Size-specific dose estimates in chest, abdomen, and pelvis CT examinations of pediatric patients.

PURPOSE: Size-specific dose estimates (SSDEs) are the latest focus of interest among medical physicists studying radiation dose to the patient in computed tomography (CT). This study aims to make conversions from CTDIvol to SSDE and investigate the relationship between mean SSDE (SSDE) and central SSDE (SSDEcenter) values for pediatric patients of different age groups undergoing chest, abdomen, and pelvis scans. METHODS: In this retrospective study, we examined 105 consecutive pediatric CT exams of chest, abdomen, and pelvis (CAP) classified in 3 separate groups according to age: 0-5 years, 6-10 years, and 11-16 years. A MATLAB program was developed to determine SSDE values for each patient along 6 subregions: chest, abdomen, pelvis, chest and abdomen, abdomen and pelvis, and CAP. SSDE values derived over the slice at the center of each scan range (SSDEcenter) were also recorded. SSDE and corresponding SSDEcenter results were compared for each age group. RESULTS: Root mean square differences (RMSD) between SSDE and SSDEcenter values ranged between 0.13 mGy and 2.1 mGy through all groups and subregions, corresponding to 1.2% and 11%, respectively. CONCLUSION: In pediatric CT exams involving CAP region, CTDIvol and the water equivalent diameter at the middle of the scan range can be used to provide a reasonable estimate of mean SSDE with an RMSD of 11% at most.

Experimental and Simulation Analysis of Radiation of the Beta Emitting Sources in a Magnetic Field.

OBJECTIVE: The behavior of beta particles under the magnetic field was investigated both theoretically and experimentally based on the assumption of reducing the damage to the normal tissues created by using magnetic field in radionuclide therapy. METHODS: A water-filled spherical medium and a beta particle source was formed by using Geant4 simulation software for the theoretical study. After applying a homogenous magnetic field, the volume of points at which the particles interact with the medium was calculated by determining particle range. The range of beta particles was examined using yttrium-90 source and Gafchromic films for the experimental study. The setup was kept in normal room conditions and in the magnetic resonance imaging device. Then the irradiated films were analyzed by creating isodose curves. RESULTS: With the increase of the magnetic field, the number of hits at the center was increased, but the number of hits at the outer boundaries decreased inversely proportional to the strength of the magnetic field. The change perpendicular to the magnetic field was greater as compared to the change parallel to the magnetic field. The volume of hits of beta particles got smaller with the increase of the magnetic field. CONCLUSION: When magnetic field is increased, the decrease in the number of interactions at the outer boundaries became more pronounced in the perpendicular direction to the magnetic field. The effect of magnetic field was more apparent for higher energy beta particles than lower energy particles.