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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Portal dosimetry for VMAT using integrated images obtained during treatment

Purpose: Portal dosimetry provides an accurate and convenient means of verifying dose delivered to the patient. A simple method for carrying out portal dosimetry for volumetric modulated arc therapy (VMAT) is described, together with phantom measurements demonstrating the validity of the approach. Methods: Portal images were predicted by projecting dose in the isocentric plane through to the portal image plane, with exponential attenuation and convolution with a double-Gaussian scatter function. Appropriate parameters for the projection were selected by fitting the calculation model to portal images measured on an iViewGT portal imager (Elekta AB, Stockholm, Sweden) for a variety of phantom thicknesses and field sizes. This model was then used to predict the portal image resulting from each control point of a VMAT arc. Finally, all these control point images were summed to predict the overall integrated portal image for the whole arc. The calculated and measured integrated portal images were compared for three lung and three esophagus plans delivered to a thorax phantom, and three prostate plans delivered to a homogeneous phantom, using a gamma index for 3% and 3 mm. A 0.6 cm{sup 3} ionization chamber was used to verify the planned isocentric dose. The sensitivity of this method to errors in monitor units, field shaping, gantry angle, and phantom position was also evaluated by means of computer simulations. Results: The calculation model for portal dose prediction was able to accurately compute the portal images due to simple square fields delivered to solid water phantoms. The integrated images of VMAT treatments delivered to phantoms were also correctly predicted by the method. The proportion of the images with a gamma index of less than unity was 93.7% ± 3.0% (1SD) and the difference between isocenter dose calculated by the planning system and measured by the ionization chamber was 0.8% ± 1.0%. The method was highly sensitive to errors in monitor units and field shape, but less sensitive to errors in gantry angle or phantom position. Conclusions: This method of predicting integrated portal images provides a convenient means of verifying dose delivered using VMAT, with minimal image acquisition and data processing requirements.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

The design and fabrication of two portal vein flow phantoms by different methods

Purpose: This study outlines the design and fabrication techniques for two portal vein flow phantoms. Methods: A materials study was performed as a precursor to this phantom fabrication effort and the desired material properties are restated for continuity. A three-dimensional portal vein pattern was created from the Visual Human database. The portal vein pattern was used to fabricate two flow phantoms by different methods with identical interior surface geometry using computer aided design software tools and rapid prototyping techniques. One portal flow phantom was fabricated within a solid block of clear silicone for use on a table with Ultrasound or within medical imaging systems such as MRI, CT, PET, or SPECT. The other portal flow phantom was fabricated as a thin walled tubular latex structure for use in water tanks with Ultrasound imaging. Both phantoms were evaluated for usability and durability. Results: Both phantoms were fabricated successfully and passed durability criteria for flow testing in the next project phase. Conclusions: The fabrication methods and materials employed for the study yielded durable portal vein phantoms.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

SU-F-J-26: Performance of 2.5MV Portal Imaging in Comparison with KV X-Ray and 6MV and Flattening-Filter-Free 6MV Portal Imaging

Purpose: To assess image quality and imaging dose of 2.5MV electronic portal imaging in comparison to kV imaging and 6MV and Flattening-Filter-Free 6MV (6MVFFF) portal imaging using a DMI imager. Methods: Quantitative assessment of image quality was performed with Leeds and Las Vegas test phantoms in conjunction with qualitative evaluation of clinical patient images for kV imaging and 2.5MV, 6MV and 6MVFFF portal imaging. High and low contrast resolutions were evaluated and imaging doses were measured using these x-rays. Phantom test was performed both in air and in solid water. Clinical patient portal images were also reviewed and qualitatively assessed for these three imaging MV energies. Results: Among the 28 objects in Las Vegas phantom, 16, 17 and 26 of them were resolved using Low Dose technique and 18, 22 and 26 were resolved using High Quality technique with 6MV, 6MVFFF and 2.5MV, respectively. The number of Leeds low contrast objects resolved by 6MV, 6MFFFF and 2.5MV was 6, 15 and 18 with Low Dose technique and 14, 17 and 18 with High Quality technique, respectively. When the test phantoms were embedded in 20cm thick solid water, the results were noticeably affected, but the performance of 2.5MV was still substantially better than 6MV and 6MVFFF. Imaging dose with 2.5MV measured at 10 cm depth was about half of that with 6MV or 6MVFFF. Clinical patient portal images were reviewed and qualitatively assessed for different sites including brain, head-and-neck, chest and pelvis. 2.5MV imaging provided more details and substantially higher contrast. Conclusion: While portal imaging with 6MVFFF provides noticeably better image quality than that with 6MV, the performance of 2.5MV portal imaging is substantially better than both 6MV and 6MVFFF in terms of high and low contrast resolutions as well as lower imaging dose. 2.5MV imaging provides near kV imaging quality.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Z-portal dark matter

We propose to generalize the extensions of the Standard Model where the Z boson serves as a mediator between the Standard Model sector and the dark sector χ. We show that, like in the Higgs portal case, the combined constraints from the recent direct searches restrict severely the nature of the coupling of the dark matter to the Z boson and set a limit m{sub χ}≳200 GeV (except in a very narrow region around the Z-pole region). Using complementarity between spin dependent, spin independent and FERMI limits, we predict the nature of this coupling, more specifically the axial/vectorial ratio that respects a thermal dark matter coupled through a Z-portal while not being excluded by the current observations. We also show that the next generation of experiments of the type LZ or XENON1T will test Z-portal scenario for dark matter mass up to 2 TeV. The condition of a thermal dark matter naturally predicts the spin-dependent scattering cross section on the neutron to be σ{sub χn}{sup SD}≃10{sup −40} cm{sup 2}, which then becomes a clear prediction of the model and a signature testable in the near future experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Portal Vein Stenting for Portal Biliopathy with Jaundice

Portal biliopathy refers to obstruction of the bile duct by dilated peri- or para-ductal collateral channels following the main portal vein occlusion from various causes. Surgical shunt operation or endoscopic treatment has been reported. Herein, we report a case of portal biliopathy that was successfully treated by interventional portal vein recanalization.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Thermal and non-thermal production of dark matter via Z{sup ′}-portal(s)

We study the genesis of dark matter in the primordial Universe for representative classes of Z{sup ′}-portals models. For weak-scale Z{sup ′} mediators we compute the range of values of the kinetic mixing allowed by WMAP/PLANCK experiments corresponding to a FIMP regime. We show that very small values of δ (10{sup −12}≲δ≲10{sup −11}) are sufficient to produce the right amount of dark matter. We also analyse the case of very massive gauge mediators, whose mass m{sub Z{sup ′}} is larger than the reheating temperature, T{sub RH}, with a weak-scale coupling g{sub D} to ordinary matter. Relic abundance constraints then impose a direct correlation between T{sub RH} and the effective scale Λ of the interactions: Λ∼10{sup 3}−10{sup 5}×T{sub RH}. Finally we describe in some detail the process of dark thermalisation and study its consequences on the computation of the relic abundance.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Higgs portal vector dark matter for GeV scale γ-ray excess from galactic center

We show that the GeV scale γ-ray excess from the direction of the Galactic Center can be naturally explained by the pair annihilation of Abelian vector dark matter (VDM) into a pair of dark Higgs bosons (VV→ϕϕ), followed by the subsequent decay of ϕ into bb{sup -bar} or ττ{sup -bar}. All the processes are described by a renormalizable VDM model with the Higgs portal, which is naturally flavor-dependent. Some parameter space of this scenario can be tested at the near future direct dark matter search experiments such as LUX and XENON1T.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Fast transit portal dosimetry using density-scaled layer modeling of aSi-based electronic portal imaging device and Monte Carlo method

Purpose: Fast and accurate transit portal dosimetry was investigated by developing a density-scaled layer model of electronic portal imaging device (EPID) and applying it to a clinical environment. Methods: The model was developed for fast Monte Carlo dose calculation. The model was validated through comparison with measurements of dose on EPID using first open beams of varying field sizes under a 20-cm-thick flat phantom. After this basic validation, the model was further tested by applying it to transit dosimetry and dose reconstruction that employed our predetermined dose-response-based algorithm developed earlier. The application employed clinical intensity-modulated beams irradiated on a Rando phantom. The clinical beams were obtained through planning on pelvic regions of the Rando phantom simulating prostate and large pelvis intensity modulated radiation therapy. To enhance agreement between calculations and measurements of dose near penumbral regions, convolution conversion of acquired EPID images was alternatively used. In addition, thickness-dependent image-to-dose calibration factors were generated through measurements of image and calculations of dose in EPID through flat phantoms of various thicknesses. The factors were used to convert acquired images in EPID into dose. Results: For open beam measurements, the model showed agreement with measurements in dose difference better than 2% across open fields. For tests with a Rando phantom, the transit dosimetry measurements were compared with forwardly calculated doses in EPID showing gamma pass rates between 90.8% and 98.8% given 4.5 mm distance-to-agreement (DTA) and 3% dose difference (DD) for all individual beams tried in this study. The reconstructed dose in the phantom was compared with forwardly calculated doses showing pass rates between 93.3% and 100% in isocentric perpendicular planes to the beam direction given 3 mm DTA and 3% DD for all beams. On isocentric axial planes, the pass rates varied between 95.8% and 99.9% for all individual beams and they were 98.2% and 99.9% for the composite beams of the small and large pelvis cases, respectively. Three-dimensional gamma pass rates were 99.0% and 96.4% for the small and large pelvis cases, respectively. Conclusions: The layer model of EPID built for Monte Carlo calculations offered fast (less than 1 min) and accurate calculation for transit dosimety and dose reconstruction.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Roadside Tracker Portal-less Portal Monitor

This report documents the full development cycle of the Roadside Tracker (RST) Portal-less Portal monitor (Fig. 1) funded by DHS DNDO. The project started with development of a proof-of-feasibility proto-type, proceeded through design and construction of a proof-of-concept (POC) prototype, a test-and-evaluation phase, participation in a Limited Use Exercise that included the Standoff Radiation Detections Systems developed under an Advanced Technology Demonstration and concluded with participation in a Characterization Study conducted by DNDO.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Superheavy dark matter through Higgs portal operators

The WIMPzilla hypothesis states that the dark matter is a super-weakly-interacting and super-heavy particle. Conventionally, the WIMPzilla abundance is set by gravitational particle production during or at the end of inflation. In this study we allow the WIMPzilla to interact directly with Standard Model fields through the Higgs portal, and we calculate the thermal production (freeze-in) of WIMPzilla dark matter from the annihilation of Higgs boson pairs in the plasma. The two particle-physics model parameters are the WIMPzilla mass and the Higgs-WIMPzilla coupling. The two cosmological parameters are the reheating temperature and the expansion rate of the universe at the end of inflation. We delineate the regions of parameters space where either gravitational or thermal production is dominant, and within those regions we identify the parameters that predict the observed dark matter relic abundance. Allowing for thermal production opens up the parameter space, even for Planck-suppressed Higgs-WIMPzilla interactions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Percutaneous Endovascular Radiofrequency Ablation for Malignant Portal Obstruction: An Initial Clinical Experience

PurposeThe Habib™ VesOpen Catheter is a new endovascular radiofrequency ablation (RFA) device used to treat malignant portal obstruction. The purpose of this study was to evaluate the clinical feasibility and safety of RFA with this device.MethodsWe collected the clinical records and follow-up data of patients with malignant portal obstruction treated with percutaneous endovascular portal RFA using the Habib™ VesOpen Catheter. Procedure-related complications, improvement of symptoms, portal patency, survival, and postoperative biochemical tests were investigated.ResultsThe 31 patients enrolled in the study underwent 41 successful endovascular portal RFA procedures. Patients were divided into a portal-stenting (PS) group (n = 13), which underwent subsequent portal stenting with self-expandable metallic stents, and a non-stenting (NS) group (n = 18), which did not undergo stenting. No procedure-related abdominal hemorrhage or portal rupture occurred. Postablation complications included abdominal pain (n = 26), fever (n = 13), and pleural effusion (n = 15). Improvements in clinical manifestations were observed in 27 of the 31 patients. Of the 17 patients experiencing portal restenosis, 10 underwent successful repeat RFA. The rate of successful repeat RFA was significantly higher in the NS group than in the PS group. Median portal patency was shorter in the PS group than in the NS group. No mortality occurred during the 4 weeks after percutaneous endovascular portal RFA.ConclusionsPercutaneous endovascular portal RFA is a feasible and safe therapeutic option for malignant portal obstruction. Prospective investigations should be performed to evaluate clinical efficacy, in particular, the need to evaluate the necessity for subsequent portal stenting.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Portals Reference Implementation v. 1.0

The Portals reference implementation is based on the Portals 4.X API, published by Sandia National Laboratories as a freely available public document. It is designed to be an implementation of the Portals Networking Application Programming Interface and is used by several other upper layer protocols like SHMEM, GASNet and MPI. It is implemented over existing networks, specifically Ethernet and InfiniBand networks. This implementation provides Portals networks functionality and serves as a software emulation of Portals compliant networking hardware. It can be used to develop software using the Portals API prior to the debut of Portals networking hardware, such as Bull’s BXI interconnect, as well as a substitute for portals hardware on development platforms that do not have Portals compliant hardware. The reference implementation provides new capabilities beyond that of a typical network, namely the ability to have messages matched in hardware in a way compatible with upper layer software such as MPI or SHMEM. It also offers methods of offloading network operations via triggered operations, which can be used to create offloaded collective operations. Specific details on the Portals API can be found at http://portals4.org.

Grant, RyanE.↗