dose in air-rich anatomical regions, particularly in lungs, was achieved when filtered SPECT images were considered. Conclusions: This study shows that the background of SPECT images used as input data for MC simulations can produce a non-negligible influence on dose overestimation in the regions outside the patient and in air-rich and low density organs and tissues, such as lungs.