Estimativa da Dose de Entrada na Pele(DEP) para Espectros de Raios X Mamográficos Simulados

Abstract

Mammography is currently the most effective technique for the early diagnosis of breast cancer. The use of ionizing radiation is increasingly frequent in the diagnosis by images and it is necessary to have knowledge about dosimetry quantities that makes it possible to quantify the exposure of ionizing radiation in patients. In this study, the values of the dose at the entrance of the skin (DEP) were compared in practical tests and simulated tests, evaluating if the values of DEP for both tests are similar. Images were acquired in a Lorad Hologic brand, Selenia Dimensions model, with polymethylmethacrylate (PMMA) plates totaling thicknesses of 3, 5 and 7 centimeters. The images were acquired with Tungsten (W) target X-ray spectra and Rhodium (Rh) filter, varying the peak voltage (kVp) from 24 to 34 according to the PMMA thicknesses. The images were saved in the DICOM® standard, making it possible to obtain time-current (mAs) and DEP values for each image. X-ray spectra with Tungsten target (W) were simulated for the same peak voltages performed in the practical test, and with the use of statistical software it was possible to estimate the simulated skin entry dose (simulated DEP). For 3 cm PMMA and 26 kVp peak voltage the difference between simulated and practical DEP values was less than 2%. However, the difference between the DEP of the practical test and that of the simulated 24 kVp test was approximately 35%. In contrast, the difference between the DEP measured in the practical and simulated test for 28 kVp was 16% lower than the practice. For the 5-centimeter-thick images, the differences between the DEP values were less than 20% for all tensions, and for 28 kVp, the simulated DEP was approximately 3% smaller than the practical DEP. For the tests with 7 cm of PMMA and tensions of 30, 32 and 34 kVp, the differences between the DEP values in the practical and simulated tests were lower than ± 10% for all cases. Testing with X-ray spectra with other Target / Filter combinations must be performed so that you can tell whether the DEP values given by the DICOM® model standard are valid and can be used for quality control.