Development and evaluation of a clinical model for lung cancer patients using stereotactic body radiotherapy (SBRT) within a knowledge-based algorithm for treatment planning

The purpose of this study was to describe the development of a clinical model for lung cancer patients treated with stereotactic body radiotherapy (SBRT) within a knowledge-based algorithm for treatment planning, and to evaluate the model performance and applicability to different planning techniques, tumor locations, and beam arrangements. 105 SBRT plans for lung cancer patients previously treated at our institution were included in the development of the knowledge-based model (KBM). The KBM was trained with a combination of IMRT, VMAT, and 3D CRT techniques. Model performance was validated with 25 cases, for both IMRT and VMAT. The full KBM encompassed lesions located centrally vs. peripherally (43:62), upper vs. lower (62:43), and anterior vs. posterior (60:45). Four separate sub-KBMs were created based on tumor location. Results were compared with the full KBM to evaluate its robustness. Beam templates were used in conjunction with the optimizer to evaluate the model\u27s ability to handle suboptimal beam placements. Dose differences to organs-at-risk (OAR) were evaluated between the plans gener-ated by each KBM. Knowledge-based plans (KBPs) were comparable to clinical plans with respect to target conformity and OAR doses. The KBPs resulted in a lower maximum spinal cord dose by 1.0 ± 1.6 Gy compared to clinical plans, p = 0.007. Sub-KBMs split according to tumor location did not produce significantly better DVH estimates compared to the full KBM. For central lesions, compared to the full KBM, the peripheral sub-KBM resulted in lower dose to 0.035 cc and 5 cc of the esophagus, both by 0.4Gy ± 0.8Gy, p = 0.025. For all lesions, compared to the full KBM, the posterior sub-KBM resulted in higher dose to 0.035 cc, 0.35 cc, and 1.2 cc of the spinal cord by 0.2 ± 0.4Gy, p = 0.01. Plans using template beam arrangements met target and OAR criteria, with an increase noted in maximum heart dose (1.2 ± 2.2Gy, p = 0.01) and GI (0.2 ± 0.4, p = 0.01) for the nine-field plans relative to KBPs planned with custom beam angles. A knowledge-based model for lung SBRT consisting of multiple treatment modalities and lesion loca-tions produced comparable plan quality to clinical plans. With proper training and validation, a robust KBM can be created that encompasses both IMRT and VMAT techniques, as well as different lesion locations

Characterization and evaluation of 25 MV electronic portal imaging for accurate localization of intra- and extracranial stereotactic radiosurgery

2.5 MV electronic portal imaging, available on Varian TrueBeam machines, was characterized using various phantoms in this study. Its low-contrast detectability, spatial resolution, and contrast-to-noise ratio (CNR) were compared with those of conventional 6 MV and kV planar imaging. Scatter effect in large patient body was simulated by adding solid water slabs along the beam path. The 2.5 MV imaging mode was also evaluated using clinically acquired images from 24 patients for the sites of brain, head and neck, lung, and abdomen. With respect to 6 MV, the 2.5 MV achieved higher contrast and preserved sharpness on bony structures with only half of the imaging dose. The quality of 2.5 MV imaging was comparable to that of kV imaging when the lateral separation of patient was greater than 38 cm, while the kV image quality degraded rapidly as patient separation increased. Based on the results of patient images, 2.5 MV imaging was better for cranial and extracranial SRS than the 6 MV imaging

Characteristics of a novel treatment system for linear accelerator–based stereotactic radiosurgery

The purpose of this study is to characterize the dosimetric properties and accuracy of a novel treatment platform (Edge radiosurgery system) for localizing and treating patients with frameless, image-guided stereotactic radiosurgery (SRS) and stereotactic body radiotherapy (SBRT). Initial measurements of various components of the system, such as a comprehensive assessment of the dosimetric properties of the flattening filter-free (FFF) beams for both high definition (HD120) MLC and conical cone-based treatment, positioning accuracy and beam attenuation of a six degree of freedom (6DoF) couch, treatment head leakage test, and integrated end-to-end accuracy tests, have been performed. The end-to-end test of the system was performed by CT imaging a phantom and registering hidden targets on the treatment couch to determine the localization accuracy of the optical surface monitoring system (OSMS), cone-beam CT (CBCT), and MV imaging systems, as well as the radiation isocenter targeting accuracy. The deviations between the percent depth-dose curves acquired on the new linac-based system (Edge), and the previously published machine with FFF beams (TrueBeam) beyond Dmax were within 1.0% for both energies. The maximum deviation of output factors between the Edge and TrueBeam was 1.6%. The optimized dosimetric leaf gap values, which were fitted using Eclipse dose calculations and measurements based on representative spine radiosurgery plans, were 0.700 mm and 1.000 mm, respectively. For the conical cones, 6X FFF has sharper penumbra ranging from 1.2–1.8 mm (80%-20%) and 1.9–3.8 mm (90%-10%) relative to 10X FFF, which has 1.2–2.2mm and 2.3–5.1mm, respectively. The relative attenuation measurements of the couch for PA, PA (rails-in), oblique, oblique (rails-out), oblique (rails-in) were: -2.0%, -2.5%, -15.6%, -2.5%, -5.0% for 6X FFF and -1.4%, -1.5%, -12.2%, -2.5%, -5.0% for 10X FFF, respectively, with a slight decrease in attenuation versus field size. The systematic deviation between the OSMS and CBCT was -0.4 ± 0.2 mm, 0.1± 0.3mm, and 0.0 ± 0.1 mm in the vertical, longitudinal, and lateral directions. The mean values and standard deviations of the average deviation and maximum deviation of the daily Winston-Lutz tests over three months are 0.20 ± 0.03 mm and 0.66 ± 0.18 mm, respectively. Initial testing of this novel system demonstrates the technology to be highly accurate and suitable for frameless, linac-based SRS and SBRT treatment

Micromechanical model for damage and failure of brittle materials : application to polycrystalline ice and concrete

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1995.Includes bibliographical references.by Jinkoo Kim.Ph.D

Simplified Life Cycle Cost Estimation of Low-Rise Steel Buildings Using Fundamental Period

In the current study, a simplified seismic life cycle cost (LCC) estimation procedure is proposed utilizing the mean values of the structure’s main input variables. The main input variables of the building are used for constructing a relationship between the structural fundamental period (T) and an average estimation of the LCC (LCCavg). Using the actual building properties related to damage probability, the T–LCCavg relationship is used to obtain the final LCC (LCCfin). The equivalent single degree of freedom (ESDOF) model and SAC-FEMA framework are utilized for damage probability calculation. The dispersion measure in demand is approximately calculated based on the mean plus one standard deviation of the seismic hazard response spectrum, and, then, verified through nonlinear time history (NLTH) analyses of the original structure. Five and three-story steel buildings are used as case studies for verification of the proposed method. The analysis results indicate that the proposed procedure provides reasonable LCC estimations for low-rise buildings dominated by the fundamental mode of vibration

Some Recent Developments in the Vibration Control and Structure Health Monitoring

Vibration is a common phenomenon when a structure is exposed to mechanical or environmental actions [...

Fuzzy Sensitivity Analysis of Structural Performance

Despite the versatility and widespread application of fuzzy randomness in structural and mechanical engineering, less attention has been paid to the formulation of sensitivity analysis for this uncertainty model. In this research, a brief review of the application of sensitivity analyses in structural engineering is provided, and then the concept of local sensitivity analysis is developed for the fuzzy randomness theory. Several sensitivity tests based on the classical probability theory are extended to this uncertainty model, namely, Monte Carlo simulation (MCS), tornado diagram analysis (TDA), and first-order second-moment method (FOSM). The multidisciplinary application of these methods in engineering is shown using a numerical example, a truss structure, and finally, seismic performance evaluation of a framed structure from a full-scale experimental test. The way of visualizing the results is also provided, which helps the interpretation and better understanding. The results show that the established tools can provide detailed insight into the uncertainty of fuzzy random models. The formulated fuzzy local sensitivity can show how the output uncertainty is affected by the uncertainty of input parameters and the effectiveness of each parameter on the output variability. The provided visualization technique can show variability, the fuzziness of variability, and the order of most influential parameters. Furthermore, efficient methods such as TDA and FOSM can substantially reduce the computational time compared to the MCS while providing an acceptable trade-off for accuracy

Adaptive linear analysis for inelastic seismic design of reinforced concrete moment frames

An adaptive linear analysis method for inelastic seismic design of reinforced concrete moment frames is developed adopting the well-known concept of incremental linear approximation for non-linear analysis. A series of linear analyses are performed for multiple lateral loading steps. After performing the linear analysis for each loading step, the analysis model of the structure is modified for the linear analysis of the next loading step addressing the current distribution of plastic hinges. By simply summing up the results of all piecewise linear analyses, the inelastic force and deformation demands of the members are directly determined. The proposed method is applied to the inelastic seismic design of regular and irregular reinforced concrete special moment frames and the design results are verified by comparing with the results of non-linear analysis. The adaptive linear analysis, which is aimed at application to the preliminary seismic design where the non-linear analysis is not preferred, can directly account for the effects of inelastic behaviour such as plastic mechanism of structure, moment redistribution between members and plastic deformations of members.*AIK, 2009, KOR BUILD COD STRUCT*ACI, 2008, ACI31808Park H, 2005, J STRUCT ENG-ASCE, V131, P1355, DOI 10.1061/(ASCE)0733-9445(2005)131:9(1355)*MID IT, 2005, MID GEN AN MAN*ASCE, 2000, 356 ASCE FEMAPRIESTLEY MJN, 2000, P 12 WORLD C EARTHQPRAKASH V, 1993, UCBSEMM9317