In Silico Validation of MCID Platform for Monte Carlo-Based Voxel Dosimetry Applied to 90Y-Radioembolization of Liver Malignancies

Abstract

The aim was the validation of a platform for internal dosimetry, named MCID, based on patient-specific images and direct Monte Carlo (MC) simulations, for radioembolization of liver tumors with 90Y-labeled microspheres. CT of real patients were used to create voxelized phantoms with different density and activity maps. SPECT acquisitions were simulated by the SIMIND MC code. Input macros for the GATE/Geant4 code were generated by MCID, loading coregistered morphological and functional images and performing image segmentation. The dosimetric results obtained from the direct MC simulations and from conventional MIRD approach at both organ and voxel level, in condition of homogeneous tissues, were compared, obtaining differences of about 0.3% and within 3%, respectively, whereas differences increased (up to 14%) introducing tissue heterogeneities in phantoms. Mean absorbed dose for spherical regions of different sizes (10 mm ≤ r ≤ 30 mm) from MC code and from OLINDA/EXM were also compared obtaining differences varying in the range 7–69%, which decreased to 2–9% after correcting for partial volume effects (PVEs) from imaging, confirming that differences were mostly due to PVEs, even though a still high difference for the smallest sphere suggested possible source description mismatching. This study validated the MCID platform, which allows the fast implementation of a patient-specific GATE simulation, avoiding complex and time-consuming manual coding. It also points out the relevance of personalized dosimetry, accounting for inhomogeneities, in order to avoid absorbed dose misestimations.

Normal organ dosimetry for thyroid cancer patients treated with radioiodine as part of the multi-centre multi-national Horizon 2020 MEDIRAD project

“…Dosimetry team A (DTA, Centre de Recherches en Cancérologie de Toulouse) performed dosimetry calculations from data acquired at centres 2 to 4 using OpenDose3D [ 24 – 26 ], an extension to 3DSlicer [ 27 , 28 ] developed as part of the OpenDose project [ 29 ]. The extension relies on the existing open source architecture of 3DSlicer designed for medical image analysis and includes modules specifically designed for molecular radiotherapy (MRT) dosimetry such as calculation of absorbed dose (rates) from 3D maps of density and cumulated activity (activity) and the integration of time-dependent parameters including activity (to provide cumulated activity or time-integrated activity), or absorbed dose rates (to provide the absorbed dose).…”

Personalized Dosimetry in the Context of Radioiodine Therapy for Differentiated Thyroid Cancer

“…Increased availability of SPECT-CT and PET-CT scanners and consequently improved image quality allowed for a more direct approach, using the measured patient activity distribution from PET/CT or SPECT/CT images, superimposed over the anatomy as obtained by the CT portion of the imaging scan. Such voxelized dosimetry approaches use Monte Carlo or point-kernel methods to calculate maps of the spatial distribution of absorbed dose [ 95 , 96 , 97 , 98 , 99 , 100 ]. Detailed descriptions of how these measurements should be made using quantitative imaging methods have been extensively treated and reported in the literature [ 101 , 102 ].…”

Applications of Medical Physics

“…In the frame of internal dosimetry, the study by Milano et al [18] aims at the validation of a platform, named MCID, based on patient-specific images and direct Monte Carlo (MC) simulations for internal dosimetry in the radioembolization of liver tumors with 90 Y-labeled microspheres. The validated platform allows the fast implementation of a personalized MC dosimetry, based on patient imaging data.…”