Determinación de las distribuciones de dosis asociadas a una tomografía helicoidal de tórax mediante simulaciones Monte Carlo

Abstract

In this work, the characteristics of the dose distributions in the lungs, heart and bones of an anonymous patient subject to a thoracic helical CT with the Brilliance Big Bore (BBB) scanner from SOLCA-Quito Oncology Hospital were analyzed using Monte Carlo simulations with the x platform GATE. In the simulations, the thoracic region was symmetrically irradiated around the central cross section during 12 seconds employing the following parameters: 120 kV p, 200 mAs, NT= 24 mm and pitch= 0.69. With these conditions, the dose distributions were heterogeneous in the thoracic region, showing doses between ∼ 3.82 mGy and ∼ 172 mGy. The average doses were estimated, rendering the following values: 28.83 ± 0.005 [mGy], 31.52 ± 0.01 [mGy] and 58.90 ± 0.005 [mGy] in lungs, heart and bones respectively. For each organ, these values differ 4 % at the most from the D50 doses estimated with the dosevolume histograms (DVH). Dose heterogeneity in the phantom is evident from the fact that dose values depend on Hounsfield units and coordinates of y and z. However, there is not a simple model that explains properly the relationship between dose and image parameters.