A Monte Carlo study of organ and effective doses of cone beam computed tomography (CBCT) scans in radiotherapy

Cone-beam CT (CBCT) scans utilized for image guided radiation therapy (IGRT) procedures have become an essential part of radiotherapy. The aim of this study was to assess organ and effective doses resulting from new CBCT scan protocols (head, thorax, and pelvis) released with a software upgrade of the kV on-board-imager (OBI) system. Influence of the scan parameters that were changed in the new protocols on the patient dose was also investigated. Organ and effective doses for protocols of the new software (V2.5) and a previous version (V1.6) were assessed using Monte Carlo (MC) simulations for the International Commission on Radiological Protection (ICRP) adult male and female reference computational phantoms. The number of projections and the mAs values were increased and the size of the scan field was extended in the new protocols. Influence of these changes on organ and effective doses of the scans was investigated. The OBI system was modelled in EGSnrc/BEAMnrc, and organ doses were estimated using EGSnrc/DOSXYZnrc. The MC model was benchmarked against experimental measurements. Organ doses resulting from the V2.5 protocols were higher than those of V1.6 for organs that were partially or fully inside the scans fields, and increased by (3 to 13)%, (10 to 77)%, and (13 to 21)% for the head, thorax, and pelvis protocols for both phantoms, respectively. As a result, effective doses rose by 14%, 17%, and 16% for the male phantom, and 13%, 18%, and 17% for the female phantom for the three scan protocols, respectively. The scan field extension for the V2.5 protocols contributed significantly in the dose increases, especially for organs that were partially irradiated such as the thyroid in head and thorax scans and colon in the pelvic scan. The contribution of the mAs values and projection numbers was minimal in the dose increases, up to 2.5%. The field size extension plays a major role in improving the treatment output by including more markers in the field of view to match between CBCT and CT images and hence setting up the patient precisely. Therefore, a trade-off between the risk and benefits of CBCT scans should be considered, and the dose increases should be monitored. Several recommendations have been made for optimization of the patient dose involved for IGRT procedures

On convergence rates of suprema in the presence of non-negligible trends

We investigate the convergence rates for the maximal deviation distribution of kernel estimates from the true density. The convergence rates for related Gaussian fields are also investigated. We consider the optimal choice of the smoothing parameter in the sense of Konakov and Piterbarg (1994) and in doing so we take into account a non-negligible trend. It is shown that the convergence rates depend on the asymptotic behaviour of the Laplace type integrals over a small neighbourhood of the manifold of points at which the trend attains its maximal value. Using integration over the level sets (Leray-Gel'fand differential forms) it is proved that the convergence rates are tipically logarithmically slow, even if the rates are to be uniform over as few as three points. Some improved approximations with power rates of convergence are also obtained. (orig.)Available from TIB Hannover: RR 5549(103)+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Quantitative comparison of volumetric modulated arc therapy and intensity modulated radiotherapy plan quality in sino-nasal cancer

The aim of this study was to compare various dosimetric parameters of dynamic mlc intensity modulated radiotherapy (IMRT) plans with volumetric modulated arc therapy (VMAT) plans for sino-nasal cancers, which are rare and complex tumors to treat with radiotherapy. IMRT using five fields, coplanar in the sagittal plane and VMAT employing two coplanar arc plans were created for five patients. The plans were assessed by comparing Conformity Index and Sigma Index (dose homogeneity) in the Planning Target Volume (PTV) and through comparison of dose-volume characteristics to the following organs at risk (OARs): Spinal cord, brainstem, eye, ipsilateral and contralateral optic nerve and the volume of brain receiving 10% of the prescribed dose (V10%). The total monitor units required to deliver the plan were also compared. Conformity Index was found to be superior in VMAT plans for three patients and in IMRT plans for two patients. Dose homogeneity within the PTV was better with VMAT plans for all five cases. The mean difference in Sigma Index was 0.68%. There was no significant difference in dose between IMRT and VMAT plans for any of the OARs assessed in these patients. The monitor units were significantly reduced in the VMAT plan in comparison to the IMRT plan for four out of five patients, with mean reduction of 66%. It was found in this study that for the treatment of sino-nasal cancer, VMAT produced minimal, and statistically insignificant improvement in dose homogeneity within the PTV when compared with IMRT. VMAT plans were delivered using significantly fewer monitor units. We conclude in this study that VMAT does not offer significant improvement of treatment for sino-nasal cancer over the existing IMRT techniques, but the findings may change with a larger sample of patients in this rare condition

Chloride: a menace to advance oxidation processes (AOPs)

With the advent of technology, mobile devices are becoming powerful and they are widely used as convenient computing devices. In order to develop high quality application in a short period while overcoming the limitations and challenges in mobile development, strong knowledge and understanding of the design purpose are the key factors in developing well- designed applications. Good design ensures that crashes or harmful actions can be prevented as well as increasing users’ satisfaction. By implementing design patterns, developers can cater wide variety of users whereby they do not have to redevelop similar application for users who are using different types of devices. Application can be developed in a short period as developer can reuse design patterns to develop new application in similar domain. Our proposed work aims to implement design patterns to overcome limitations of current techniques and increase efficiency, usability and reusability in mobile application development