Calculation of Normalised Organ and Effective Doses to Adult Reference Computational Phantoms from Contemporary Computed Tomography Scanners

Abstract

The general-purpose Monte Carlo radiation transport code MCNPX has been used to simulate photon transport and energy deposition in anthropomorphic phantoms due to the x-ray exposure from the Philips iCT 256 and Siemens Definition CT scanners, together with the previously studied General Electric 9800. The MCNPX code was compiled with the Intel FORTRAN compiler and run on a Linux PC cluster. A patch has been successfully applied to reduce computing times by about 4%. The International Commission on Radiological Protection (ICRP) has recently published the Adult Male (AM) and Adult Female (AF) reference computational voxel phantoms as successors to the Medical Internal Radiation Dose (MIRD) stylised hermaphrodite mathematical phantoms that form the basis for the widely-used ImPACT CT Patient dosimetry tool. Comparisons of normalised organ and effective doses calculated for a range of scanner operating conditions have demonstrated significant differences in results (in excess of 30%) between the voxel and mathematical phantoms as a result of variations in anatomy. These analyses illustrate the significant influence of choice of phantom on normalised organ doses and the need for standardisation to facilitate comparisons of dose. Further such dose simulations are needed in order to update the ImPACT CT Patient Dosimetry spreadsheet for contemporary CT practice.

Updated estimates of typical effective doses for common CT examinations in the UK following the 2011 national review

“…Monte Carlo simulations Monte Carlo simulations have been performed [36][37][38] utilizing the general Monte Carlo N-Particle eXtended (MCNPX; Los Alamos National Laboratory, Los Alamos, NM) radiation transport code system v. 2.7.0, 39 installed on a dedicated personal computer cluster, comprising 10 calculation nodes and 1 server node. Simulations of dose have been completed in relation to a range of computational anthropomorphic phantoms, as discussed below, and to the measurement of CTDI (with a 100-mm pencil chamber) both at standard locations in the standard head and body CT dosimetry phantoms and also free-in-air on the axis of rotation.…”

How have advances in CT dosimetry software impacted estimates of CT radiation dose and cancer incidence? A comparison of CT dosimetry software: Implications for past and future research

“…For the reporting of effective dose, we averaged the male and female effective dose for comparison with the ImPACT hermaphrodite result. As a previous study had shown tube voltage affected the ratio of the organ and effective doses calculated by mathematical phantom software compared to the voxelised phantom software,[23] we restricted the analysis to cases with the most commonly used tube voltage cases in each protocol.…”

The dosimetric impact of including the patient table in CT dose estimates

“…Exceptions to the segmentation in the voxelized phantoms were the skeleton doses, since the endosteal cells and the red bone marrow are small compared to the voxel sizes and therefore voxels of these materials cannot be segmented. For the ICRP 110 phantoms (ICRP 2009) the dose to the skeleton and the dose to the red bone marrow were estimated in a similar way to Jansen and Shrimpton (2011). The endosteal cell dose (skeleton dose) was estimated by correcting individual skeleton doses with the ratio between the mass of the endosteal cells and mass of that individual skeleton.…”