Importing High-fidelity MIDA Phantom into Geant4 for Calibrating in Vivo Measurement of Internal Radioactivity

In vivo measurement has been widely employed to monitor internal contamination in potentially exposed personals, wherein detection efficiency calibration is an important step to convert the counting statistics into radioactivity. Though the physical anthropomorphic phantoms are dominantly employed in the calibration step, there are growing interests in replacing them with computational counterparts due to their flexibility. Moreover, thanks to the fine resolution of medical imaging, such as CT and MRI, the anatomical fidelity of computational phantom has reached an unprecedented precision. However, because the cost of developing such high-fidelity computational phantoms is tremendous, they are often not shared. In contrast, the MIDA model, developed by FDA and IT’IS foundation is publicly available and has been frequently used in MRI and biomedical studies concerning electromagnetics. In this work, we report the detailed procedures of importing the MIDA phantom into Geant4 platform, which mainly includes two major steps: first, assigning the material composition based on ICRP Publication 23 and 110, and ICRU 46; second, converting the voxel matrix into a file in g4dcm format that can be recognized by the DICOM program of Geant4. To demonstrate its application, we show the detection efficiency calibration of Am-241 deposited in the skull and compare the results against experiments. We consider our work would facilitate the wide adoption of high-fidelity computational phantom in the detection efficiency calibration for in vivo measurement.