Maximum Local Difference Research Articles

Technical note: In silico benchmarking of the linear energy transfer-based functionalities for carbon ion beams in a commercial treatment planning system.

The increasing number of studies dealing with linear energy transfer (LET)-based evaluation and optimization in the field of carbon ion radiotherapy (CIRT) indicates the rising demand for LET implementation in commercial treatment planning systems (TPS). Benchmarking studies could play a key role in detecting (and thus preventing) computation errors prior implementing such functionalities in aTPS. This in silico study was conducted to benchmark the following two LET-related functionalities in a commercial TPS against Monte Carlo simulations: (1) dose averaged LET (LETd ) scoring and (2) physical dose filtration based on LET for future LET-based treatment plan evaluation and optimization studies. The LETd scoring and LET-based dose filtering (in which the deposited dose can be separated into the dose below and above the user specified LET threshold) functionalities for carbon ions in the research version RayStation (RS) 9A-IonPG TPS (RaySearch Laboratories, Sweden) were benchmarked against GATE/Geant4 simulations. Pristine Bragg peaks (BPs) and cuboid targets, positioned at different depths in a homogeneous water phantom and a setup with heterogeneity were used for thisstudy. For all setups (homogeneous and heterogeneous), the mean absolute (and relative) LETd difference was less than 1 keV/ m (3.5%) in the plateau and target and less than 2 keV/ m (8.3%) in the fragmentation tail. The maximum local differences were 4 and 6 keV/ m, respectively. The mean absolute (and relative) physical dose differences for both low- and high-LET doses were less than 1 cGy (1.5%) in the plateau, target and tail with a maximum absolute difference of 2cGy. No computation error was found in the tested functionalities except for LETd in lateral direction outside the target, showing the limitation of the implemented monochrome model in the tested TPSversion.

Exploring the applicability of a simplified fully coupled flow/orientation algorithm developed for polymer composites extrusion deposition additive manufacturing

Abstract Prior literature employed a finite element based fully coupled algorithm that solved the flow/orientation coupling effects in extrusion deposition additive manufacturing, i.e., a key component for identifying the material properties of solidified deposited polymer composites. However, the complex iterative solution protocol reduces the computational capability of the algorithm. This paper simplifies the finite element based fully coupled algorithm by employing a scalar representation of the fourth order orientation tensor affected viscosity tensor. The revised code predicts similar fiber orientation results as compared to a related prior study. With the simplified fully coupled algorithm, effects of material deposition rate and fiber aspect ratio on a 2D planar large area extrusion deposition flow are explored, where the power law rheology model is employed for the flow simulation. Computed results show that an increased material deposition rate reduces the extrudate-swell ratio of the melt front and varies the local fiber orientation of the deposited bead especially near the flow region in contact with the substrate. Higher fiber aspect ratio enhances the principal fiber alignment of the extrusion and deposition flows, where the maximum local difference of the principal A 11 component is 23% with increasing fiber aspect ratio from 10 to 25.

An ECG Denoising Method Based on the Generative Adversarial Residual Network

High-quality and high-fidelity removal of noise in the Electrocardiogram (ECG) signal is of great significance to the auxiliary diagnosis of ECG diseases. In view of the single function of traditional denoising methods and the insufficient performance of signal details after denoising, a new method of ECG denoising based on the combination of the Generative Adversarial Network (GAN) and Residual Network is proposed. The method adopted in this paper is based on the GAN structure, and it restructures the generator and discriminator. In the generator network, residual blocks and Skip-Connecting are used to deepen the network structure and better capture the in-depth information in the ECG signal. In the discriminator network, the ResNet framework is used. In order to optimize the noise reduction process and solve the lack of local relevance considering the global ECG problem, the differential function and overall function of the maximum local difference are added in the loss function in this paper. The experimental results prove that the method used in this article has better performance than the current excellent S-Transform (S-T) algorithm, Wavelet Transform (WT) algorithm, Stacked Denoising Autoencoder (S-DAE) algorithm, and Improved Denoising Autoencoder (I-DAE) algorithm. Experiments show that the Root Mean Square Error (RMSE) of this method in the Massachusetts Institute of Technology and Beth Israel Hospital (MIT-BIH) noise pressure database is 0.0102, and the Signal-to-Noise Ratio (SNR) is 40.8526 dB, which is compared with that of the most advanced experimental methods. Our method improves the SNR by 88.57% on average. Besides the three noise intensities for comparison experiments, additional noise reduction experiments are also performed under four noise intensities in our paper. The experimental results verify the scientific nature of the model, which is that our method can effectively retain the important information conveyed by the original signal.

Evaluation of lung heterogeneity effects on dosimetric parameters in small photon fields using MAGIC polymer gel, Gafchromic film, and Monte Carlo simulation

In this work, the performance of MAGIC polymer gel in measuring dosimetric parameters beyond lung heterogeneity in small fields was investigated. All data were obtained using MAGIC, EBT2, and MC in four small field sizes. The maximum local differences between MAGIC and MC were less than 5.1, 3.9, 3.1, and 2.6% for PDD values behind lung heterogeneity at 5, 10, 20, and 30 mm field sizes, respectively. The findings showed that MAGIC is a suitable tool for dosimetry behind low-density heterogeneity.

Evaluation of MRI-based MAGIC polymer gel dosimeter in small photon fields

Background: Accurate small radiation field dosimetry is essential in modern radiotherapy techniques such as stereotactic radiosurgery (SRS) and intensity modulated radiotherapy (IMRT). Precise measurement of dosimetric parameters such as beam profile, percentage depth doses and output factor of these beams are complicated due to the electron disequilibrium and the steep dose gradients. In the present work the MAGIC polymer gel was used for dosimetry of small circular photon beams. The results of MAGIC were compared with EBT2 measurements and Monte Carlo (MC) calculations. Materials and Methods: Experimental measurements were made by mentioned dosimeters in four small field sizes 5, 10, 20 and 30 mm. The BEAMnrc code based on EGSnrc was used for simulation to calculate dosimetric parameters at these small fields. The phantoms were irradiated in a 6 MV photon beam Varian 2100C linear accelerator at SSD=100 cm. gel readout performed by 3 Tesla MRI scanner. Results: The results showed that the Percent depth dose (PDD) values measured and calculated by EBT2 film and MC had maximum local differences 4% and 5% with PDD values measured by MAGIC for field size of 5mm respectively. These differences decreased for larger field sizes. The measurements of output factor and penumbra (80%-20%) and (90%-10%) showed good agreement between the measurements and MC calculation. Conclusion: This study showed that the MAGIC polymer gel based on high resolution MRI images is useful detector for small field dosimetry but its agreement with MC is less than agreement of EBT2 film with MC.

SU‐E‐T‐328: Dosimetric Impact of Cobalt‐Chrome Stabilization Hardware in Paraspinal Radiation Therapy

Purpose:Due to saturation, high density materials Result in an apparent density of 3.2 g/cm3 in CT images. The true density of traditional titanium stabilization rods (∼4.4 g/cm3) is typically ignored in treatment planning. This may not be acceptable for new cobalt‐chrome rods with a density of 8.5 g/cm3. This study reports the dosimetric impact of cobalt‐chrome rods in paraspinal radiotherapy.Methods:For titanium and cobalt‐chrome rods, two planning studies were done for both IMRT and VMAT in Varian Eclipse using AAA. 1) The effect of planning without assigning the true rod density was assessed by comparing plans generated with the apparent density and recalculated with the true density for titanium and cobalt‐chrome. 2) To test if TPS can compensate for high density rods during optimization. Furthermore, TPS calculation accuracy was verified using MapCheck for a single 20 × 10 cm2 field. The MapCheck was incrementally shifted to achieve measurement resolution of 1 mm.Results:PTV coverage was ∼0.3% and ∼4.7% lower in plans that were recalculated with the true rod density of titanium and cobalt‐chrome, respectively. PTV coverage can be maintained if the correct density is used in optimization. Measurements showed that TPS overestimated the dose locally by up to 11% for cobalt‐chrome rods and up to 4% for titanium rods if the density is incorrect. With density corrected, maximum local differences of 6% and 3% were seen for cobalt‐chrome and titanium rods, respectively. At 2 cm beneath a rod, electrons scattered from the side of the rod increased the lateral dose and diminished as depth increases. TPS was not able to account for this effect properly even with the true rod density assigned.Conclusion:Neglecting the true density of cobalt‐chrome rods can cause under coverage to the PTV. Assigning the correct density during treatment planning can minimize unexpected decrease in PTV dose.

Steady computations of ingress through gas turbine rim seals

In gas turbines, rim seals are fitted at the periphery of the wheel-space between the turbine disc and its adjacent casing; their purpose is to reduce the ingress of hot mainstream gases. This paper describes the use of a three-dimensional, steady-state model to investigate ingress through engine-representative single and double radial-clearance seals. The three-dimensional Reynolds-averaged Navier–Stokes computations of a simplified turbine stage are carried out using the commercial computational fluid dynamics code ANSYS CFX v13, and the model is based on the geometry of an experimental test rig at the University of Bath. The measured variation of the peak-to-trough pressure difference in the annulus, which is the main driving mechanism for ingress, is reproduced well qualitatively by the computations; quantitatively, the maximum local differences between computation and experiment are less than 20% of the measured peak-to-trough circumferential variation. The radial variation of swirl ratio in the rotor–stator wheel-space is well predicted over the range of flow rates and rim seal geometries studied. The radial distribution of sealing effectiveness determined from experiments is reproduced inward of the mixing region near the seal clearance over a range of sealing flow rates; some over-prediction of the effectiveness was found for both seals at high radius, probably due to limitations in the turbulent mixing modelling. The three-dimensional steady-state approach may be a practical tool for the engine designer where there is a lack of experimental data, providing quantitative predictions of the flow structure within the rotor–stator wheel-space and qualitative predictions of the sealing effectiveness for a given rim seal geometry.

Parametrization of orographic effects on surface radiation in HIRLAM

A parametrization scheme for orographic effects on surface radiation was introduced in the High Resolution Limited Area Model. One-kilometre resolution digital elevation data were used to derive the needed orographic parameters. The scheme is applicable within a model setup of any resolution, but is shown to significantly affect the local near-surface temperatures only when the horizontal resolution is less than a few kilometres. Then, typical maximum local differences due to the new parametrizations are 50–100W m −2 in the net radiation fluxes and 1°–3° in the screen-level temperature. Interactions between clouds and radiation were detected both in the single-column and three-dimensional sensitivity experiments.

Parametrization of orographic effects on surface radiation in HIRLAM

A parametrization scheme for orographic effects on surface radiation was introduced in the High Resolution Limited Area Model. One-kilometre resolution digital elevation data were used to derive the needed orographic parameters. The scheme is applicable within a model setup of any resolution, but is shown to significantly affect the local near-surface temperatures only when the horizontal resolution is less than a few kilometres. Then, typical maximum local differences due to the new parametrizations are 50–100Wm−2 in the net radiation fluxes and 1◦–3◦ in the screen-level temperature. Interactions between clouds and radiation were detected both in the single-column and three-dimensional sensitivity experiments.

Analytic approximations for curves of growth of Doppler-Lorentz broadened lines

Closed-form expressions are derived which reproduce the exact curves of growth for Doppler-Lorentz broadened lines within a few per cent over most of the range of varibles, with maximum local differences of about 30 per cent. The results should be useful for analysis of radiative transport in non-isotropic gases since the solutions can now be carried one step further by analytic methods before resorting to numerical methods.