Interpretation of the large-deformation high-spin bands in select A=158-168 nuclei

The high-spin rotational bands in Hf-168 and the triaxial bands in Lu nuclei are analyzed using the configuration-constrained cranked Nilsson-Strutinsky (CNS) model. Special attention is given to the up-sloping extruder orbitals. The relative alignment between the bands which appear to correspond to triaxial shape is also considered, including the yrast ultrahigh-spin band in Er-158. This comparison suggests that the latter band is formed from rotation around the intermediate axis. In addition, the standard approximations of the CNS approach are investigated, indicating that the errors which are introduced by the neglect of off-shell matrix elements and the cutoff at nine oscillator shells (N-max = 8) are essentially negligible compared to other uncertainties. On the other hand, the full inclusion of the hexadecapole degree of freedom is more significant; for example it leads to a decrease of the total energy of similar to 500 keV in the triaxial superdeformed (TSD) region of Hf-168

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

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

Studying the effects of the lung mass on the absorbed dose to the lung due to the administration of

131I is a radiopharmaceutical used for the treatment of advanced lung cancer, resulting in high organ doses. The effects of the lung mass on the absorbed dose to the lung due to the administration of 131I were studied in this research. For this purpose, the lung was selected as the source of 131I. Furthermore, 98 similar mathematical phantoms, only different in their lung mass, were developed. The received dose per decay of 131I for each organ was calculated using MCNPX. The results indicate that for the electrons emitted from the decay of 131I, the dose changes proportionally to the inverse of the lung mass. Considering that the participation of the electrons resulting from the decay of 131I in the amount of the lung dose outweighs the photon participation by a great deal, changes in the dose for the sum of the electrons and photons per decay are proportional to the inverse of the lung mass, as for the electrons

3D imaging of the elemental concentration associated with a malignant tumor in breast cancer using Neutron Stimulated Emission Computed Tomography: a Monte Carlo simulation study

Three-dimensional imaging of a cancerous breast with NSECT was proposed for the first time in this study. An irradiation system in a clinically relevant situation was simulated using the MCNP code. In the reconstructed images, the location and boundary of the tumor were identified by four elements, especially by 39K, with the ratio of malignant to healthy pixel intensity of about 2.446 (p-value ≪ 0.01). The average glandular dose was lower than the reference levels, and was comparable with the dose of digital X-ray mammography and 3D tomosynthesis examinations

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

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

A study of the effect of the lung shape on the lung absorbed dose in six standard photon and neutron exposure geometries

According to the published results of radiation dosimetry studies, there are significant discrepancies in the organ absorbed doses of existing adult male phantoms. As stated, differences in the organ absorbed doses may be associated with the variations in the organs’ volumes, shapes and positions in the body frame. Therefore, this paper focuses on the effect of the lung shape on the lung absorbed dose by creating a series of voxel phantoms, in which the lung shape follows a statistical distribution. These phantoms were exposed to mono-energetic photons and neutrons in six standard irradiation geometries. The results show that when the phantom is irradiated by the low-energy photons, the effects of the lung shape on the lung absorbed dose are considerable (with an uncertainty of more than 100%). For the other irradiation conditions, the variation in the lung shape causes an uncertainty of less than 10% in the dose delivered to the lung

Can the same dose data be estimated from phantoms with different anatomies?

In this paper, the effect of additional adipose and muscle layers was investigated on the effective dose and the organ absorbed dose. Calculations were performed using the Monte Carlo N-Particle Transport Code (MCNP) and the ORNL mathematical phantom for external photon and neutron beams. Variations in adipose and muscle tissue thickness were modeled by adding layers of adipose and soft tissues around the torso of the phantom. The effective dose decreased by about 7%–40% when the thickness of the extra layer increased from 0.5 to 5 cm considering all photon energies (10 keV–10 MeV) and neutron energies (10–9–20 MeV) for anterior-posterior, posterior-anterior, left-lateral, right-lateral, rotation and isotropic irradiation geometries. The results calculated here were compared with those reported in previous studies such as those of the VIPMAN, NORMAN05, MASH-3 and ICRP reference voxel phantoms. Our data shows that adding proper adipose or muscle layers to two very different phantoms can cause similar effective dose values, and also more than half of the organ absorbed doses have satisfactory agreement