Large Air Cavities Research Articles

Feasibility of EPID Based In Vivo Dosimetry for On-Couch Adaptive Radiotherapy

CBCT-based online adaptive radiotherapy allows treatment plans to be tailored to the anatomy of the day. For this purpose, dose optimization and computation are performed on a synthetic CT (sCT), i.e., a density map of the planning CT deformably registered onto the acquired CBCT. Plan-specific quality assurance of adaptive treatment sessions is currently limited to the vendors own secondary dose calculation on the sCT. The use of EPID recordings promises to detect deviations in beam delivery or patient position, incorrect sCT data and anatomical changes. The purpose of this research was to evaluate the feasibility of using a new commercial technology available for in-vivo dose reconstruction based on EPID exit beam measurements. EPID images were recorded from on-couch adapted, hypofractionated treatment plans created for a prostate patient. Secondary dose calculation of the adapted plan and 3D reconstructions from EPID images of the absolute dose delivered to the patient were performed with the in-vivo dosimetry system. Comparison of reconstructed and planned delivery was conducted by means of gamma analysis and DVH metrics. Comparisons of the intended plan to a second volumetric check (collapsed cone - CC algorithm), and to the EPID in-vivo calculation, produced gamma passing rates averaged over the 7 fractions of 98.3% and 88.8% at TG-218/219 recommended criteria (Table 1). DVH metrics showed average deviations of -2.9% / -3.3% for PTV D95% and -1.2% / -0.2% for PTV D50% between intended dose and secondary / EPID in-vivo dose. The pronounced discrepancies for fraction 3 in terms of both reduced gamma passing rates and increased deviations for the EPID reconstructed dose coincide with a large air cavity in the rectum showing up in the patient's CBCT prior to treatment. Secondary dose calculation based on the density information of the CBCT as an additional option for QA confirmed origin and magnitude of this effect. In-vivo EPID dosimetry of adaptive clinical plans is feasible. It was shown exemplary that it reveals fractions with noticeable anatomical changes between the sCT and the patient anatomy during treatment. As new recommendations were published on in-vivo dosimetry through TG 307, the development of new clinical tools and evaluation of existing commercial solutions is essential, also in the context of the growing use of on-couch adaptive technology.

Wave-in-deck loads induced by regular wave impact: The role of compressible air entrainment

During the process of wave-in-deck when waves impacting a horizontal platform deck from below, large air cavity entrainment would be generated between the free wave surface and the deck. The air entrainments are compressed and expanded during the process of wave impacts. As the momentum and energy exchange medium in the interactions between waves and the structure, air entrainments conversely influence the forces on the deck, risking structural safety. The key to dealing with the air entrainment is the combination of the mass source wave method and pressure-based compressible technique in capturing the cavity volume variation. In this work, the advanced compressible two-phase model is first developed with our in-house solver to simulate a regular wave impacting a fixed flat plate. The air cavity kinematics/dynamics and their relationship with wave impact features in the process of wave-in-deck impacting are discussed, and the mechanism of the compression/expansion effect is carefully analysed. Two distinct impacting types, direct water impact and entrained-air impact, are identified in this work, and the larger wave impacting pressures in the latter situation with compressible air layer is demonstrated. The good comparison of the numerical results and laboratory data on pressure features reveals that the proposed model is capable of reproducing the nonlinear entrained-air wave impacts and accurate oscillating pressures on a flat deck for applications.

Effect of internal defects on the thermal conductivity of fiber-reinforced polymer (FRP): A numerical study based on micro-CT based computational modeling

Use of fiber-reinforced polymer (FRP) composite in structural and aerospace fields is often restricted in a heated service condition. The thermal-induced degradation of FRP can be complicated by the internal defects with geometrical irregularities. This highlights the need for new characterization methods capable of revealing the thermal conduction process of FRP with different types of defects. To this end, the present study establishes a state-of-the-art methodology, namely micro computed tomography based finite element analysis (μCT-based FEA), for evaluating the influence of internal defects on the thermal conductivity of FRP. The modelling work through μCT gains an insight into the actual three-dimensional (3D) meso-scale structures for various species of defects (void, needle-like cavity, air pocket/unfilled bug hole, and delamination) in FRP. From the numerical ‘virtual’ experiments, the simulated through-thickness thermal conductivities range from 0.2196 to 0.2270 W/(m·K), which are comparable with the experimental data from literature. The investigation also discovers that the unfilled bug hole and delamination decrease the effective thermal conductivity of FRP, while these defects can cause sub-surface heat concentration. In contrast, the needle-like cavity has negligible effect on the through-thickness thermal conductivity. Increasing the water saturation degree of defects leads to an exponential increase in the thermal conductivity of FRP, especially when a large air cavity or delamination is incorporated into the composite. Based on transient analysis, the relationship among temperature, heat flux intensity and exposure time is numerically determined. The research findings can motivate the applications of μCT-based FEA in quality inspection/control of manufactured polymer composite products and even in improving the thermal non-destructive testing methods for defect detection of field composite structures.

Experimental observations and modelling of sub-Hinze bubble production by turbulent bubble break-up

We present experiments on large air cavities spanning a wide range of sizes relative to the Hinze scale$d_{H}$, the scale at which turbulent stresses are balanced by surface tension, disintegrating in turbulence. For cavities with initial sizes$d_0$much larger than$d_{H}$(probing up to$d_0/d_{H} = 8.3$), the size distribution of bubbles smaller than$d_{H}$follows$N(d) \propto d^{-3/2}$, with$d$the bubble diameter. The capillary instability of ligaments involved in the deformation of the large bubbles is shown visually to be responsible for the creation of the small bubbles. Turning to dynamical, three-dimensional measurements of individual break-up events, we describe the break-up child size distribution and the number of child bubbles formed as a function of$d_0/d_{H}$. Then, to model the evolution of a population of bubbles produced by turbulent bubble break-up, we propose a population balance framework in which break-up involves two physical processes: an inertial deformation to the parent bubble that sets the size of large child bubbles, and a capillary instability that sets the size of small child bubbles. A Monte Carlo approach is used to construct the child size distribution, with simulated stochastic break-ups constrained by our experimental measurements and the understanding of the role of capillarity in small bubble production. This approach reproduces the experimental time evolution of the bubble size distribution during the disintegration of large air cavities in turbulence.

Thermal modeling of the convective heat transfer in the large air cavities of the 3D concrete printed walls

The cavity walls are a widely used construction system. They became popular in traditional masonry construction for their capacity to reduce the passage of moisture and improve the walls’ thermal performance. However, the latter only applied to narrow cavities with restricted internal air movement. Cavities are also present in emerging technologies, such as 3D concrete printed walls. However, the large cavities of the 3D printed concrete walls have high convective heat transfers that affect the envelope’s thermal performance. Therefore, the authors developed a conjugate heat transfer finite element model to study the large cavities in 3D printed concrete walls and determine the effect on the convective heat transfer of subdividing large cavities. The results show it is possible to reduce the heat flux four times, from 40.4 W/m2 to 9.1 W/m2, subdividing a large cavity into sixteen small ones. This reduction might be higher, increasing the number of cavity subdivisions. However, it is infeasible to restrict the air movements in unfilled air cavities over 25 mm wide for the Rayleigh numbers ≥ 105. Therefore, the practicality of minimizing heat transfer by subdividing large air cavities in 3D printed walls is limited.

Morbid Constellation of Osseous and Vascular Abnormalities in a Female Patient with Congenital Central Hypoventilation/Overgrowth Syndrome

Background: Congenital Central Hypoventilation Syndrome (CCHS), is a condition characterized by ventilatory impairment that results in arterial hypoxemia. Studies revealed that the vast majority of patients with CCHS are free from any associated pulmonary, cardiac or brainstem pathologies. Material and Methods: F.R is a 20 -year-old- Austrian-girl presented in my consultation seeking advice for her unpleasant clinical history. In her early life, seizures were the first serious clinical presentation. Followed later on with hypertension, bouts of respiratory dysfunction and impairment of consciousness. In 2019 she underwent surgical intervention to remove a 2 cm hamartoma (posterior upper aspect of the right thigh). Few years later, another hamartoma on the ventral side of the tongue has been identified as well. Early on, she received the diagnosis of Mediterranean fever syndrome and the geneticist encountered homozygosity to the MEFV M694V mutation as the reason behind the constellation of the current unpleasant symptomatology. Later on a presumptive diagnosis of Ehlers-Danlos syndrome-hypermobile type has been suggested in other Medical Institutions. We proceeded with our documentation via clinical and radiological phenotypic characterizations. Results: Clinical examination showed growth above the 97th percentile (overgrowth) with no specific facial dysmorphic features. She manifested generalized ligamentous hyper laxity. Her ligamentous hyperlaxity was compatible with 6 points out of 9 in correlation with Beighton scoring test. On the bases of skeletal survey; lateral skull radiograph showed features of mastoid and temporal bone characterized with extensive-pneumatization. Axial CT scan shows bilateral hyper-pneumatization of the temporal bones, demonstrating expansion of aerial spaces with loss of the bony trabeculae and thinning of the mastoid bone. Mastoid cells appear to be in communication with a large intracranial epidural air cavity in the temporal and parietal regions. Reformatted CT scan of temporal bone, through coronal and axial images, at the level of the cavum tympani and the mastoid, showed a defect in the right tegmen appeared as cloudy/ opaque lesions around the cavum and the surrounding air cells. Contrast- enhanced computed CT angiography of the cervical and cerebral vasculature showed unusual malalignment and spiral twisting along several vascular segments resulted in the mal-development of basilar artery stenosis without atherosclerosis. The current patient manifested overgrowth syndromic entity with a constellation of osseous and vascular abnormalities resulted in a clinical course of congenital central hypoventilation syndrome. Conclusion: The etiology behind the extension of pneumatization has most likely occurred because of defective ossification of the occipito-mastoid synchondrosis . The reason behind the extension of pneumatization into the occipital and parietal bone is probably due to incomplete closure of the occipito-mastoid synchondrosis, lambdoid and sagittal sutures, which usually close in early adulthood and later, even at the age of thirties. In our patient, we postulate that the history of multiple hamartomas and abnormal vascular phenotype in conjunction with extensive hyper-pneumatization of the skull were the main etiology behind her unpleasant course of her devastating ailment regardless the genetic results. Our impression is neither Mediterranean fever syndrome nor Ehlers-Danlos syndrome seem compatible with her current constellation of osseous and vascular abnormalities. The overall clinical and imaging findings are highly likely in connection with either one of the different types of overgrowth syndromes or might be a novel syndromic association. We believe that congenital central hypoventilation is a symptom complex rather than a diagnostic entity.

Bubble production by air filament and cavity breakup in plunging breaking wave crests

Air filaments and cavities in plunging breaking waves, generically cylinders, produce bubbles through an interface instability. The effects of gravity, surface tension and surface curvature on cylinder breakup are explored. A generalized dispersion relation is obtained that spans the Rayleigh–Taylor and Plateau–Rayleigh instabilities as cylinder radius varies. The analysis provides insight into the role of surface tension in the formation of bubbles from filaments and cavities. Small filaments break up into bubbles through a Plateau–Rayleigh instability driven through the action of surface tension. Large air cavities produce bubbles through a Rayleigh–Taylor instability driven by gravity and moderated by surface tension, which has a stabilizing effect. Surface tension, interface curvature and gravity are all important for cases between these two extremes. Predicted unstable mode wavenumber and bubble size show good agreement with direct numerical simulations of plunging breaking waves and air cylinders.

Evaluation of two-dimensional electronic portal imaging device using integrated images during volumetric modulated arc therapy for prostate cancer.

The aim of the study was to evaluate analysis criteria for the identification of the presence of rectal gas during volumetric modulated arc therapy (VMAT) for prostate cancer patients by using electronic portal imaging device (EPID)-based in vivo dosimetry (IVD). All measurements were performed by determining the cumulative EPID images in an integrated acquisition mode and analyzed using PerFRACTION commercial software. Systematic setup errors were simulated by moving the anthropomorphic phantom in each translational and rotational direction. The inhomogeneity regions were also simulated by the I'mRT phantom attached to the Quasar phantom. The presence of small and large air cavities (12 and 48 cm3) was controlled by moving the Quasar phantom in several timings during VMAT. Sixteen prostate cancer patients received EPID-based IVD during VMAT. In the phantom study, no systematic setup error was detected in the range that can happen in clinical (< 5-mm and < 3 degree). The pass rate of 2% dose difference (DD2%) in small and large air cavities was 98.74% and 79.05%, respectively, in the appearance of the air cavity after irradiation three quarter times. In the clinical study, some fractions caused a sharp decline in the DD2% pass rate. The proportion for DD2% < 90% was 13.4% of all fractions. Rectal gas was confirmed in 11.0% of fractions by acquiring kilo-voltage X-ray images after the treatment. Our results suggest that analysis criteria of 2% dose difference in EPID-based IVD was a suitable method for identification of rectal gas during VMAT for prostate cancer patients.

Exploring the advantages of photo-voltaic triple skin façade in hot summer conditions

A new skin of perforated metallic sheet is introduced in the cavity of a photo-voltaic double skin façade (PV-DSF) system for an efficient heat removal from the cavity without losing substantial light into the built space. Quantitative experimental analysis is conducted to evaluate its thermal and electrical performance for various combinations of ventilation modes, air cavities, and perforation ratios. The advantages of Photo-Voltaic Triple Skin Facade system (PV-TSF) over commonly used PV-DSF are also evaluated experimentally. The results showed that naturally ventilated PV-TSF provides lower temperatures and Solar Heat Gain Coefficient (SHGC) with slightly higher power when compared to no ventilation mode in PV-DSF system. The SHGC of the PV-DSF system can be reduced by nearly 4.7% with variation in air cavity (Thickness 50–200 mm); after which no noticeable improvement is observed. In the case of PV-TSF system, SHGC can be reduced by almost 14.7% compared to the PV-DSF system without significant loss of natural daylight into built space. Experimental results also showed that the reduction in perforation ratio from 60% to 20% reduced the SHGC by 3.8% with an average illuminance of 334 lux (minimum perforation, 20%). It was also observed that the addition of a perforated sheet can offset the large air cavity of a PV-DSF system. Therefore, the benefit of the PV-TSF system is profound as compared to PV-DSF.

An experimental study of cavity and Worthington jet formations caused by a falling sphere into an oil film on water

In this paper, air cavity and Worthington jet formations due to the entrance of a hydrophilic steel sphere into three different target liquids are studied. The liquids are water, silicone oil and silicone oil film on water. A high-speed camera is used to observe cavity and jet formations, and the resulting data is used to measure important parameters such as jet height, deep-seal time and deep-seal depth of the cavity. It was observed that no cavity forms after a hydrophilic sphere enters water. However, when a very thin layer of silicone oil is put on the water surface, a large air cavity and Worthington jet were observed. The results observed did not strongly vary with oil film thickness for the range studied in this work, and that as long as there is a layer of oil on water that wets the sphere surface before its entrance, an air cavity and jet will form. Additionally, an energy analysis is done for better understanding how kinetic energy of the sphere is transferred to the fluid. In the case of an oil film on water, the sphere lost its kinetic energy much more than when the target liquid was silicone oil or water. As a result, the fluid gained a significant amount of energy to form an air cavity which did not happen without oil film, and a Worthington jet of greater maximum height than the other two cases. Kinetic, surface and potential energies of the Worthington jet as it forms and reaches its peak are studied as well.

Slumped IGU’s with large airspaces: engineering challenges and solutions

Aside from external cladding pressure loads that are always considered in IGU design, a variety of unique factors must also be addressed when analyzing the structural performance of a slumped IGU with a large air cavity. These factors include the volume of air within the cavity, the stiffness and strength of the outer and inner lites of glass, elevation changes between the glass fabrication facility and the building site, temperature changes over time, fluctuations in barometric pressure, and increased stress on the secondary structural perimeter seal. Appropriate deflection limits for mullions or other elements supporting the IGU must also be established due to the increased stiffness of the IGU resulting from the slumped glass geometry. Engineering challenges related to the design of slumped IGU’s will be highlighted and explained using Nike’s new retail flagship store in New York City, Nike House of Innovation 000, as a case study for a dynamic facade featuring custom carved and slumped insulating glass units. Principal analysis methods, testing procedures, and a summary of the various software tools used to evaluate the slumped IGU’s will be provided. The solutions shown will illustrate how the fundamental design and engineering approach taken for Nike can be successfully applied to other projects that incorporate slumped IGU’s into their facades.

Violent water-structure interaction: Overtopping features and vertical loads on a fixed structure due to broken incident flows

This paper presents an alternative experimental study of the interaction of broken flows with a fixed structure, concerning the overtopping features and vertical loads over its deck. Wet dam-break tests were carried out to generate incoming flows. Synchronized measurements provided by high-speed cameras, water elevation and force sensors, were used to investigate the influence of tank length in overtopping behaviour and the patterns and loads formed by wet dam-break flows generated by different conditions. During some of the overtopping events analysed, large scale plunging waves were observed, hitting the deck directly and forming large air cavities. These events generated violent interactions with the structure, causing significant loads and chaotic behaviour over the deck, due to the combination of air cavity collapse, reactive splash and run-down. The present approach could be employed as an alternative to study interactions of broken incident flows with different types of fixed structures, allowing the acquisition of detailed data to compare analytical or numerical models.

Experimental and numerical investigation of thermal improvement of window frames

This article presents experimental and numerical determinations of thermal transmittance performed on three different types of window frames (vinyl, aluminium, and wooden) within the same insulated glass unit. Good agreement between experimental and numerical results was attained. Using the numerical models, thermal improvement techniques of the frames and their influence on thermal transmittance of frames were studied. The first thermal improvement technique was using the insulation materials inserted inside large air cavities. By filling the cavity of vinyl frame with the polyurethane foam, thermal transmittance of vinyl frame was lowered by 10%. The second technique was based on repeating the procedure with materials installed inside frames with the materials that have lower thermal conductivity. This technique can be applied on thermal breaks and on steel profiles inside cavities. The result of this thermal improvement (attained by replacing thermal break material with material that has lower thermal conductivity) was certain reduction of the thermal transmittance of frames, by 9%. Using stainless steel instead of the oxidized steel was reduction of the thermal transmittance of vinyl frame by 3%. For the case of wooden frames the influence of shifting glazing unit deeper into profile upon the thermal transmittance of the frame was analyzed. Installing the glass unit by 5 mm deeper into the wooden frame reduced glass thermal transmittance by 5%.

Infrasonic hearing in birds: a review of audiometry and hypothesized structure-function relationships.

The perception of airborne infrasound (sounds below 20 Hz, inaudible to humans except at very high levels) has been documented in a handful of mammals and birds. While animals that produce vocalizations with infrasonic components (e.g. elephants) present conspicuous examples of potential use of infrasound in the context of communication, the extent to which airborne infrasound perception exists among terrestrial animals is unclear. Given that most infrasound in the environment arises from geophysical sources, many of which could be ecologically relevant, communication might not be the only use of infrasound by animals. Therefore, infrasound perception could be more common than currently realized. At least three bird species, each of which do not communicate using infrasound, are capable of detecting infrasound, but the associated auditory mechanisms are not well understood. Here we combine an evaluation of hearing measurements with anatomical observations to propose and evaluate hypotheses supporting avian infrasound detection. Environmental infrasound is mixed with non-acoustic pressure fluctuations that also occur at infrasonic frequencies. The ear can detect such non-acoustic pressure perturbations and therefore, distinguishing responses to infrasound from responses to non-acoustic perturbations presents a great challenge. Our review shows that infrasound could stimulate the ear through the middle ear (tympanic) route and by extratympanic routes bypassing the middle ear. While vibration velocities of the middle ear decline towards infrasonic frequencies, whole-body vibrations - which are normally much lower amplitude than that those of the middle ear in the 'audible' range (i.e. >20 Hz) - do not exhibit a similar decline and therefore may reach vibration magnitudes comparable to the middle ear at infrasonic frequencies. Low stiffness in the middle and inner ear is expected to aid infrasound transmission. In the middle ear, this could be achieved by large air cavities in the skull connected to the middle ear and low stiffness of middle ear structures; in the inner ear, the stiffness of round windows and cochlear partitions are key factors. Within the inner ear, the sizes of the helicotrema and cochlear aqueduct are expected to play important roles in shunting low-frequency vibrations away from low-frequency hair-cell sensors in the cochlea. The basilar papilla, the auditory organ in birds, responds to infrasound in some species, and in pigeons, infrasonic-sensitive neurons were traced back to the apical, abneural end of the basilar papilla. Vestibular organs and the paratympanic organ, a hair cell organ outside of the inner ear, are additional untested candidates for infrasound detection in birds. In summary, this review brings together evidence to create a hypothetical framework for infrasonic hearing mechanisms in birds and other animals.

Spontaneous Tracheal Perforation as a Late Complication of Thoracic Irradiation

SESSION TITLE: Disorders of the Mediastinum 1 SESSION TYPE: Affiliate Case Report Poster PRESENTED ON: Tuesday, October 31, 2017 at 01:30 PM - 02:30 PM INTRODUCTION: Tracheal injuries are rare, serious conditions that could result in life-threatening complications including pneumothorax, pneumomediastinum, and mediastinitis. Non-traumatic tracheal injuries are rarely encountered. We report a case of spontaneous tracheal perforation associated with thoracic irradiation. CASE PRESENTATION: A 46 y/o male with history of esophageal cancer status post chemoradiation and esophagectomy eight years ago, admitted with respiratory failure requiring invasive mechanical ventilation. Chest xray showed chronic right upper lobe collapse, radiation fibrosis, and airspace opacities suggestive of multifocal pneumonia. He received appropriate antibiotics, and surgical tracheostomy after weaning failure. On fourth week of admission, he developed dyspnea and hypoxia. Computed tomography showed large right apical air cavity communicating with trachea & right main bronchus, & extensive radiation fibrosis. Flexible bronchoscopy confirmed a large posterior tracheal membrane perforation distal to tracheostomy tube, perforations in right mainstem bronchus, and main carina. Thoracic surgery was consulted, unfortunately patient expired after cardiopulmonary arrest during surgery. DISCUSSION: Etiology of tracheal injuries include blunt force trauma, penetrating wounds, and iatrogenic (endotracheal intubation, tracheostomy & bronchoscopy). Spontaneous tracheal perforations are exceedingly rare, there are few case reports of spontaneous tracheal injuries secondary to tracheobronchial infections1,2. Our patient’s tracheal injury is unlikely due to tracheostomy procedure given additional findings of perforations on right mainstem bronchus and carina. We therefore conclude that his tracheal injuries were largely related to severe tracheobronchial tissue weakening due to radiation induced fibrosis and necrosis. Although there are no comparison trials between surgical repair and conservative approach, surgical evaluation is recommended in all cases of tracheal injuries. Nonoperative management have been reported successful in some cases of traumatic tracheal injuries3. Endoscopy is recommended to exclude esophageal perforation. CONCLUSIONS: Spontaneous tracheal injuries are rare, diagnosis is confirmed with bronchoscopy, and surgical evaluation is recommended. Reference #1: Repair of Tracheal Aspergillosis Perforation Causing Tension Pneumothorax. Gonzalez et al Reference #2: Spontaneous Tracheal Rupture Associated with Acquired Tracheobronchomalacia. Tsunezuka et al Reference #3: Conservative Treatment of Tracheal Injuries. Beiderlinden et al DISCLOSURE: The following authors have nothing to disclose: Afoma King, Ilya Berim No Product/Research Disclosure Information

Intraoperative breast radiation therapy with image guidance: Findings from CT images obtained in a prospective trial of intraoperative high-dose-rate brachytherapy with CT on rails.

Intraoperative radiation therapy (IORT) is an increasingly popular approach to breast conserving therapy in the treatment of early-stage breast cancer. A drawback to IORT compared with postoperative adjuvant radiation therapy is that it is not performed using image guidance. Our aim was to report on how our institution's unique IORT workflow integrates CT image guidance and how these CT images were used intraoperatively to change applicator positioning. We retrospectively reviewed the first 29 patients who participated in a prospective clinical trial of breast IORT at our institution. All patients underwent lumpectomy, multicatheter balloon placement, intraoperative CT scan, and high-dose-rate brachytherapy treatment delivery to 12.5 Gy to 1 cm from the balloon surface. This report focuses on the intraoperative CT findings that led to clinical changes, followed by repeat CT for IORT treatment planning. After initial intraoperative CT, 7 patients underwent an additional intraoperative CT scan (24.1%). In 6 patients, the initial intraoperative CT scan identified large air cavities and/or poor tissue conformity. This defect could be improved in all patients with adjustment of the balloon applicator before planning and delivering IORT. Intraoperative CT scan was used in one patient to localize a biopsy clip and aided in excision to negative margin. In our study, intraoperative CT identifies actionable findings in breast IORT, including residual tumor or errors in applicator positioning, in almost 25% of patients. Clinical results of the described trial will serve to further validate this image-guided approach to IORT.

SU‐E‐T‐791: Validation of a Determinant Based Photon Transport Solver in Dose Perturbed By Diverse Media

Purpose:To validate a determinant based photon transport solver in dose imparted within different transition zone between different medium.Methods:Thickness (.2cm,.5cm, 1cm, 3cm) from various materials (Air ‐ density=0.0012g/cm3, Cork‐0.19g/cm3, Lung‐0.26g/cm3, Bone‐1.85g/cm3, Aluminum (Al)‐2.7g/cm3, Titanium (Ti)‐4.42g/cm3, Iron (Fe)‐8g/cm3) were sandwiched by 10cm solid water. 6MV were used to study the calculation difference between a superposition photon beam model (AAA) and the determinant based Boltzmann photon transport solver (XB) at the upstream (I) and downstream boarder (II) of the medium, within the medium (III), and at far distance downstream away from medium (IV). Calculation was validated with available thickness of Air, Cork, Lung, Al, Ti and Fe. Results are presented as the ratio of the dose at the point with medium perturbation to the same point dose without perturbation.Results:Zone I showed different backscatter enhancement from high‐density materials within the 5mm of the upstream border. AAA showed no backscatter at all, XB showed good agreement beyond 1mm upstream (1.18 vs 1.14, 1.09 vs 1.10, and 1.04 vs 1.05 for Fe, Ti, and Fe, respectively). Zone II showed a re‐buildup after exiting high‐density medium and Air but no build up for density close to water in both of the measurement and XB. AAA yielded the opposite results in Zone II. XB and AAA showed in Zone III very different absorption in high density medium and the Air. XB and measurement had high concordance regarding photon attenuation in Zone IV. AAA showed less agreement especially when the medium was Air or Fe.Conclusion:XB compared well with measurement in regions 1mm away from the interface. Planning using XB should be beneficial for External Beam Planning in situations with large air cavity, very low lung density, compact bone, and any kind of metal implant.

Wide-band millimetre-wave antenna based on Si and suspended BCB membrane

This paper presents the design, fabrication and characterization of a millimetre-wave wide-band patch antenna integrated on silicon (Si) and using a BCB membrane suspended over a deep cavity etched in the Si substrate. The antenna structure consists of a top patch on a Si cap, a bottom patch on a BCB membrane and a ground plane in the cavity. The antenna takes advantage of the coupling between the stacked patches and the large air cavities to achieve a wide impedance bandwidth around 60 GHz. The bottom patch is implemented using electroplating on the suspended BCB membrane which is transferred through our wafer-level transfer technique over the cavity. The size of the realized antenna is 3.5 × 2.8 × 0.6 mm3. The fabricated antenna showed a reflection coefficient lower than ?7 dB from 49.5 GHz to more than 67 GHz (30 % fractional bandwidth) and an experimental gain in the order of 7 dBi at 60 GHz in good agreement with the simulation (7.5 dBi).

Distinguishing features of shallow angle plunging jets

Numerical simulations employing an algebraic volume-of-fluid methodology are used to study the air entrainment characteristics of a water jet plunging into a quiescent water pool at angles ranging from θ = 10° to θ = 90° measured from the horizontal. Our previous study of shallow angled jets [S. S. Deshpande, M. F. Trujillo, X. Wu, and G. L. Chahine, “Computational and experimental characterization of a liquid jet plunging into a quiescent pool at shallow inclination,” Int. J. Heat Fluid Flow 34, 1–14 (2012)]10.1016/j.ijheatfluidflow.2012.01.011 revealed the existence of a clearly discernible frequency of ingestion of large air cavities. This is in contrast with chaotic entrainment of small air pockets reported in the literature in case of steeper or vertically plunging jets. In the present work, the differences are addressed by first quantifying the cavity size and entrained air volumes for different impingement angles. The results support the expected trend – reduction in cavity size (D43) as θ is increased. Time histories of cavity volumes in the vicinity of the impingement region confirm the visual observations pertaining to a near-periodic ingestion of large air volumes for shallow jets (10°, 12°), and also show that such cavities are not formed for steep or vertical jets. Each large cavity (defined as Dc/Dj ≳ 3) exists in close association with a stagnation point flow. A local mass and momentum balance shows that the high stagnation pressure causes a radial redirection of the jet, resulting in a flow that resembles the initial impact of a jet on the pool. In fact, for these large cavities, their speed matches closely Uimpact/2, which coincides with initial cavity propagation for sufficiently high Froude numbers. Furthermore, it is shown that the approximate periodicity of air entrainment scales linearly with Froude number. This finding is confirmed by a number of simulations at θ = 12°. Qualitatively, for steeper jets, such large stagnation pressure region does not exist, and the deflection of the entire incoming jet is non-existent. In fact, for θ = 25°, 45°, 90°, the jet penetrates the pool nearly undisturbed and consequently large cavities are not formed.

SU-E-T-518: Effect of Statistic Uncertainty On DVH and Dose Mass Histogram (DMH) Derived Dose Indices (DI) for Head and Neck IMRT-Monte Carlo(MC) Treatments

Purpose: The use of DMH as an alternative method to validate the treatment plans of the head and neck region has been investigated in the past[1].For patient geometry contains large air cavities,high statistical uncertainties were found in dose distributions calculated using MC method in air cavities and tissues that surround air cavities.These previous studies reported that the shape of DMH is less affected by the statistical uncertainty than DVH. But the authors did not verify the differences between DIs derived from DVH and DMH.In the present work we compare the DIs derived from DVHs and DMHs based on dose distributions calculated using MC method and different levels of statistical precision. Methods: Six IMRT plans were calculated using the EGS4 based MCSIM code.MCSHOW allows to built DVHs and DMHs from dose distributions calculated with different statistical uncertainty(from 0.5% to 10%). The DIs were derived from the DVHs and DMHs for the target and critical structures (cord, chiasm, larynx,brainstem and parotid). Results: Comparing the values (averaged over 6 patients) of target DMH (0.5%) and DMH (2%) we found that all DIs (D05, D95, Mp, Dmax) do not differ in more than 0.7%. By comparison of target DVH (0.5%) and target DVH (2%) we observed differences of about 14% on the value of Dmax and V95 changes in more than 3%. We verified that the statistical effect is not significant (less than 1%) for the DVH of critical structures. Conclusion: The DIs derived from DMHs are not strong dependent on the statistical uncertainty of the dose values as those derived from DVHs. Our results confirmed the previous idea that DMH is a better parameter than DVH for evaluating treatment plans calculated by MC simulations in low density regions. [1]-G.Mora et al., MCTP 2009,Cardiff 2009.