Desenvolvimento de objeto simulador pediátrico para dosimetria em varreduras de tomografia computadorizada do tórax

Abstract

Computed tomography is a diagnostic imaging technique with vast clinical indications in medical practice and greatly contributes to the collective radiation doses from radiologic diagnosis. The dissemination of this radiological technique has promoted a significant increase of the absorbed dose in patients due to the diagnosis. Therefore, it is important to improve protocols with smaller doses without impairing the image diagnostic quality, since any additional risk, no matter how small, is unacceptable if it does not benefit the patient. The knowledge of the distribution of the dose given to a child is important when one thinks about varying the acquisition parameters, aiming for dose reduction. The risks of stochastic effects are greater in children due to tissue radiosensitivity coupled with a longer life expectancy. In this work, a cylindrical phantom made of polymethylmethacrylate was used, to simulate an adult chest while a second oblong shaped phantom was developed using the same material and based on the chest dimensions of an 8-year-old pediatric patient. A comparative study was performed between chest scans realized on two computerized tomography scans. The central portion of the two phantoms was successively irradiated and, using a pencil ionization chamber, the absorbed dose was measured at five different points in each phantom. From the measurements, Volumetric Dose Index values were obtained for the 10-cm scan of the central object region, in helical mode. The scans were performed using the chest acquisition protocols used by the radiological service, both with a 120 kV X-ray tube supply voltage. This work made it possible to compare the variation of the absorbed dose between patients with distinct chest volumes and the patient dose variation between two devices when used for the generation of images with the same diagnostic purpose