Construction of realistic hybrid computational fetal phantoms from radiological images in three gestational ages for radiation dosimetry applications

Radiation exposure and associated radiation risks are major concerns for fetal development for pregnant patients who undergo radiation therapy or diagnostic imaging procedures. In order to accurately estimate the radiation dose to the fetus and assess the uncertainty of fetal position and rotation, three hybrid computational fetus phantoms were constructed using magnetic resonance imaging (MRI) for each fetus model as a starting point to construct a complete anatomically accurate fetus, gravid uterus, and placenta. A total of 27 fetal organs were outlined from radiological images via the Velocity Treatment Planning System. The DICOM-Structure set was imported to Rhinoceros software for further reconstruction of 3D fetus phantom model sets. All fetal organ masses were compared with ICRP-89 reference data. Our fetal model series corresponds to 20, 31, and 35 weeks of pregnancy, thus covering the second and third trimester. Fetal positions and locations were carefully adapted to represent the real fetus locations inside the uterus for each trimester of pregnancy. The new series of hybrid computational fetus models together with pregnant female models can be used in evaluating fetal radiation doses in diagnostic imaging and radiotherapy procedures

An overview of exposure parameters, dose measurements and strategies for dose reduction in pediatric CT examinations

CT scanning technology is a valuable tool to diagnose many diseases; however, the level of the radiation dose is a source of concern, especially for children. CT scan systems and dose measurement methods have evolved over the years; but reported pediatric effective doses (EDs) have sometimes exceeded the annual dose limit recommended by the ICRP (1 mSv per year for persons under 18 years) (ICRP, 2007a). Efforts have been made to reduce organ doses and EDs by adjusting the scan parameters. This paper describes the determinants of the ED, and the dose reduction techniques in pediatric imaging from the early age of CT examinations until now. The first epidemiological results regarding the associated risk of cancer are also briefly presented

Modeling the adult female phantom in the supine and prone postures and initial dose assessment in breast cancer diagnosis with Neutron Stimulated Emission Computed Tomography

In this study, the delivered dose for breast cancer diagnosis by NSECT was assessed in two different configurations, using a model of a human whole body, which was simulated in the supine and prone positions. In the system with the phantom in the prone posture, the adjacent organ doses were considerably decreased. In total irradiation, the breast equivalent dose was less than 10 mSv, which is received in a typical chest CT scan. To apply NSECT as a low-dose clinical imaging system, improving the detection system is required

Dose estimation in reference and non-reference pediatric patients undergoing computed tomography examinations: a Monte Carlo study

The global increase in the number of computed tomography (CT) examinations have enhanced concerns regarding stochastic radiation risks to patients, especially for children. Considering that cancer risk is cumulative over a lifetime and each CT examination contributes to the lifetime exposure, there is a need for a better understanding of radiation-induced cancer incidence and mortality, and better dose estimates. Accordingly, some authors estimated organ and effective dose in reference phantoms, but still there is a critical need to expand these data to larger groups of non-reference children. As an initial step to address this issue, in this study organ and effective doses were calculated in common CT procedures in non-reference pediatric phantoms and were compared with those of reference phantoms with the similar ages. Thirteen pediatric phantoms, BABY CHILD, five voxel-based UF pediatric phantoms (B-series) and six phantoms developed at The Foundation for Research on Information Technologies in Society (IT’IS) were implemented into MCNP. According to the results, there were no consistent differences between the doses of organs exposed indirectly and effective doses of these three phantom types, but it was observed that for organs located in the scan region, there was a relation between absorbed doses and pediatric age group, as expected. Generally, using the results of this study one can estimate the absorbed doses more accurately. But it should be noted that these low expansion data are not comprehensive enough for finding a reasonable relationship between phantom size and effective dose except in chest-abdomen-pelvis (CAP) imaging

The contributions of source regions to organ doses from incorporated radioactive iodine

The separate contributions of all source regions to organ doses from 131I and 123I administered to the body were calculated using voxelized reference phantoms. The photon and electron components of organ doses were also evaluated for each source region. The MCNPX Monte Carlo particle transport code was utilized for dose calculations. All organs and tissues of male and female phantoms were taken into account as source regions with their corresponding cumulated activities. The results showed that cumulated activities assigned to source regions and inter-organ distances were two factors that strongly affected the contribution of each source to the organ dose. The major contribution of the dose to the main source regions arose from self-irradiation of electrons, while for nearby organs it was due to photons emitted by the main source organs. In addition, self-irradiation plays an important role in the dose delivered to most target organs for lower thyroid uptakes

Evaluating the effects of statistical changes on internal dosimetry

Currently, internal dosimetry evaluations are performed using reference computational phantoms. There are significant discrepancies in the organ absorbed doses regarding the variations in organ mass. In this study, to investigate the effects of changes in the lung mass on the results of internal dosimetry, 98 similar mathematical phantoms were developed, so that the masses of their lungs changed with a Gaussian distribution. The lung was selected as the source. Doses delivered to the organs/tissues for photons with different energy levels, and also per decay of 131I, were calculated using MCNPX. The results showed that changing the mass of the lung has effects on the dose of the lung, especially for low-energy photons and electrons resulting from the decay of 131I. According to the statistical distribution in terms of the SAF as a function of the lung mass, the average value of organ SAFs and the coefficient of variations were estimated. The uncertainties of the lung SAF due to the lung mass variation can be described by the coefficient of variation (CV), which changed from 9% to 19%. This occurs for photon energy in the range of 10 to 4000 keV. This figure stands at 18% per decay of 131I