Dose estimations for Iranian 11-year-old pediatric phantoms undergoing computed tomography examinations

Abstract

In order to establish an organ and effective dose database for Iranian children undergoing computed tomography (CT) examinations, in the first step, two Iranian 11-year-old phantoms were constructed from image series obtained from CT and magnetic resonance imaging (MRI). Organ and effective doses for these phantoms were calculated for head, chest, abdomen–pelvis and chest–abdomen–pelvis (CAP) scans at tube voltages of 80, 100 and 120 kVp, and then they were compared with those of the University of Florida (UF) 11-year-old male phantom. Depth distributions of the organs and the mass of the surrounding tissues located in the beam path, which shield the internal organs, were determined for all phantoms. From the results, it was determined that the main organs of the UF phantom receive smaller doses than the two Iranian phantoms, except for the urinary bladder of the Iranian girl phantom. In addition, the relationship between the anatomical differences and the size of the dose delivered was also investigated and the discrepancies between the results were examined and justified.

A Monte Carlo study on quantifying the amount of dose reduction by shielding the superficial organs of an Iranian 11-year-old boy

“…The voxel resolution was 0.15 cm × 0.15 cm × 0.3 cm, and the voxel array size was 300 × 170 × 490. [9] It should be mentioned that this phantom is anatomically close to the reference values reported by International Commission on Radiological Protection (ICRP) publication 89. [11] Therefore, the density and the elemental composition of organs and tissues of reference 11-year-old male voxel phantom developed at University of Florida (UF) were attributed to those of the Iranian phantom.…”

“…The third cylinder, with a diameter of 1.37 cm, defined a build-up cap, which was modeled as polyacetal plastic with a density of 1.43 g/cm 3 . [9] Figure 2 displays the CTDI phantom and the ion chamber used for model validation. Moreover, in Figure 3, a plot from the simulated CTDI phantom and ion chamber is illustrated.…”

“…Then, to incorporate the new geometries into MCNP4C, the whole model was voxelized applying the mentioned FORTRAN code developed in Ferdowsi University of Mashhad. [928]…”

“…Therefore, thickness of the shield is a determinant parameter that indicates how much each point of an organ or tissue is shielded from radiation impinging from X-ray source. [9] The preliminary results showed that if superficial organs are not the target of CT imaging, lead shields cannot interfere with the interpretation of the image and as the organ's shield is excluded from the imaging field, the presence of shield is inconsequential in terms of image quality. Given the results and more availability of lead, it was proposed as the beneficial shield for protecting the superficial organs.…”

“…[9] On the other hand, various organs are not local in one place, so the distances of their voxels from the surface vary significantly. Therefore, the amount of absorbed dose, which represents the averaged value of dose for all voxels of an organ, cannot determine the dose delivered to each voxel.…”