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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Is Dose Deformation–Invariance Hypothesis Verified in Prostate IGRT?

Purpose: To assess dose uncertainties resulting from the dose deformation–invariance hypothesis in prostate cone beam computed tomography (CT)–based image guided radiation therapy (IGRT), namely to evaluate whether rigidly propagated planned dose distribution enables good estimation of fraction dose distributions. Methods and Materials: Twenty patients underwent a CT scan for planning intensity modulated radiation therapy–IGRT delivering 80 Gy to the prostate, followed by weekly CT scans. Two methods were used to obtain the dose distributions on the weekly CT scans: (1) recalculating the dose using the original treatment plan; and (2) rigidly propagating the planned dose distribution. The cumulative doses were then estimated in the organs at risk for each dose distribution by deformable image registration. The differences between recalculated and propagated doses were finally calculated for the fraction and the cumulative dose distributions, by use of per-voxel and dose-volume histogram (DVH) metrics. Results: For the fraction dose, the mean per-voxel absolute dose difference was <1 Gy for 98% and 95% of the fractions for the rectum and bladder, respectively. The maximum dose difference within 1 voxel reached, however, 7.4 Gy in the bladder and 8.0 Gy in the rectum. The mean dose differences were correlated with gas volume for the rectum and patient external contour variations for the bladder. The mean absolute differences for the considered volume receiving greater than or equal to dose x (V{sub x}) of the DVH were between 0.37% and 0.70% for the rectum and between 0.53% and 1.22% for the bladder. For the cumulative dose, the mean differences in the DVH were between 0.23% and 1.11% for the rectum and between 0.55% and 1.66% for the bladder. The largest dose difference was 6.86%, for bladder V{sub 80Gy}. The mean dose differences were <1.1 Gy for the rectum and <1 Gy for the bladder. Conclusions: The deformation–invariance hypothesis was corroborated for the organs at risk in prostate IGRT except in cases of a large disappearance or appearance of rectal gas for the rectum and large external contour variations for the bladder.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Predictors of Liver Toxicity Following Stereotactic Body Radiation Therapy for Hepatocellular Carcinoma

Purpose: To identify risk factors associated with a decline in liver function after stereotactic body radiation therapy (SBRT) for hepatocellular carcinoma. Methods and Materials: Data were analyzed from patients with hepatocellular carcinoma treated on clinical trials of 6-fraction SBRT. Liver toxicity was defined as an increase in Child-Pugh (CP) score ≥2 three months after SBRT. Clinical factors, SBRT details, and liver dose-volume histogram (DVH) parameters were tested for association with toxicity using logistic regression. CP class B patients were analyzed separately. Results: Among CP class A patients, 101 were evaluable, with a baseline score of A5 (72%) or A6 (28%). Fifty-three percent had portal vein thrombus. The median liver volume was 1286 cc (range, 766-3967 cc), and the median prescribed dose was 36 Gy (range, 27-54 Gy). Toxicity was seen in 26 patients (26%). Thrombus, baseline CP of A6, and lower platelet count were associated with toxicity on univariate analysis, as were several liver DVH-based parameters. Absolute and spared liver volumes were not significant. On multivariate analysis for CP class A patients, significant associations were found for baseline CP score of A6 (odds ratio [OR], 4.85), lower platelet count (OR, 0.90; median, 108 × 10{sup 9}/L vs 150 × 10{sup 9}/L), higher mean liver dose (OR, 1.33; median, 16.9 Gy vs 14.7 Gy), and higher dose to 800 cc of liver (OR, 1.11; median, 14.3 Gy vs 6.0 Gy). With 13 CP-B7 patients included or when dose to 800 cc of liver was replaced with other DVH parameters (eg, dose to 700 or 900 cc of liver) in the multivariate analysis, effective volume and portal vein thrombus were associated with an increased risk. Conclusions: Baseline CP scores and higher liver doses (eg, mean dose, effective volume, doses to 700-900 cc) were strongly associated with liver function decline 3 months after SBRT. A lower baseline platelet count and portal vein thrombus were also associated with an increased risk.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Predicting Patient-specific Dosimetric Benefits of Proton Therapy for Skull-base Tumors Using a Geometric Knowledge-based Method

Purpose: To predict the organ at risk (OAR) dose levels achievable with proton beam therapy (PBT), solely based on the geometric arrangement of the target volume in relation to the OARs. A comparison with an alternative therapy yields a prediction of the patient-specific benefits offered by PBT. This could enable physicians at hospitals without proton capabilities to make a better-informed referral decision or aid patient selection in model-based clinical trials. Methods and Materials: Skull-base tumors were chosen to test the method, owing to their geometric complexity and multitude of nearby OARs. By exploiting the correlations between the dose and distance-to-target in existing PBT plans, the models were independently trained for 6 types of OARs: brainstem, cochlea, optic chiasm, optic nerve, parotid gland, and spinal cord. Once trained, the models could estimate the feasible dose–volume histogram and generalized equivalent uniform dose (gEUD) for OAR structures of new patients. The models were trained using 20 patients and validated using an additional 21 patients. Validation was achieved by comparing the predicted gEUD to that of the actual PBT plan. Results: The predicted and planned gEUD were in good agreement. Considering all OARs, the prediction error was +1.4 ± 5.1 Gy (mean ± standard deviation), and Pearson's correlation coefficient was 93%. By comparing with an intensity modulated photon treatment plan, the model could classify whether an OAR structure would experience a gain, with a sensitivity of 93% (95% confidence interval: 87%-97%) and specificity of 63% (95% confidence interval: 38%-84%). Conclusions: We trained and validated models that could quickly and accurately predict the patient-specific benefits of PBT for skull-base tumors. Similar models could be developed for other tumor sites. Such models will be useful when an estimation of the feasible benefits of PBT is desired but the experience and/or resources required for treatment planning are unavailable.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

Early Assessment of Treatment Responses During Radiation Therapy for Lung Cancer Using Quantitative Analysis of Daily Computed Tomography

Purpose: To investigate early tumor and normal tissue responses during the course of radiation therapy (RT) for lung cancer using quantitative analysis of daily computed tomography (CT) scans. Methods and Materials: Daily diagnostic-quality CT scans acquired using CT-on-rails during CT-guided RT for 20 lung cancer patients were quantitatively analyzed. On each daily CT set, the contours of the gross tumor volume (GTV) and lungs were generated and the radiation dose delivered was reconstructed. The changes in CT image intensity (Hounsfield unit [HU]) features in the GTV and the multiple normal lung tissue shells around the GTV were extracted from the daily CT scans. The associations between the changes in the mean HUs, GTV, accumulated dose during RT delivery, and patient survival rate were analyzed. Results: During the RT course, radiation can induce substantial changes in the HU histogram features on the daily CT scans, with reductions in the GTV mean HUs (dH) observed in the range of 11 to 48 HU (median 30). The dH is statistically related to the accumulated GTV dose (R{sup 2} > 0.99) and correlates weakly with the change in GTV (R{sup 2} = 0.3481). Statistically significant increases in patient survival rates (P=.038) were observed for patients with a higher dH in the GTV. In the normal lung, the 4 regions proximal to the GTV showed statistically significant (P<.001) HU reductions from the first to last fraction. Conclusion: Quantitative analysis of the daily CT scans indicated that the mean HUs in lung tumor and surrounding normal tissue were reduced during RT delivery. This reduction was observed in the early phase of the treatment, is patient specific, and correlated with the delivered dose. A larger HU reduction in the GTV correlated significantly with greater patient survival. The changes in daily CT features, such as the mean HU, can be used for early assessment of the radiation response during RT delivery for lung cancer.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

MR-OPERA: A Multicenter/Multivendor Validation of Magnetic Resonance Imaging–Only Prostate Treatment Planning Using Synthetic Computed Tomography Images

Purpose: To validate the dosimetric accuracy and clinical robustness of a commercially available software for magnetic resonance (MR) to synthetic computed tomography (sCT) conversion, in an MR imaging–only workflow for 170 prostate cancer patients. Methods and Materials: The 4 participating centers had MriPlanner (Spectronic Medical), an atlas-based sCT generation software, installed as a cloud-based service. A T2-weighted MR sequence, covering the body contour, was added to the clinical protocol. The MR images were sent from the MR scanner workstation to the MriPlanner platform. The sCT was automatically returned to the treatment planning system. Four MR scanners and 2 magnetic field strengths were included in the study. For each patient, a CT-treatment plan was created and approved according to clinical practice. The sCT was rigidly registered to the CT, and the clinical treatment plan was recalculated on the sCT. The dose distributions from the CT plan and the sCT plan were compared according to a set of dose-volume histogram parameters and gamma evaluation. Treatment techniques included volumetric modulated arc therapy, intensity modulated radiation therapy, and conventional treatment using 2 treatment planning systems and different dose calculation algorithms. Results: The overall (multicenter/multivendor) mean dose differences between sCT and CT dose distributions were below 0.3% for all evaluated organs and targets. Gamma evaluation showed a mean pass rate of 99.12% (0.63%, 1 SD) in the complete body volume and 99.97% (0.13%, 1 SD) in the planning target volume using a 2%/2-mm global gamma criteria. Conclusions: Results of the study show that the sCT conversion method can be used clinically, with minimal differences between sCT and CT dose distributions for target and relevant organs at risk. The small differences seen are consistent between centers, indicating that an MR imaging–only workflow using MriPlanner is robust for a variety of field strengths, vendors, and treatment techniques.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Dose Prediction Model for Duodenum Sparing With a Biodegradable Hydrogel Spacer for Pancreatic Cancer Radiation Therapy

We previously have shown the feasibility of duodenum sparing using a biodegradable hydrogel spacer in pancreatic cancer radiation therapy. In this study, we propose an overlap volume histogram (OVH) prediction model to select patients who might benefit from hydrogel placement and to predict the hydrogel spacing required to achieve clinical constraints.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

A Systematic Post-QUANTEC Review of Tolerance Doses for Late Toxicity After Prostate Cancer Radiation Therapy

The aims of this study were to systematically review tolerance doses for late distinct gastrointestinal (GI), genitourinary (GU), and sexual dysfunction (SD) symptoms after external beam radiation therapy (EBRT) alone and treatments involving brachytherapy (BT) for prostate cancer after Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) and ultimately to perform quantitative syntheses of identified dose/volume tolerances represented by dose-volume histogram (DVH) thresholds, that is, statistically significant (P ≤ .05) cutoff points between symptomatic and asymptomatic patients in a certain study.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Dose Summation Strategies for External Beam Radiation Therapy and Brachytherapy in Gynecologic Malignancy: A Review from the NRG Oncology and NCTN Medical Physics Subcommittees

Definitive, nonsurgical management of gynecologic malignancies involves external beam radiation therapy (EBRT) and/or brachytherapy (BT). Summation of the cumulative dose is critical to assess the total biologic effective dose to targets and organs at risk. Cumulative dose calculation from EBRT and BT can be performed with or without image registration (IR) and biologic dose summation. Among these dose summation strategies, linear addition of dose-volume histogram (DVH) parameters without IR is the global standard for composite dose reporting. This approach stems from an era without image guidance and simple external beam and brachytherapy treatment approaches. With technological advances, EBRT and high-dose-rate BT have evolved to allow for volume-based treatment planning and delivery. Modern conformal therapeutic radiation involves volumetric or intensity modulated EBRT, capable of simultaneously treating multiple targets at different specified dose levels. Therefore, given the complexity of modern radiation treatment, the linear addition of DVH parameters from EBRT and high-dose-rate BT is challenging to represent the combined dose distribution. Deformable image registration (DIR) between EBRT and image guided brachytherapy (IGBT) data sets may provide a more nuanced calculation of multimodal dose accumulation. However, DIR is still nascent in this regard, and needs further development for accuracy and efficiency for clinical use. Biologic dose summation can combine physical dose maps from EBRT and each IGBT fraction, thereby generating a composite DVH from the biologic effective dose. However, accurate radiobiologic parameters are tissue-dependent and not well characterized. A combination of voxel-based DIR and biologic weighted dose maps may be the best approximation of dose accumulation but remains invalidated. The purpose of this report is to review dose summation strategies for EBRT and BT, including conventional equivalent dose in 2-Gy fractions dose summation without image registration, physical dose summation using 3-dimensional rigid IR and DIR, and biologic dose summation. We also provide general clinical workflows for IGBT with a focus on cervical cancer.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2020

An Electron Backscatter Diffraction Analysis of Grain Boundary Initiated Discontinuous Precipitation in U-10Mo

The effect of varied thermomechanical processing on discontinuous precipitation (DP) in U-10Mo was investigated, with specific emphasis on understanding the role of grain boundary misorientation in DP. Varied prior homogenization heat treatment and thermomechanical processing resulted in differences in both the fraction of DP and the colony width, and was attributed to variations in the grain boundary misorientation distribution. Regardless of the degree of DP-based transformation, extensive growth of DP colonies was dominant on 30°–45° misorientation boundaries. Interestingly, misorientation histograms of the deformed and annealed specimens suggest the processing steps involved may have inhibited DP colony growth along a small fraction of these high angle boundaries. Large-area electron backscatter diffraction montages coupled with high resolution mapping suggest symmetric {110}-type interfaces may be important considerations for mitigating extensive DP growth in this alloy system.

Discontinuous Precipitation, Uranium, Electron Bac↗
DOE OSTI2021

Uranium Oxide Synthetic Pathway Discernment through Unsupervised Morphological Analysis

We present a novel unsupervised machine learning method for quantitative representation of scanning electron micrographs and its applications and performance for nuclear forensic analysis of uranium ore concentrates. The method uses a vector quantizing variational autoencoder followed by a histogram operation to encode a micrograph into a single dimensional representation, called the latent vector. The method requires no extant labeling of the data and can be applied over large datasets of micrographs with minimal human interaction. The representations generated are broadly descriptive of each micrograph and the microstructure of the material imaged. In the case of uranium ore concentrate analysis, the representations were amenable to processing reagent and ore concentrate species classification with accuracy of 81:8%, which is competitive with state-of-the-art supervised networks. The representations were also used to classify previously unseen processing routes, were able to classify imaging parameters such as magnification (to 76:0% accuracy), were able to classify fine grained process parameters such as calcining temperature (to 74:4% accuracy), and their informatic properties indicate that they are generally descriptive of the image represented. This method can be applied across microstructure analysis fields to perform quantitative analysis without the need for labor intensive and possibly biased human analysis.

Scanning Electron Microscopy, Vector Quantizing Va↗
DOE OSTI2025

Prediction of electric and magnetic fields from spectral data using machine learning algorithms for Doppler-free saturation spectroscopy diagnostics

The prediction of electric and magnetic field amplitudes from atomic spectral data is critical for plasma control in fusion devices such as tokamaks. Conventional approaches that rely on physics-based models are computationally expensive and unsuitable for real-time applications. In this work, we develop and benchmark three machine learning algorithms—simulation-based inference (SBI), fully connected neural networks (FCNN), and histogram-based gradient boosting regression (GBR-Hist)—to infer field intensities directly from Doppler-free saturation spectroscopy (DFSS) spectra. Synthetic datasets of spectra were generated using the EZSSS code and evaluated both with and without added Poisson noise to mimic experimental conditions. We find that SBI achieves the highest accuracy and robustness, FCNN provides a strong balance of accuracy and computational efficiency for real-time applications, and GBR-Hist offers the fastest inference but is more sensitive to noise. Furthermore, these results demonstrate the potential of machine learning to accelerate DFSS analysis and enhance its utility for plasma diagnostics and control.

Doppler-free saturation spectroscopy↗
DOE OSTI2016

Microstructural evolution and grain growth kinetics of GZ31 magnesium alloy

Grain growth behavior of Mg–3Gd–1Zn (GZ31) magnesium alloy was studied in a wide range of annealing time and temperature to clarify the kinetics of grain growth, microstructural evolution and related metallurgical phenomena. This material exhibited typical normal grain growth mode under annealing conditions with annealing temperature of lower than 300 °C and soaking time of lower than 240 min. However, the abnormality in grain growth was also evident at annealing temperature of 400 °C and 500 °C. The dependence of abnormal grain growth (AGG) at mentioned annealing temperatures upon microstructural features such as dispersed precipitates, which were rich in Zn and Gd, was investigated by optical micrographs, X-ray diffraction patterns, scanning electron microscopy images, and energy dispersive X-ray analysis spectra. The bimodality in grain-size distribution histograms also signified the occurrence of AGG. Based on the experimental data on grain growth obtained by annealing treatments, the grain growth exponent and the activation energy were also figured out.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Gaussian kernel density functions for compositional quantification in atom probe tomography

Highlights: • A methodology for compositional quantification from atom probe tomography is proposed. • A probability density function p(x) given discrete data points is constructed. • Each atom approximated by a Gaussian function with a particular smoothing parameter. • Density Kernel functions are used to find the optimum smoothing parameter. • The method is validated by using simulated data of semiconductor materials. - Abstract: Atom probe tomography (APT) has the ability to identify the nature and position of single atoms in a material with an almost 3D atomic resolution. However, the quantification of the material composition requires an appropriate treatment of the discrete APT data. When the amount of atoms selected to quantify the composition is relatively small, the spatial resolution is enhanced but the statistical error worsens. Conversely, the increase in the number of atoms considered reduces the spatial resolution, but improving the statistics. We have developed a methodology to reach an optimum equilibrium between the positional and the statistical error in an unsupervised form using Gaussian Kernel density functions. The validity of the method has been tested using APT simulated data of semiconductor materials. It has been proved that the chemical quantification in these materials requires the appropriate selection of the smoothing parameter, obtained without user intervention. In addition, the results have been compared to the usual techniques for composition measurement from APT data (voxelization and proximity histograms), showing better precision for high spatial resolution. This work supplies a data driven methodology based in Gaussian Kernel density functions for the accurate quantification of the composition from APT data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Clinical and dosimetric implications of intensity-modulated radiotherapy for early-stage glottic carcinoma

Conventional parallel-opposed radiotherapy (PORT) is the established standard technique for early-stage glottic carcinoma. However, case reports have reported the utility of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) with or without image guidance (image-guided radiotherapy, IGRT) in select patients. The proposed advantages of IMRT/VMAT include sparing of the carotid artery, thyroid gland, and the remaining functional larynx, although these benefits remain unclear. The following case study presents a patient with multiple vascular comorbidities treated with VMAT for early-stage glottic carcinoma. A detailed explanation of the corresponding treatment details, dose-volume histogram (DVH) analysis, and a review of the relevant literature are provided. Conventional PORT remains the standard of care for early-stage glottic carcinoma. IMRT or VMAT may be beneficial for select patients, although great care is necessary to avoid a geographical miss. Clinical data supporting the benefit of CRT are lacking. Therefore, these techniques should be used with caution and only in selected patients.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Using individual patient anatomy to predict protocol compliance for prostate intensity-modulated radiotherapy

If a prostate intensity-modulated radiation therapy (IMRT) or volumetric-modulated arc therapy (VMAT) plan has protocol violations, it is often a challenge knowing whether this is due to unfavorable anatomy or suboptimal planning. This study aimed to create a model to predict protocol violations based on patient anatomical variables and their potential relationship to target and organ at risk (OAR) end points in the setting of definitive, dose-escalated IMRT/VMAT prostate planning. Radiotherapy plans from 200 consecutive patients treated with definitive radiation for prostate cancer using IMRT or VMAT were analyzed. The first 100 patient plans (hypothesis-generating cohort) were examined to identify anatomical variables that predict for dosimetric outcome, in particular OAR end points. Variables that scored significance were further assessed for their ability to predict protocol violations using a Classification and Regression Tree (CART) analysis. These results were then validated in a second group of 100 patients (validation cohort). In the initial analysis of the hypothesis-generating cohort, percentage of rectum overlap in the planning target volume (PTV) (%OR) and percentage of bladder overlap in the PTV (%OB) were highlighted as significant predictors of rectal and bladder dosimetry. Lymph node treatment was also significant for bladder outcomes. For the validation cohort, CART analysis showed that %OR of < 6%, 6% to 9% and > 9% predicted a 13%, 63%, and 100% rate of rectal protocol violations respectively. For the bladder, %OB of < 9% vs > 9% is associated with 13% vs 88% rate of bladder constraint violations when lymph nodes were not treated. If nodal irradiation was delivered, plans with a %OB of < 9% had a 59% risk of violations. Percentage of rectum and bladder within the PTV can be used to identify individual plan potential to achieve dose-volume histogram (DVH) constraints. A model based on these factors could be used to reduce planning time, improve work flow, and strengthen plan quality and consistency.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2016

Pancreatic cancer planning: Complex conformal vs modulated therapies

To compare the roles of intensity-modulated radiation therapy (IMRT) and volumetric- modulated arc therapy (VMAT) therapy as compared to simple and complex 3-dimensional chemoradiotherpy (3DCRT) planning for resectable and borderline resectable pancreatic cancer. In all, 12 patients who received postoperative radiotherapy (8) or neoadjuvant concurrent chemoradiotherapy (4) were evaluated retrospectively. Radiotherapy planning was performed for 4 treatment techniques: simple 4-field box, complex 5-field 3DCRT, 5 to 6-field IMRT, and single-arc VMAT. All volumes were approved by a single observer in accordance with Radiation Therapy Oncology Group (RTOG) Pancreas Contouring Atlas. Plans included tumor/tumor bed and regional lymph nodes to 45 Gy; with tumor/tumor bed boosted to 50.4 Gy, at least 95% of planning target volume (PTV) received the prescription dose. Dose-volume histograms (DVH) for multiple end points, treatment planning, and delivery time were assessed. Complex 3DCRT, IMRT, and VMAT plans significantly (p < 0.05) decreased mean kidney dose, mean liver dose, liver (V{sub 30}, V{sub 35}), stomach (D{sub 10}%), stomach (V{sub 45}), mean right kidney dose, and right kidney (V{sub 15}) as compared with the simple 4-field plans that are most commonly reported in the literature. IMRT plans resulted in decreased mean liver dose, liver (V{sub 35}), and left kidney (V{sub 15}, V{sub 18}, V{sub 20}). VMAT plans decreased small bowel (D{sub 10}%, D{sub 15}%), small bowel (V{sub 35}, V{sub 45}), stomach (D{sub 10}%, D{sub 15}%), stomach (V{sub 35}, V{sub 45}), mean liver dose, liver (V{sub 35}), left kidney (V{sub 15}, V{sub 18}, V{sub 20}), and right kidney (V{sub 18}, V{sub 20}). VMAT plans significantly decreased small bowel (D{sub 10}%, D{sub 15}%), left kidney (V{sub 20}), and stomach (V{sub 45}) as compared with IMRT plans. Treatment planning and delivery times were most efficient for simple 4-field box and VMAT. Excluding patient setup and imaging, average treatment delivery was within 10 minutes for simple and complex 3DCRT, IMRT, and VMAT treatments. This article shows significant improvements in 3D plan performance with complex planning over the more frequently compared 3- or 4-field simple 3D planning techniques. VMAT plans continue to demonstrate potential for the most organ sparing. However, further studies are required to identify if dosimetric benefits associated with inverse optimized planning can be translated into clinical benefits and if these treatment techniques are value-added therapies for this group of patients with cancer.

61 RADIATION PROTECTION AND DOSIMETRY↗