Investigation of dose distributions of computed tomography with cylindrical polymethyl methacrylate (PMMA) phantoms

Abstract

Background: This study aimed to investigate the effect of patient’s size on the distribution and amount of dose of computed tomography (CT) based on standard cylindrical polymethyl methacrylate (PMMA) phantoms. Methods: In this study, a two-dimensional film dosimetry method was represented via using radiographic films; the effect of patient’s size on the distribution and the amount of received dose was investigated using cylindrical phantoms with 10, 16, 24 and 32 cm diameters. The cylindrical phantoms were made of polymethyl methacrylate sheets. By proper calibration, two-dimensional distribution of the dose was measured using film dosimetry in these phantoms in a single axial rotation. Findings: The dose distribution in the cylindrical phantoms was not symmetric particularly in closer points to the surface. The received dose in the cross-section of phantom increased with beam width. The received dose in the central part of phantom decreased more than its surface by the increment of phantom diameter. Specially, using a cylindrical phantom with diameter of16 cm, the received dose in the central part of the phantom decreased to 65 of its surface dose; whereas this percentage for cylindrical phantoms with diameters of 24 and 32 cm was 45 and 35, respectively. Conclusion: The dose distribution in the cross-section of the pediatric patients is more uniform. It is highly dependent on the couch attenuation and overscan, leading to asymmetry of the dose distribution. The received dose in the pediatric patients would be more than adults for the same mAs. © 2015, Isfahan University of Medical Sciences(IUMS). All rights reserved.