Dosimetric study of chest computerized tomography in childhood using phantoms

The dissemination of computed tomography (CT) promoted a significant increase in the dose absorbed by patients due to the diagnosis. Therefore, it is essential to improve protocols, seeking lower doses, without prejudice to the diagnostic quality of the image. The risks of stochastic effects are higher for children due to tissue radiosensitivity combined with longer life expectancy. In this work, a cylindrical simulator object representing an adult thorax made of polymethyl methacrylate was used, and simulated objects of the same material were developed, in oblong shape including axillary regions, based on the dimensions of the chest of a pediatric patient. A comparative study was performed between chest scans performed on two CT scans at different radiology services. The central slice of the simulating objects was irradiated successively and, using a pencil-type ionization chamber, absorbed dose measurements were made at five distinct points of each simulating object. From the measurements, the values of weighted and volumetric dose indices were obtained for the 10 cm scan of the central region of the objects, in helical mode. The scans were performed with the chest acquisition protocols used by the radiodiagnostic services, both for a 120 kV X-ray tube supply voltage. This study compared the absorbed dose variation between patients with different chest volumes and the patient dose variation between two devices when used for imaging with the same diagnostic objective, with the purpose of proposing optimized protocols. The results indicated that the protocols defined for children are oversized and need to be corrected to optimize the dose deposited in these patients