density correction
Recently Published Documents


TOTAL DOCUMENTS

82
(FIVE YEARS 12)

H-INDEX

17
(FIVE YEARS 2)

2021 ◽  
Vol 7 (4) ◽  
pp. 19-28
Author(s):  
Melton D. Parham ◽  
Salahuddin Ahmad ◽  
Hosang Jin

Abstract Purpose To investigate dosimetric implications of biodegradable Biozorb (BZ) markers for proton accelerated partial breast irradiation (APBI) plans. Materials and Methods Six different BZs were placed within in-house breast phantoms to acquire computed tomography (CT) images. A contour correction method with proper mass density overriding for BZ titanium clip and surrounding tissue was applied to minimize inaccuracies found in the CT images in the RayStation planning system. Each breast phantom was irradiated by a monoenergetic proton beam (103.23 MeV and 8×8 cm2) using a pencil-beam scanning proton therapy system. For a range perturbation study, doses were measured at 5 depths below the breast phantoms by using an ionization chamber and compared to the RayStation calculations with 3 scenarios for the clip density: the density correction method (S1: 1.6 g/cm3), raw CT (S2), and titanium density (S3: 4.54 g/cm3). For the local dose perturbation study, the radiographic EDR2 film was placed at 0 and 2 cm below the phantoms and compared to the RayStation calculations. Clinical effects of the perturbations were retrospectively examined with 10 APBI plans for the 3 scenarios (approved by our institutional review board). Results In the range perturbation study, the S1 simulation showed a good agreement with the chamber measurements, while excess pullbacks of 1∼2 mm were found in the S2 and S3 simulations. The film study showed local dose shadowing and perturbation by the clips that RayStation could not predict. In the plan study, no significant differences in the plan quality were found among the 3 scenarios. However, substantial range pullbacks were observed for S3. Conclusion The density correction method could minimize the dose and range difference between measurement and RayStation prediction. It should be avoided to simply override the known physical density of the BZ clips for treatment planning owing to overestimation of the range pullback.


ACTA IMEKO ◽  
2020 ◽  
Vol 9 (5) ◽  
pp. 33
Author(s):  
M. L. Win ◽  
T. Sanponpute ◽  
B. Suktat

There are four major uncertainty components to be considered when performing mass comparisons. They are uncertainties of weighing process, reference weight used, air buoyancy, and mass comparator. The systematic effect of air buoyancy can be greatly reduced if the air density and the densities of the test and reference weights are known. This paper will emphasis on the uncertainty due to air buoyancy correction only. To calculate the uncertainty of air density correction, partial derivatives of temperature, barometric pressure and humidity must be performed. In this paper, two methods for partial differentiation of air density components are discussed.


2020 ◽  
pp. 20200239
Author(s):  
Chen Su ◽  
Hiroyuki Okamoto ◽  
Shie Nishioka ◽  
Tatsuya Sakasai ◽  
Daisuke Fujiyama ◽  
...  

Objective: This study aimed to assess the dosimetric effect of intestinal gas of stereotactic magnetic resonance (MR)-guided adaptive radiation therapy (SMART) on target and critical organs for pancreatic cancer without on-line electron density correction (EDC). Methods: Thirty pancreatic cancer patients who underwent on-line SMART were selected for this study. The treatment time of each stage and the total treatment time were recorded and analyzed. The concerned dose-volume parameters of target and organs at risk (OAR) were compared with and without an intestinal gas EDC using the Wilcoxon signed rank test. Analysis items with p value < 0.05 were considered statistically significant. The relationships between dosimetric difference and intestinal gas volume variation were investigated using the Spearman test. Results: The average treatment time was 82 min, and the average EDC time was 8 min, which accounted for 10% of the overall treatment time. There were no significant differences in CTV (GTV), PTV, bowel, stomach, duodenum, and skin (p > 0.05) with respect to dose volume parameters. For the Dmax of gastrointestinal organs (p = 0.03), the mean dose of the liver (p = 0.002) and kidneys (p = 0.03 and p = 0.04 for the left and right kidneys, respectively), there may be a risk of slight overestimation compared with EDC, and for the Dmax of the spinal cord (p = 0.02), there may be a risk of slight underestimation compared with EDC. A weak correlation for D95 in the PTV and D0.5 cc in the duodenum was observed. Conclusion: For patients with similar inter fractional intestinal gas distribution, EDC had little dosimetric effects on the D0.5 cc of all GI organs and dose volume parameters of target in most plans. Advances in knowledge: By omitting the EDC of intestinal gas, the online SMART treatment time can be shortened.


Processes ◽  
2020 ◽  
Vol 8 (8) ◽  
pp. 997
Author(s):  
Yilin Deng ◽  
Jian Feng ◽  
Fulai Wan ◽  
Xi Shen ◽  
Bin Xu

The aim of this paper is to investigate the influence of different turbulence models (k−ε, RNG k−ε, and SST k−ω) on the numerical simulation of cavitating flow in thermosensitive fluid. The filter-based model and density correction method were employed to correct the turbulent viscosity of the three turbulence models. Numerical results obtained were compared to experimental ones which were conducted on the NACA0015 hydrofoil at different temperatures. The applicability of the numerical solutions of different turbulence model was studied in detail. The modified RNG k−ε model has higher accuracy in the calculation of cavitating flow at different temperatures.


2020 ◽  
Author(s):  
Julia Brosch ◽  
Carlos Uribe ◽  
Astrid Gosewisch ◽  
Lena Kaiser ◽  
Andrei Todica ◽  
...  

Abstract Background Patients with metastatic, castration-resistant prostate cancer (mCRPC) present with an increased tumor burden in the skeleton. For these patients, Lutetium-177 (Lu-177) radioligand therapy targeting the prostate-specific membrane antigen (PSMA) has gained increasing interest with promising outcome data. Patient-individualized dosimetry enables quantification of therapy success with the aim of minimizing absorbed dose to organs at risk while maximizing absorbed dose to tumors. Different dosimetric approaches with varying complexity and accuracy exist for this purpose. The relatively simple OLINDA method applied to tumors assumes a homogeneous activity distribution in a sphere with unit density. Voxel S value (VSV) approaches can account for heterogeneous activities but are simulated for a specific tissue. Full patient-individual Monte Carlo (MC) dose simulation addresses both, heterogeneous activity and density distributions. Subsequent CT-based density correction has the potential to overcome the assumption of homogeneous density in OLINDA and VSV methods, which could be a major limitation for the application in bone metastases with heterogeneous density. The aim of this investigation is a comparison of these methods for bone lesion dosimetry in mCRPC patients receiving Lu-177-PSMA therapy. Results In total, 289 bone lesions in 15 mCRPC patients were analyzed. Percentage deviation (PD) of absorbed lesion doses compared to full MC was + 7 ± 13% (min: -60%; max: +47%) for the OLINDA unit density sphere model. With an applied CT-based density weighting to account for density differences in bone lesions, PD was − 15 ± 6% (min: -54%; max: -2%). For a soft tissue VSV approach, large PDs of + 16 ± 13% (min: -56%; max: +57%) were found; after voxel-wise density correction this was reduced to -5 ± 2% (min: -15%; max: -2%). The use of a combination of standard soft tissue and cortical bone VSVs showed deviations of -35 ± 8% (min: -76%; max: +5%). With additional voxel-wise density weighting, the PD was − 3 ± 2% (min: -13%; max: 0%). Conclusion Based on our bone lesion dosimetry results, a VSV approach with subsequent CT-based, voxel-wise density correction enabled dose estimates, that closely replicate computationally-demanding gold-standard full MC dose simulations.


2020 ◽  
Vol 125 (7) ◽  
pp. 625-635 ◽  
Author(s):  
Alessandra Farchione ◽  
Anna Rita Larici ◽  
Carlotta Masciocchi ◽  
Giuseppe Cicchetti ◽  
Maria Teresa Congedo ◽  
...  

2019 ◽  
Author(s):  
Xuan Cheng ◽  
Junfeng Yang ◽  
Cunying Xiao ◽  
Xiong Hu

Abstract. This paper describes the density correction of the NRLMSISE-00 using more than 15 years (2002–2016) of TIMED/SABER satellite atmospheric density data from the middle atmosphere (20–100 km). A bias correction factor dataset is established based on the density differences between the TIMED/SABER data and NRLMSISE-00. Seven height nodes are set in the range 20–100 km. The different scale oscillations of the correction factor are separated at each height node, and the spherical harmonic function is used to fit the coefficients of the different timescale oscillations to obtain a spatiotemporal function at each height node. Cubic spline interpolation is used to obtain the correction factor at other heights. The spatiotemporal correction function proposed in this paper achieves a good correction effect on the atmospheric density of the NRLMSISE-00 model. The correction effect becomes more pronounced as the height increases. After correction, the relative error of the model decreased by 40–50 % in July, especially at ±40° N in the 80–100 km region. The atmospheric model corrected by the spatiotemporal function achieves higher accuracy for forecasting the atmospheric density during different geomagnetic activities. During geomagnetic storms, the relative errors in atmospheric density at 100 km, 72 km, and 32 km decrease from 41.21 %, 28.56 %, and 3.03 % to −9.65 %, 5.38 %, and 1.44 %, respectively, after correction. The relative errors in atmospheric density at 100 km, 72 km, and 32 km decrease from 68.95 %, 24.98 %, and 3.56 % to 3.49 %, 3.02 %, and 1.77 %, respectively, during geomagnetic quiet period. The correction effect during geomagnetic quiet period is better than that during geomagnetic storms at a height of 100 km. The subsequent effects of geomagnetic activity will be considered, and the atmospheric density during magnetic storms and quiet periods is corrected separately near 100 km. The ability of the model to characterize the mid-atmosphere (20–100 km) is significantly improved compared with the pre-correction performance. As a result, the corrected NRLMSISE-00 can provide more reliable atmospheric density data for scientific research and engineering fields such as data analysis, instrument design, and aerospace vehicles.


2019 ◽  
Vol 56 (5) ◽  
pp. 493-503 ◽  
Author(s):  
Peter Tschirhart ◽  
William A. Morris ◽  
John Mims ◽  
Hernan Ugalde

The influence of topography on gravity and gravity gradiometry measurements is profound and should be minimized prior to geological interpretation. The standard way of minimizing these effects is through the computation of a terrain correction. Terrain corrections require two inputs: topography and density. Often, geology and topography are inextricably intertwined: topography is caused by a change in geology. In geologic environments where there is a structural and (or) stratigraphic control on the near-surface mass distribution, using a single density value in the corrections leads to removal of the topographic effect of rocks having the chosen density. Any remaining gravity signal that correlates with topography is providing geological information. If the objective is to produce a gravity map with minimal topographic signal, then a regionally variable density correction is a means of compensating for this effect. In this paper, we demonstrate how to apply a spatially variable density correction using ground gravity and airborne gravity gradiometry data for the geologically complex Bathurst Mining Camp, northern New Brunswick, Canada. Ground gravity and airborne full tensor gravity gradiometry measurements are subdivided into a series of domains on the basis of the underlying tectonostratigraphic group. Terrain and Bouguer corrections are calculated for each domain using representative density values obtained from drill core and surface sampling throughout the Bathurst Mining Camp. The output from the spatially variable density correction is then compared with previous maps. Overall, the differences are subtle, but the spatially variably density allows for isolated anomalies to be better resolved.


Sign in / Sign up

Export Citation Format

Share Document