Distribution of the radiation dose in multislice computer tomography of the chest : phantom study

Background: The most commonly used form of reporting doses in multislice computed tomography involves a CT dose index per slice and dose-length product for the whole series. The purpose of this study was to analyze the actual dose distribution in routine chest CT examination protocols using an antropomorphic phantom. Material and Methods: We included in the analysis readings from a phantom filled with thermoluminescent detectors (Art Phantom Canberra) during routine chest CT examinations (64 MDCT TK LIGHT SPEED GE Medical System) performed using three protocols: low-dose, helical and angio-CT. Results: Mean dose values (mSv) reported from anterior parts of the phantom sections in low-dose/helical/angio-CT protocols were as follows: 3.74; 16.95; 30.17; from central parts: 3.18; 14.15; 26.71; from posterior parts: 3.01; 12.47; 24.98 respectively. Correlation coefficients for mean doses registered in anterior parts of the phantom between low-dose/helical, low-dose/angio-CT and helical/angio-CT protocols were 0.49; 0.63; 0.36; from central parts: 0.73; 0.66; 0.83, while in posterior parts values were as follows: 0.06; 0.21; 0.57. Conclusions: The greatest doses were recorded in anterior parts of all phantom sections in all protocols in reference to largest doses absorbed in the anterior part of the chest during CT examination. The doses were decreasing from anterior to posterior parts of all sections. In the long axis of the phantom, in all protocols, lower doses were measured in the upper part of the phantom and at the very lowest part