Mendes, MCosta, FFigueira, CMadeira, PTeles, PVaz, P2018-08-062018-08-062015-07Radiat Prot Dosimetry. 2015 Jul;165(1-4):175-81.http://hdl.handle.net/10400.17/3011This work reports on the use of two different Monte Carlo codes (GEANT4 and MCNPX) for assessing the dose reduction using bismuth shields in computer tomography (CT) procedures in order to protect radiosensitive organs such as eye lens, thyroid and breast. Measurements were performed using head and body PMMA phantoms and an ionisation chamber placed in five different positions of the phantom. Simulations were performed to estimate Computed Tomography Dose Index values using GEANT4 and MCNPX. The relative differences between measurements and simulations were <10 %. The dose reduction arising from the use of bismuth shielding ranges from 2 to 45 %, depending on the position of the bismuth shield. The percentage of dose reduction was more significant for the area covered by the bismuth shielding (36 % for eye lens, 39 % for thyroid and 45 % for breast shields).engAlgorithmsBreastComputer SimulationComputersEquipment DesignFemaleHumansLens, CrystallineMonte Carlo MethodPhantoms, ImagingProtective DevicesRadiation DosageRadiation ProtectionReproducibility of ResultsThyroid GlandTomography Scanners, X-Ray ComputedTomography, X-Ray ComputedBismuthHSJ IMAjournal article10.1093/rpd/ncv059