Internal dosimetry for paediatric patients: a GATE Monte Carlo study on UF/NCI phantoms

Internal dosimetry is essential in nuclear medicine, especially for paediatric patients, due to their heightened radiosensitivity. As direct measurement of energy deposition from radionuclides inside patients is not feasible, computational methods are employed to estimate absorbed dose distributions. This work presents a Monte Carlo-based dosimetric study using the GATE simulation toolkit on the UF/NCI voxelized paediatric phantom series. Specific Absorbed Fractions (SAFs) were computed for photons and electrons across energies from 10 keV to 0.5 MeV, considering source-target organ pairs relevant to clinical practice. Simulations were executed on the Marconi 100 HPC system within the INFN MIRACLE project, taking advantage of high parallelization to ensure statistical uncertainties below 5% for photon SAFs and below 1% for electron auto-SAFs. Results show SAF dependence on particle energy, organ size, inter-organ distance, and phantom age. SAFs, in general, show to decrease with increasing energy and age, while sex-based differences are negligible for the considered organ pairs. These data could provide a basis for improving activity administration planning in paediatric nuclear medicine, with the future possibility of extending such an analysis to additional organ pairs.