Experimental and Monte Carlo dose assessment in paediatric computed tomography

Dose assessment in computer tomography (CT) can be performed by Monte Carlo (MC) computer simulation programs. These simulations use realistic computational models of human bodies to estimate organ doses and therefore perform patient-specific dosimetry. In this study, the MC code MCNP 6.2 has been used to calculate the radiation dose for children under a CT scan procedure. For the implementation of the model in the code, an external source subroutine has been developed. An X-ray source with a rectangular centre beam shape was simulated, rotating upwards along the inner surface of a cylinder in a helical manner. To define the key parameters, the user could then specify what kind of CT scanning protocol should be selected. For model validation, MC simulations with a model of the one-year-old male ATOM 704 phantom were done and the results were compared with the outcome of measurements of the phantom using thermoluminescence dosimeters (TLDs) at a GE Brightspeed 16 CT model. A realistic computational model of a 1-year old child was finally used to calculate organ doses. Through the comparison of the data simulated and measured, the implemented CT model was validated and it can now support further investigations of organ doses to children of different body sizes. • A new MCNP 6.2 subroutine was developed and verified to model a helical scanner • Measurements with ATOM 704 paediatric phantom and TLD-100 dosimeters were simulated • Voxelized version of ATOM 704 phantom was created from tomographic images • Organ absorbed dose in ATOM 704 and ICRP 1-year-old reference phantoms was studied