Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Simulation Radiological Data”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Combinatorial DNA Damage Pairing Model Based on X-Ray-Induced Foci Predicts the Dose and LET Dependence of Cell Death in Human Breast Cells

In contrast to the classic view of static DNA double-strand breaks (DSBs) being repaired at the site of damage, we hypothesize that DSBs move and merge with each other over large distances (m). As X-ray dose increases, the probability of having DSB clusters increases as does the probability of misrepair and cell death. Experimental work characterizing the X-ray dose dependence of radiation-induced foci (RIF) in nonmalignant human mammary epithelial cells (MCF10A) is used here to validate a DSB clustering model. We then use the principles of the local effect model (LEM) to predict the yield of DSBs at the submicron level. Two mechanisms for DSB clustering, namely random coalescence of DSBs versus active movement of DSBs into repair domains are compared and tested. Simulations that best predicted both RIF dose dependence and cell survival after X-ray irradiation favored the repair domain hypothesis, suggesting the nucleus is divided into an array of regularly spaced repair domains of ~;;1.55 m sides. Applying the same approach to high-linear energy transfer (LET) ion tracks, we are able to predict experimental RIF/m along tracks with an overall relative error of 12percent, for LET ranging between 30 350 keV/m and for three different ions. Finally, cell death was predicted by assuming an exponential dependence on the total number of DSBs and of all possible combinations of paired DSBs within each simulated RIF. Relative biological effectiveness (RBE) predictions for cell survival of MCF10A exposed to high-LET showed an LET dependence that matches previous experimental results for similar cell types. Overall, this work suggests that microdosimetric properties of ion tracks at the submicron level are sufficient to explain both RIF data and survival curves for any LET, similarly to the LEM assumption. Conversely, high-LET death mechanism does not have to infer linear-quadratic dose formalism as done in the LEM. In addition, the size of repair domains derived in our model are based on experimental RIF and are three times larger than the hypothetical LEM voxel used to fit survival curves. Our model is therefore an alternative to previous approaches that provides a testable biological mechanism (i.e., RIF). In addition, we propose that DSB pairing will help develop more accurate alternatives to the linear cancer risk model (LNT) currently used for regulating exposure to very low levels of ionizing radiation.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2014

Dispersion of Radionuclides and Exposure Assessment in Urban Environments: A Joint CEA and LLNL Report

In the interest of promoting the international exchange of technical expertise, the US Department of Energy’s Office of Emergency Operations (NA-40) and the French Commissariat à l'Energie Atomique et aux énergies alternatives (CEA) requested that the National Atmospheric Release Advisory Center (NARAC) of Lawrence Livermore National Laboratory (LLNL) in Livermore, California host a joint table top exercise with experts in emergency management and atmospheric transport modeling. In this table top exercise, LLNL and CEA compared each other’s flow and dispersion models. The goal of the comparison is to facilitate the exchange of knowledge, capabilities, and practices, and to demonstrate the utility of modeling dispersal at different levels of computational fidelity. Two modeling approaches were examined, a regional scale modeling approach, appropriate for simple terrain and/or very large releases, and an urban scale modeling approach, appropriate for small releases in a city environment. This report is a summary of LLNL and CEA modeling efforts from this exercise. Two different types of LLNL and CEA models were employed in the analysis: urban-scale models (Aeolus CFD at LLNL/NARAC and Parallel- Micro-SWIFT-SPRAY, PMSS, at CEA) for analysis of a 5,000 Ci radiological release and Lagrangian Particle Dispersion Models (LODI at LLNL/NARAC and PSPRAY at CEA) for analysis of a much larger (500,000 Ci) regional radiological release. Two densely-populated urban locations were chosen: Chicago with its high-rise skyline and gridded street network and Paris with its more consistent, lower building height and complex unaligned street network. Each location was considered under early summer daytime and nighttime conditions. Different levels of fidelity were chosen for each scale: (1) lower fidelity mass-consistent diagnostic, intermediate fidelity Navier-Stokes RANS models, and higher fidelity Navier-Stokes LES for urban-scale analysis, and (2) lower-fidelity single-profile meteorology versus higher-fidelity three-dimensional gridded weather forecast for regional-scale analysis. Tradeoffs between computation time and the fidelity of the results are discussed for both scales. LES, for example, requires nearly 100 times more processor time than the mass-consistent diagnostic model or the RANS model, and seems better able to capture flow entrainment behind tall buildings. As anticipated, results obtained by LLNL and CEA at regional scale around Chicago and Paris look very similar in terms of both atmospheric dispersion of the radiological release and total effective dose. Both LLNL and CEA used the same meteorological data, Lagrangian particle dispersion models, and the same dose coefficients. LLNL and CEA urban-scale modeling results show consistent phenomenological behavior and predict similar impacted areas even though the detailed 3D flow patterns differ, particularly for the Chicago cases where differences in vertical entrainment behind tall buildings are particularly notable. Although RANS and LES (LLNL) models incorporate more detailed physics than do mass-consistent diagnostic flow models (CEA), it is not possible to reach definite conclusions about the prediction fidelity of the various models as experimental measurements were not available for comparison. Stronger conclusions about the relative performances of the models involved and evaluation of the tradeoffs involved in model simplification could be made with a systematic benchmarking of urban-scale modeling. This could be the purpose of a future US / French collaborative exercise.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2012

Dynamic cone beam CT angiography of carotid and cerebral arteries using canine model

Purpose: This research is designed to develop and evaluate a flat-panel detector-based dynamic cone beam CT system for dynamic angiography imaging, which is able to provide both dynamic functional information and dynamic anatomic information from one multirevolution cone beam CT scan. Methods: A dynamic cone beam CT scan acquired projections over four revolutions within a time window of 40 s after contrast agent injection through a femoral vein to cover the entire wash-in and wash-out phases. A dynamic cone beam CT reconstruction algorithm was utilized and a novel recovery method was developed to correct the time-enhancement curve of contrast flow. From the same data set, both projection-based subtraction and reconstruction-based subtraction approaches were utilized and compared to remove the background tissues and visualize the 3D vascular structure to provide the dynamic anatomic information. Results: Through computer simulations, the new recovery algorithm for dynamic time-enhancement curves was optimized and showed excellent accuracy to recover the actual contrast flow. Canine model experiments also indicated that the recovered time-enhancement curves from dynamic cone beam CT imaging agreed well with that of an IV-digital subtraction angiography (DSA) study. The dynamic vascular structures reconstructed using both projection-based subtraction and reconstruction-based subtraction were almost identical as the differences between them were comparable to the background noise level. At the enhancement peak, all the major carotid and cerebral arteries and the Circle of Willis could be clearly observed. Conclusions: The proposed dynamic cone beam CT approach can accurately recover the actual contrast flow, and dynamic anatomic imaging can be obtained with high isotropic 3D resolution. This approach is promising for diagnosis and treatment planning of vascular diseases and strokes.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

SU-E-QI-11: Measurement of Renal Pyruvate-To-Lactate Exchange with Hyperpolarized 13C MRI

Purpose: Previous work [1] modeling the metabolic flux between hyperpolarized [1-13C]pyruvate and [1-13C]lactate in magnetic resonance spectroscopic imaging (MRSI) experiments failed to account for vascular signal artifacts. Here, we investigate a method to minimize the vascular signal and its impact on the fidelity of metabolic modeling. Methods: MRSI was simulated for renal metabolism in MATLAB both with and without bipolar gradients. The resulting data were fit to a two-site exchange model [1], and the effects of vascular partial volume artifacts on kinetic modeling were assessed. Bipolar gradients were then incorporated into a gradient echo sequence to validate the simulations experimentally. The degree of diffusion weighting (b = 32 s/mm{sup 2}) was determined empirically from 1H imaging of murine renal vascular signal. The method was then tested in vivo using MRSI with bipolar gradients following injection of hyperpolarized [1-{sup 13}C]pyruvate (∼80 mM at 20% polarization). Results: In simulations, vascular signal contaminated the renal metabolic signal at resolutions as high as 2 × 2 mm{sup 2} due to partial volume effects. The apparent exchange rate from pyruvate to lactate (k{sub p}) was underestimated in the presence of these artifacts due to contaminating pyruvate signal. Incorporation of bipolar gradients suppressed vascular signal and improved the accuracy of kp estimation. Experimentally, the in vivo results supported the ability of bipolar gradients to suppress vascular signal. The in vivo exchange rate increased, as predicted in simulations, from k{sub p} = 0.012 s-{sup 1} to k{sub p} = 0.020-{sup 1} after vascular signal suppression. Conclusion: We have demonstrated the limited accuracy of the two-site exchange model in the presence of vascular partial volume artifacts. The addition of bipolar gradients suppressed vascular signal and improved model accuracy in simulations. Bipolar gradients largely affected kp estimation in vivo. Currently, slow-flowing spins in small vessels and capillaries are only partially suppressed, so further improvement is possible. Funding support: Seed Grant from the Radiological Society of North America, GE Healthcare, University of Wisconsin Graduate School.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Land and Water Use Characteristics and Human Health Input Parameters for use in Environmental Dosimetry and Risk Assessments at the Savannah River Site. 2016 Update

Operations at the Savannah River Site (SRS) result in releases of small amounts of radioactive materials to the atmosphere and to the Savannah River. For regulatory compliance purposes, potential offsite radiological doses are estimated annually using computer models that follow U.S. Nuclear Regulatory Commission (NRC) regulatory guides. Within the regulatory guides, default values are provided for many of the dose model parameters, but the use of applicant site-specific values is encouraged. Detailed surveys of land-use and water-use parameters were conducted in 1991 and 2010. They are being updated in this report. These parameters include local characteristics of meat, milk and vegetable production; river recreational activities; and meat, milk and vegetable consumption rates, as well as other human usage parameters required in the SRS dosimetry models. In addition, the preferred elemental bioaccumulation factors and transfer factors (to be used in human health exposure calculations at SRS) are documented. The intent of this report is to establish a standardized source for these parameters that is up to date with existing data, and that is maintained via review of future-issued national references (to evaluate the need for changes as new information is released). These reviews will continue to be added to this document by revision.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2014

Experiment Design of Secondary Neutron and Charged Particles Measurement with Stopping Targets Bombarded by 100- and 230-MeV/amu Helium Ions - Paper 124

Radiotherapy using ion beams has gained momentum in radiation oncology. While the number of proton therapy facilities that have been established or are under construction is rapidly growing, interest in heavy ion (whose atomic number Z is greater than one) radiotherapy has also been revitalized in the U.S. Helium ions, with mass and charge between protons and carbon ions, have advantages of deep penetration distances with significant peak-to-entrance dose ratios and limited dose contributions from secondary neutrons and other secondary charged fragments. In consideration of these advantages, the U.S. ion beam therapy community has expressed interests in helium ions as a potential candidate for ion beam therapy, especially pediatric cases. As such, characterizing the secondary nuclear fragment field created by primary helium ion interactions along the beam delivery devices and in human tissue is important for dose assessment and patient protection. Up to now the experimental data with respect to helium ions over the therapeutic energy range, 100 - 230 MeV/amu, is scarce compared to protons and carbon ions. Kurosawa et al. measured stopping target yields and angular spectra of neutrons, protons, deuterons and tritons produced by various target materials bombarded by 100- and 180- MeV/amu helium ions; Heilbronn et al. and Cecil et al. also measured the stopping target neutron yields by 155-, 160- and 177.5-MeV/amu helium ion bombardments. We have proposed to measure angular distributions of secondary neutrons and light charged ions produced by 100- and 230-MeV/amu helium ions bombarding stopping water and iron targets. The experiment was conducted at the Heavy Ion Medical Accelerator in Chiba (HIMAC) of the National Institute of Radiological Sciences (NIRS) in Japan this June. During the literature survey for experimental setup, we found that the ratio of the ion beam range (R) to the target depth (d) varies from 0.5 - 0.98 in the stopping target measurements either for helium ions incident on various targets or carbon ions bombarding targets as tissue surrogates. The difference in the values of ratio R/d makes comparison of experimental results complicated and require accurate corrections. Hence, how the R/d ratio and cross sectional area of the targets influence the angular distributions of secondary particles is investigated by using a Monte Carlo method in this study. The influence of the depth and the cross sectional area of stopping water and iron targets on the yield and the spectra of secondary particles induced by 100- and 230-MeV/amu He ions was studied by a Monte Carlo simulation code, PHITS. The secondary charged particles and secondary neutrons who come from breakup of projectiles are highly forward-focused, while the secondary particles produced by target breakup are nearly isotropic. As the energy of {sup 4}He ions increases from 100 MeV/amu to 230 MeV/amu, the normalized intensities of charged particles decrease more gently with increasing angles, whereas the neutron angular distribution falls quickly at angles smaller than 30 deg. and starts to exceed the normalized profile of 100 MeV/amu He from 60 deg. When the target depth increases, the impact on attenuation of secondary particles is more significant for lighter target mass and higher-energy projectiles at forward angles. Also, with deeper targets, more interactions occur between the secondary particles and the target elements, which results in more target-like fragments at large and backward angles. In respect of the cross sectional area of the stopping targets, the forward angular distributions are similar to the system with smaller cross sectional area of the targets; however, no general rule was found for how the large-angle distributions are affected by the target cross sectional area. (authors)

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2018

Synthesis of Post-fire Monitoring Activities in the Great Basin Desert, Mojave Desert, and Transition Zones

In the deserts of the American Southwest, fire return intervals of centuries to millennia are being replaced by fire return intervals of decades. This increased burn frequency has implications for post-closure management and long-term stewardship for Soils Corrective Action Units (CAUs) and Corrective Action Sites (CASs) on the Nevada National Security Site (NNSS), Tonopah Test Range, and Nevada Test and Training Range for which the U.S. Department of Energy (DOE), Environmental Management-Nevada (EM-NV) is responsible. For many CAUs and CASs, where closure-in-place alternatives were implemented or are being considered, there is a chance that these sites could burn over while they still pose a risk to the environment or human health given the long half-lives of some of the radionuclide contaminants of concern (COCs) (Shafer et al., 2007; Shafer and Gomes, 2009). Although it would have been ideal to conduct a fire-related study at a radionuclide contaminated site on the NNSS to determine how contaminated soils are transported post-fire, it was more practical to examine fires in environments analogous to where Soils Activity CAUs and CASs exist. Therefore, a series of studies were initiated at three radiologically uncontaminated analog sites to better understand the possible effects of wildfire on erosion and sediment transport by wind and water should vegetation at contaminated sites burn at the NNSS. The studies took place at the sites of the Gleason Fire, a prescribed burn that occurred near Ely, Nevada, which is in the Great Basin ecoregion; the White Rock Fire that occurred near Mesquite, Nevada, which is in the Mojave Desert ecoregion; and the Jacob Fire that occurred near Hiko, Nevada, in the transitional zone between the Great Basin Desert and the Mojave Desert. Each site was representative of one of the three ecoregions found on the NNSS. Erosion and vegetation characteristics were measured multiple times post-fire on both burned and unburned test plots at these study sites to compare and monitor the effects of fire over time. However, at the Mojave Desert site, there was an additional burn from nearly 25 years ago that was also compared with the more recent burned areas from 2013. Also, the time elapsed after the fire and the time when sampling began differed among the ecoregions. For example, at the Great Basin site, samples were collected prior to the fire and less than one month after the fire, whereas data collected at the Mojave Desert site did not occur until 22 months after the fire. The differences between the sample measurements and the time that elapsed after the fire may contribute to the variability in the data and the interpretations of the data. Runoff and water erosion were quantified through a series of rainfall and runoff simulation tests in which controlled amounts of water were delivered to the soil surface. Runoff data were collected from different microhabitats (e.g., undercanopies, interspace soils, ridges, and drainage areas). The data showed soil hydrophobicity (i.e., water repellency) on the Great Basin site for up to 12 months after the fire. The soil structure remained changed and weaker on the burned areas compared with the unburned areas for the three-year study period. Although runoff data at both the Great Basin site and transition zone site were highly variable, the post-fire runoff potential did not generally increase at either location after three years of monitoring. Mojave runoff did not differ much between fire ages or between burned and unburned areas, possibly because of the amount of vegetation growing on all three surfaces and because the fire intensity was likely lower relative to other ecoregions due to the amount of space between plants. Additionally, the measurements conducted on the Mojave fire occurred several years after the fire had burned and not within several months of the burn, which may also account for the lack of differences in runoff between burned and unburned locations. Wind erosion was assessed and quantified with a Portable In-Situ Wind ERosion Lab (PI-SWERL) on both the burned and unburned soils of different microhabitats (e.g., ridges, drainages, interspaces between plants, and plant undercanopies). Estimates of emissions (e.g., particulate matter with aerodynamic diameters less than or equal to 10 micrometers, or PM10) at different wind speeds were collected and filter samples were analyzed for chemical composition. The measurements among the fires were similar and the results of the wind erosion measurements indicate that there were seasonal influences on many parameters, but the potential for PM10 windblown dust emissions was higher on burned areas compared with unburned areas. Among the burned areas, drainages produced the most dust emissions, whereas burned ridges were the least emissive. Emissions at the Mojave site and transition zone site were similar between burned and unburned areas approximately three years after the respective fires. Emissions remained much greater on burned soils at the Great Basin site. However, site selection may have also contributed to the differences of emissions among the three study locations. Post-fire vegetation responses were documented for three years following each fire in different microhabitats (e.g., ridge, drainage, undercanopy, and interspace) at the Great Basin and transition zone sites. In 2013, at the Mojave fire site, random permanent plots were established in newly burned areas, areas that burned approximately 25 years ago, and an unburned control area. At each fire site, the regeneration of native plant species dominated the burned areas, but invasive annual grasses were present at each fire site. During the course of each three-year study, the invasive annual grasses increased in density or percentage at both the Great Basin and transition fire sites but not at the Mojave site, where annual invasive grasses remained high throughout the study period. However, the chronosequence data from the Mojave site indicate a transition to different invasive grass species with time. The post-burn vegetation at all three ecoregions is still in the early stages of succession, and shrub size should increase over time and shrub density should decrease over time. However, the recovery of the plant communities to pre-burn compositions may not occur for decades or centuries, or may not occur because of changes in climate and the presence of invasive annual grasses. Results from the three study locations suggested that contaminated soils on the NNSS that experienced wildfire had the potential for soil erosion and transport of contaminated soils. Both wind and soil runoff studies indicated that locations in the Great Basin and transition zone ecoregions were more susceptible to erosion than the Mojave Desert ecoregion, but the highest levels of erosion occurred during the early portions of the study (the first 24 months) and the Mojave Desert was not measured until 22 months after the burn. Additionally, data from the Great Basin indicated deeper soils may increase susceptibility to wind erosion. Historically, the Great Basin and transition zone ecoregions burned more frequently than the Mojave Desert because of fuel abundance and connectivity—and they continue to burn more frequently, particularly after the introduction of invasive grasses (Davies and Nafus, 2013). However, both ecoregions and the transition zone have burned with extensive, high-severity fires when certain weather and fuel conditions are met. For example, the high abundance and productivity of annual grasses and forbs—which are usually produced by above average winter precipitation—combined with early spring and summer warm, dry conditions. Future climate scenarios predict increased temperatures, variable to reduced precipitation, and larger, more extreme wildfires throughout western North America. These predictions suggest that future fires on the NNSS could increase in frequency, intensity, and severity similar to their analog ecosystems throughout the Great Basin and Mojave Desert (Dennison et al., 2014; Abatzoglou andWilliams, 2016; Westerling, 2016).

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Effect of intrafractional prostate motion on simultaneous boost intensity-modulated radiotherapy to the prostate: A simulation study based on intrafractional motion in the prone position

Although the prostate displacement of patients in the prone position is affected by respiration-induced motion, the effect of intrafractional prostate motion in the prone position during “simultaneous integrated boost intensity-modulated radiotherapy” (SIB-IMRT) is unclear. The purpose of this study was to evaluate the dosimetric effects of intrafractional motion on SIB-IMRT to a dominant intraprostatic lesion (IPL) using measured motion data of patients in a prone position, fixed with a thermoplastic shell. We obtained 2 orthogonal x-ray fluoroscopic images at the same moment every 0.2 seconds for 30 seconds before and after treatment, once weekly, from 7 patients with localized prostate cancer with detectable prostatic calcification. Prostate displacements in the left-right (LR), anteroposterior (AP), and superoinferior (SI) directions were calculated using the prostatic calcification as a fiducial marker. We defined the displacement between pretreatment and posttreatment as baseline drift (BD). An SIB-IMRT plan was generated in which each IPL + 3 mm received a dose of 94.5 Gy, whereas the remainder of the prostate + 7 mm received a dose of 75.6 Gy in 9 fields. A simulated plan of dose blurring was generated by the convolution of isocenter-shifted plans using measured motion data in 30 seconds and motion in 30 seconds + distance between pretreatment and posttreatment position (BD) for each of the 7 patients. The motion in 30 seconds mainly reflected respiration-induced motion. The mean displacements of BD were 1.4 mm (− 3.1 to 8.2 mm), − 2.2 mm (− 9.1 to 1.5 mm), and − 0.3 mm (− 5.0 to 1.8 mm) in the AP, SI, and LR directions, respectively. The differences in the target coverage with V{sub 90%} of the IPL and V{sub 100%} of the prostate between the simulated plan and original plan were − 3.9% to − 0.3% and − 0.6% to 1.1% for respiration-induced motion and 3.1% to − 67.8% and 3.6% to − 13.3% for BD with respiration-induced motion, respectively. The large motion of BD resulted in an inadequate coverage by the prescribed dose of the SIB-IMRT to the IPL. A 7-mm margin is recommended when real-time tracking techniques are not applied. The effect of respiration-induced motion was small, so long as a 3-mm margin was added.

61 RADIATION PROTECTION AND DOSIMETRY↗
DOE OSTI2013

Self-Management of Patient Body Position, Pose, and Motion Using Wide-Field, Real-Time Optical Measurement Feedback: Results of a Volunteer Study

Purpose: We present the results of a clinical feasibility study, performed in 10 healthy volunteers undergoing a simulated treatment over 3 sessions, to investigate the use of a wide-field visual feedback technique intended to help patients control their pose while reducing motion during radiation therapy treatment. Methods and Materials: An optical surface sensor is used to capture wide-area measurements of a subject's body surface with visualizations of these data displayed back to them in real time. In this study we hypothesize that this active feedback mechanism will enable patients to control their motion and help them maintain their setup pose and position. A capability hierarchy of 3 different level-of-detail abstractions of the measured surface data is systematically compared. Results: Use of the device enabled volunteers to increase their conformance to a reference surface, as measured by decreased variability across their body surfaces. The use of visual feedback also enabled volunteers to reduce their respiratory motion amplitude to 1.7 ± 0.6 mm compared with 2.7 ± 1.4 mm without visual feedback. Conclusions: The use of live feedback of their optically measured body surfaces enabled a set of volunteers to better manage their pose and motion when compared with free breathing. The method is suitable to be taken forward to patient studies.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

A quality assurance framework for the fully automated and objective evaluation of image quality in cone-beam computed tomography

Purpose: Thousands of cone-beam computed tomography (CBCT) scanners for vascular, maxillofacial, neurological, and body imaging are in clinical use today, but there is no consensus on uniform acceptance and constancy testing for image quality (IQ) and dose yet. The authors developed a quality assurance (QA) framework for fully automated and time-efficient performance evaluation of these systems. In addition, the dependence of objective Fourier-based IQ metrics on direction and position in 3D volumes was investigated for CBCT. Methods: The authors designed a dedicated QA phantom 10 cm in length consisting of five compartments, each with a diameter of 10 cm, and an optional extension ring 16 cm in diameter. A homogeneous section of water-equivalent material allows measuring CT value accuracy, image noise and uniformity, and multidimensional global and local noise power spectra (NPS). For the quantitative determination of 3D high-contrast spatial resolution, the modulation transfer function (MTF) of centrally and peripherally positioned aluminum spheres was computed from edge profiles. Additional in-plane and axial resolution patterns were used to assess resolution qualitatively. The characterization of low-contrast detectability as well as CT value linearity and artifact behavior was tested by utilizing sections with soft-tissue-equivalent and metallic inserts. For an automated QA procedure, a phantom detection algorithm was implemented. All tests used in the dedicated QA program were initially verified in simulation studies and experimentally confirmed on a clinical dental CBCT system. Results: The automated IQ evaluation of volume data sets of the dental CBCT system was achieved with the proposed phantom requiring only one scan for the determination of all desired parameters. Typically, less than 5 min were needed for phantom set-up, scanning, and data analysis. Quantitative evaluation of system performance over time by comparison to previous examinations was also verified. The maximum percentage interscan variation of repeated measurements was less than 4% and 1.7% on average for all investigated quality criteria. The NPS-based image noise differed by less than 5% from the conventional standard deviation approach and spatially selective 10% MTF values were well comparable to subjective results obtained with 3D resolution pattern. Determining only transverse spatial resolution and global noise behavior in the central field of measurement turned out to be insufficient. Conclusions: The proposed framework transfers QA routines employed in conventional CT in an advanced version to CBCT for fully automated and time-efficient evaluation of technical equipment. With the modular phantom design, a routine as well as an expert version for assessing IQ is provided. The QA program can be used for arbitrary CT units to evaluate 3D imaging characteristics automatically.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2012

A scaling transformation for classifier output based on likelihood ratio: Applications to a CAD workstation for diagnosis of breast cancer

Purpose: The authors developed scaling methods that monotonically transform the output of one classifier to the ''scale'' of another. Such transformations affect the distribution of classifier output while leaving the ROC curve unchanged. In particular, they investigated transformations between radiologists and computer classifiers, with the goal of addressing the problem of comparing and interpreting case-specific values of output from two classifiers. Methods: Using both simulated and radiologists' rating data of breast imaging cases, the authors investigated a likelihood-ratio-scaling transformation, based on ''matching'' classifier likelihood ratios. For comparison, three other scaling transformations were investigated that were based on matching classifier true positive fraction, false positive fraction, or cumulative distribution function, respectively. The authors explored modifying the computer output to reflect the scale of the radiologist, as well as modifying the radiologist's ratings to reflect the scale of the computer. They also evaluated how dataset size affects the transformations. Results: When ROC curves of two classifiers differed substantially, the four transformations were found to be quite different. The likelihood-ratio scaling transformation was found to vary widely from radiologist to radiologist. Similar results were found for the other transformations. Our simulations explored the effect of database sizes on the accuracy of the estimation of our scaling transformations. Conclusions: The likelihood-ratio-scaling transformation that the authors have developed and evaluated was shown to be capable of transforming computer and radiologist outputs to a common scale reliably, thereby allowing the comparison of the computer and radiologist outputs on the basis of a clinically relevant statistic.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Computational Modeling of Micrometastatic Breast Cancer Radiation Dose Response

Purpose: Prophylactic cranial irradiation (PCI) involves giving radiation to the entire brain with the goals of reducing the incidence of brain metastasis and improving overall survival. Experimentally, we have demonstrated that PCI prevents brain metastases in a breast cancer mouse model. We developed a computational model to expand on and aid in the interpretation of our experimental results. Methods and Materials: MATLAB was used to develop a computational model of brain metastasis and PCI in mice. Model input parameters were optimized such that the model output would match the experimental number of metastases per mouse from the unirradiated group. An independent in vivo–limiting dilution experiment was performed to validate the model. The effect of whole brain irradiation at different measurement points after tumor cells were injected was evaluated in terms of the incidence, number of metastases, and tumor burden and was then compared with the corresponding experimental data. Results: In the optimized model, the correlation between the number of metastases per mouse and the experimental fits was >95. Our attempt to validate the model with a limiting dilution assay produced 99.9% correlation with respect to the incidence of metastases. The model accurately predicted the effect of whole-brain irradiation given 3 weeks after cell injection but substantially underestimated its effect when delivered 5 days after cell injection. The model further demonstrated that delaying whole-brain irradiation until the development of gross disease introduces a dose threshold that must be reached before a reduction in incidence can be realized. Conclusions: Our computational model of mouse brain metastasis and PCI correlated strongly with our experiments with unirradiated mice. The results further suggest that early treatment of subclinical disease is more effective than irradiating established disease.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2017

{sup 18}F-Fluorodeoxyglucose/Positron Emission Tomography Predicts Patterns of Failure After Definitive Chemoradiation Therapy for Locally Advanced Non-Small Cell Lung Cancer

Background: We previously reported that pretreatment positron emission tomography (PET) identifies lesions at high risk for progression after concurrent chemoradiation therapy (CRT) for locally advanced non-small cell lung cancer (NSCLC). Here we validate those findings and generate tumor control probability (TCP) models. Methods: We identified patients treated with definitive, concurrent CRT for locally advanced NSCLC who underwent staging {sup 18}F-fluorodeoxyglucose/PET/computed tomography. Visible hypermetabolic lesions (primary tumors and lymph nodes) were delineated on each patient's pretreatment PET scan. Posttreatment imaging was reviewed to identify locations of disease progression. Competing risks analyses were performed to examine metabolic tumor volume (MTV) and radiation therapy dose as predictors of local disease progression. TCP modeling was performed to describe the likelihood of local disease control as a function of lesion size. Results: Eighty-nine patients with 259 hypermetabolic lesions (83 primary tumors and 176 regional lymph nodes) met the inclusion criteria. Twenty-eight patients were included in our previous report, and the remaining 61 constituted our validation cohort. The median follow-up time was 22.7 months for living patients. In 20 patients, the first site of progression was a primary tumor or lymph node treated with radiation therapy. The median time to progression for those patients was 11.5 months. Data from our validation cohort confirmed that lesion MTV predicts local progression, with a 30-month cumulative incidence rate of 23% for lesions above 25 cc compared with 4% for lesions below 25 cc (P=.008). We found no evidence that radiation therapy dose was associated with local progression risk. TCP modeling yielded predicted 30-month local control rates of 98% for a 1-cc lesion, 94% for a 10-cc lesion, and 74% for a 50-cc lesion. Conclusion: Pretreatment FDG-PET identifies lesions at risk for progression after CRT for locally advanced NSCLC. Strategies to improve local control should be tested on high-risk lesions, and treatment deintensification for low-risk lesions should be explored.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2018

Investigation of dose reduction in cardiac perfusion SPECT via optimization and choice of the image reconstruction strategy

Background: We investigated the extent to which the administered dose (activity) level can be reduced without sacrificing diagnostic accuracy for three reconstruction strategies for SPECT-myocardial perfusion imaging (MPI). Methods: We optimized the parameters of the three reconstruction strategies for perfusion-defect detection over a range of simulated administered dose levels using a set of hybrid studies (derived from 190 subjects) consisting of clinical SPECT-MPI data modified to contain realistic simulated lesions. The optimized strategies we considered are filtered backprojection (FBP) with no correction for degradations, ordered-subsets expectation-maximization (OS-EM) with attenuation correction (AC), scatter correction (SC), and resolution correction (RC), and OS-EM with scatter and resolution correction only. Each study was evaluated using a total perfusion deficit (TPD) score computed by the Quantitative Perfusion SPECT (QPS) software package. We conducted a receiver operating characteristics (ROC) study based on the TPD scores for each dose level and reconstruction strategy. Results: For FBP, the achieved optimum values of the area under the ROC curve (AUC) at 100%, 50%, 25%, and 12.5% of standard dose were 0.75, 0.74, 0.72, and 0.70, respectively, compared to 0.81, 0.79, 0.76, and 0.74 for OS-EM with AC–SC–RC and 0.78, 0.77, 0.74, 0.72 for OS-EM with SC–RC. Conclusions: Our results suggest that studies reconstructed by OS-EM with AC–SC–RC could possibly be reduced, on average, to 25% of the originally administered dose without causing diagnostic accuracy (AUC) to decrease below that of FBP.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

SU-E-T-630: Predictive Modeling of Mortality, Tumor Control, and Normal Tissue Complications After Stereotactic Body Radiotherapy for Stage I Non-Small Cell Lung Cancer

Purpose: While rates of local control have been well characterized after stereotactic body radiotherapy (SBRT) for stage I non-small cell lung cancer (NSCLC), less data are available characterizing survival and normal tissue toxicities, and no validated models exist assessing these parameters after SBRT. We evaluate the reliability of various machine learning techniques when applied to radiation oncology datasets to create predictive models of mortality, tumor control, and normal tissue complications. Methods: A dataset of 204 consecutive patients with stage I non-small cell lung cancer (NSCLC) treated with stereotactic body radiotherapy (SBRT) at the University of Pennsylvania between 2009 and 2013 was used to create predictive models of tumor control, normal tissue complications, and mortality in this IRB-approved study. Nearly 200 data fields of detailed patient- and tumor-specific information, radiotherapy dosimetric measurements, and clinical outcomes data were collected. Predictive models were created for local tumor control, 1- and 3-year overall survival, and nodal failure using 60% of the data (leaving the remainder as a test set). After applying feature selection and dimensionality reduction, nonlinear support vector classification was applied to the resulting features. Models were evaluated for accuracy and area under ROC curve on the 81-patient test set. Results: Models for common events in the dataset (such as mortality at one year) had the highest predictive power (AUC = .67, p < 0.05). For rare occurrences such as radiation pneumonitis and local failure (each occurring in less than 10% of patients), too few events were present to create reliable models. Conclusion: Although this study demonstrates the validity of predictive analytics using information extracted from patient medical records and can most reliably predict for survival after SBRT, larger sample sizes are needed to develop predictive models for normal tissue toxicities and more advanced machine learning methodologies need be consider in the future.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2020

The Influence of Aqueous Dispersivity on Transport of Radiological Material at LANL MDA G - 20450

Aqueous dispersivity is a phenomenon by which a solute moving in groundwater mixes with water that does not contain the solute and becomes diluted. Solutes take paths of varying lengths through pore networks or experience slower velocities due to interactions with pore walls. Aqueous dispersivity leads to breakthrough curves with earlier arrival than expected in purely advective systems and persistent 'tails,' or late-arriving, dilute concentrations of the solute. Dispersivity can be longitudinal (in the direction of flow) or transverse (orthogonal to flow). LANL has disposed of radioactive material at Material Disposal Area (MDA) G since the late 1950's. Most of the disposed materials at MDA G are low-level waste (LLW), but other types of radioactive wastes are disposed or stored at the site. For example, there is a collection of remote-handled transuranic waste (RH-TRU) waste in 33 shafts, which were intended to be stored retrievably. Aqueous-phase radionuclides included in models of contaminant transport at MDA G are subject to dispersive processes in porous media of the vadose zone and saturated zone. To model dispersivity at MDA G probabilistically, we created site-specific distributions of aqueous dispersivity. First, we performed a comprehensive review of peer-reviewed publications, reports from other performance assessments of MDA G, and documentation from sites that were considered similar based on expert opinion, such as Yucca Mountain. Data were included from a wide range of sources, so that distributions developed based on the data reflect the current state of knowledge in properties of the subsurface environment. Data were grouped based on value type (e.g., determined via experiment or used in a different model), rock type, zone type (saturated or unsaturated), and site, and were weighted in the distributions according to their relevance to the site and zone type. We combined Monte Carlo simulation and bootstrapping techniques to produce approximate distributions of mean aqueous dispersivity. Distributions of dispersivity for saturated and unsaturated zone transport are differentiated by data weight and the length scales over which transport occurs. We find that underestimating or disregarding transverse dispersivity may lead to overstating simulated well capture in the saturated zone at MDA G. Neglecting transverse dispersivity is a common assumption due in part to use of one-dimensional transport models that do not consider solute spreading orthogonal to flow. Also, we find that variability in longitudinal dispersivity is associated with substantial travel time alterations in the MDA G unsaturated zone and in simulated contaminant breakthrough times at a downstream observation plane in the MDA G saturated zone. Finally, at large scales (>1000 m), a linear trend between the dispersivity coefficient and length over which transport occurs may overestimate the dispersivity coefficient. Future modeling work with application to solute spreading could include interacting advective and diffusive zones in the highly fractured basalt below MDA G. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2018

When and how to treat an IMRT patient on a second accelerator without replanning?

When a linear accelerator is unavailable for treatment, a clinical decision is imminent regarding whether a patient should be treated on a linear accelerator other than the machine the patient was scheduled on, or whether treatment should be postponed until the original Linac becomes available. This work investigates the feasibility of switching patients to different accelerators for intensity-modulated radiation therapy (IMRT). We have performed Monte Carlo simulations of photon beams from different Linac models and vendors. Prostate and head and neck (H&N) treatment plans for Siemens Primus, Primart, and Varian 21EX accelerators are studied in this work. Dose distributions for given plans are recalculated using different beam data with the same nominal energy from different Linacs. We have compared dose-volume histograms (DVHs) and the maximum, the minimum, and the mean doses to the target and critical structures because of switching accelerators. In the process of switching a treatment plan to a different accelerator, issues exist, including optimum penumbra compensation, dose distribution at the boundary of target and critical structures, and multileaf collimator (MLC) leaf-width effects, which need to be considered and verified with measurements. Our Monte Carlo simulation results confirm that, for the cases we tested, the dose received by 95% of the planning target volume differs by 0.2% to 1.5% between Siemens Primus and Varian 21EX Linacs. The discrepancy is within our clinical acceptance criteria of 3% for IMRT treatments. In making the final decision on whether to switch machines or not, the tumor control probabilities (TCPs) based on a linear-quadratic model are compared. Based on the analyses performed in this work, it is therapeutically more beneficial to switch a patient to a different machine than to postpone a treatment until the original machine is available, especially for fast-growing tumors such as H&N cancers.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

An Image-Guided Study of Setup Reproducibility of Postmastectomy Breast Cancer Patients Treated With Inverse-Planned Intensity Modulated Radiation Therapy

Purpose: To calculate planning target volume (PTV) margins for chest wall and regional nodal targets using daily orthogonal kilovolt (kV) imaging and to study residual setup error after kV alignment using volumetric cone-beam computed tomography (CBCT). Methods and Materials: Twenty-one postmastectomy patients were treated with intensity modulated radiation therapy with 7-mm PTV margins. Population-based PTV margins were calculated from translational shifts after daily kV positioning and/or weekly CBCT data for each of 8 patients, whose surgical clips were used as surrogates for target volumes. Errors from kV and CBCT data were mathematically combined to generate PTV margins for 3 simulated alignment workflows: (1) skin marks alone; (2) weekly kV imaging; and (3) daily kV imaging. Results: The kV data from 613 treatment fractions indicated that a 7-mm uniform margin would account for 95% of daily shifts if patients were positioned using only skin marks. Total setup errors incorporating both kV and CBCT data were larger than those from kV alone, yielding PTV expansions of 7 mm anterior–posterior, 9 mm left–right, and 9 mm superior–inferior. Required PTV margins after weekly kV imaging were similar in magnitude as alignment to skin marks, but rotational adjustments of patients were required in 32% ± 17% of treatments. These rotations would have remained uncorrected without the use of daily kV imaging. Despite the use of daily kV imaging, CBCT data taken at the treatment position indicate that an anisotropic PTV margin of 6 mm anterior–posterior, 4 mm left–right, and 8 mm superior–inferior must be retained to account for residual errors. Conclusions: Cone-beam CT provides additional information on 3-dimensional reproducibility of treatment setup for chest wall targets. Three-dimensional data indicate that a uniform 7-mm PTV margin is insufficient in the absence of daily IGRT. Interfraction movement is greater than suggested by 2-dimensional imaging, thus a margin of at least 4 to 8 mm must be retained despite the use of daily IGRT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗