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At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

On Gibbs Equilibrium and Hillert Nonequilibrium Thermodynamics

During his time at Royal Institute of Technology (Kungliga Tekniska högskolan) in Sweden, the present author learned nonequilibrium thermodynamics from Mats Hillert. The key concepts are the separation of internal and external variables of a system and the definitions of potentials and molar quantities. In equilibrium thermodynamics derived by Gibbs, the internal variables are not independent and can be fully evaluated from given external variables. While irreversible thermodynamics led by Onsager focuses on internal variables though often mixed with external variables. Hillert integrated them together by first emphasizing their differences and then examining their connections. His philosophy was reflected by the title of his book “Phase Equilibria, Phase Diagrams and Phase Transformations” that puts equilibrium, nonequilibrium, and internal processes on equal footing. Here, in the present paper honoring Hillert, the present author reflects his experiences with Hillert and his work in last 40 years and expresses his gratitude for all the wisdom and support from him in terms of “Hillert nonequilibrium thermodynamics” and discusses some recent topics that the present author has been working on.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Implementation of the direct S ( α , β ) method in the KENO Monte Carlo code

The Monte Carlo code KENO contains thermal scattering data for a wide variety of thermal moderators. These data are processed from Evaluated Nuclear Data Files (ENDF) by AMPX and stored as double differential probability distribution functions. The method examined in this study uses S(α,β) probability distribution functions derived from the ENDF data files directly instead of being converted to double differential cross sections. This allows the size of the cross section data on the disk to be reduced substantially amount. KENO has also been updated to allow interpolation in temperature on these data so that problems can be run at any temperature. Results are shown for several simplified problems for a variety of moderators. In addition, benchmark models based on the KRITZ reactor in Sweden were run, and the results are compared with the previous versions of KENO without the direct S(α,β) method. Results from the direct S(α,β) method compare favorably with the original results obtained using the double differential cross sections. Finally, sampling the data increases the run-time of the Monte Carlo calculation, but memory usage is decreased substantially.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Analysis of new measurements of Calvert Cliffs spent fuel samples using SCALE 6.2

High quality experimental data for isotopic compositions in irradiated fuel are important to spent fuel applications, including nuclear safeguards, spent fuel storage, transportation, and final disposal. The importance of these data has been increasingly recognized in recent years, particularly as countries like Finland and Sweden plan to open the world’s first two spent fuel geological repositories in 2020s, while other countries, including the United States, are considering extended dry fuel storage options. Destructive and nondestructive measurements of a spent fuel rod segment from a Combustion Engineering 14 × 14 fuel assembly of the Calvert Cliffs Unit 1 nuclear reactor have been recently performed at Oak Ridge National Laboratory (ORNL). These ORNL measurements included two samples selected from adjacent axial locations of a fuel rod with initial enrichment of 3.038 wt% 235 U, which achieved burnups close to 43.5 GWd/MTU. More than 50 different isotopes of 16 elements were measured using high precision measurement methods. Various investigations have assessed the quality of the new ORNL measurement data, including comparison to previous measurements and to calculation results. Previous measurement data for samples from the same fuel rod measured at ORNL are available from experiments performed at Pacific Northwest National Laboratory in the United States and the Khoplin Radium Institute in Russia. Detailed assembly models were developed using the newly released SCALE 6.2 code package to simulate depletion and decay of the measured fuel samples. Furthermore, results from this work show that the new ORNL measurements provide a good quality radiochemical assay data set for spent fuel with relatively high burnup and long cooling time, and they can serve as good benchmark data for nuclear burnup code validation and spent fuel studies.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Using E-PRTR data on point source emissions to air and water—First steps towards a national chemical footprint

There is a great need for indicators to monitor the use and potential impacts of hazardous chemicals. Today there is a huge lack of data, methods and results and method development and studies should be given urgent priority. The aim of this paper was to develop and test an approach to calculate the potential environmental impacts of chemicals for a whole country using the E-PRTR (European Pollutant Release and Transfer Register) as a database and Sweden as an example. Swedish data from 2008 on emissions to air and water for 54 substances from point sources were retrieved from an open database. The data were transformed and aggregated using USEtox, a life-cycle impact assessment (LCIA) method for calculating potential human toxicity and ecotoxicity, both from industrial emissions directly and after input–output analysis (IO analysis) to reallocate emissions to product categories. Zinc to air and water contributed most to human toxicity followed by mercury to air. The largest contribution by industry to potential human toxicity came from the metal industry, followed by the paper and paper product industry. For potential ecotoxicity, zinc, fluoranthene and copper contributed the most. The largest contributions by industry came from the paper and paper products manufacturing sector, followed by the basic metals manufacturing sector. The approach used here can be seen as the first step towards a chemical footprint for nations. By adding data from other countries and other sources, a more complete picture can be gained in line with other footprint calculations. Furthermore, diffuse emissions from, for example, transport or emissions of pesticides could also be added for a more holistic assessment. Since the area of chemicals is complicated, it is probably necessary to develop and use several indicators that complement each other. It is suggested that the approach outlined here could be useful in developing a method for establishing a national chemical footprint. - Highlights: • European Pollutant and Transfer Register (E-PRTR) used to develop indicators • Study combined emissions to air and water from E-PRTR with USEtox and IO analysis • Metals and especially zinc contributed most to potential human toxicity and ecotoxicity • Paper and metal industries contribute most to potential human toxicity and ecotoxicity • This new assessment could be used by many countries and can be developed further.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Updated indicators of Swedish national human toxicity and ecotoxicity footprints using USEtox 2.01

In a recent paper, Sörme et al. (Environ. Impact Assess. Rev., 56, 2016), took a first step towards an indicator of a national chemical footprint, and applied it to Sweden. Using USEtox 1.01, they calculated national impact potentials for human toxicity and ecotoxicity. The results showed that zinc dominated impacts, both for human toxicity and ecotoxicity. We calculated updated indicators of the Swedish national human toxicity and ecotoxicity footprint using USEtox 2.01. We also compared impact potentials based on USEtox with the mass of chemical emissions. The two model versions produced relatively consistent results. Zinc is still a major contributor to the human toxicity and ecotoxicity impact potentials when characterized with USEtox 2.01. The mass-based indicator pinpoints somewhat different substances than the impact-based indicators. - Highlights: • USEtox 1.01 and 2.01 are relatively consistent in identifying the substances with largest impact potentials. • Metals were identified as a priority group of substances for both human toxicity and ecotoxicity. • Zinc is a major contributor to the human toxicity impact potential, in both model versions. • Zinc’s dominance concerning human toxicity sharply contrasts results from other studies: this is somewhat of a paradox. • Using the mass of chemical emissions as a simplified indicator pinpoints somewhat different substances.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2014

Cadmium, type 2 diabetes, and kidney damage in a cohort of middle-aged women

Background: It has been proposed that diabetic patients are more sensitive to the nephrotoxicity of cadmium (Cd) compared to non-diabetics, but few studies have examined this in humans, and results are inconsistent. Aim: To test the hypothesis that women with type 2 diabetes mellitus (DM) or impaired glucose tolerance (IGT) have higher risk of kidney damage from cadmium compared to women with normal glucose tolerance (NGT). Methods: All 64-year-old women in Gothenburg, Sweden, were invited to a screening examination including repeated oral glucose tolerance tests. Random samples of women with DM, IGT, and NGT were recruited for further clinical examinations. Serum creatinine was measured and used to calculate estimated glomerular filtration rate (eGFR). Albumin (Alb) and retinol-binding protein (RBP) were analyzed in a 12 h urine sample. Cadmium in blood (B-Cd) and urine (U-Cd) was determined using inductively coupled plasma mass spectrometry. Associations between markers of kidney function (eGFR, Alb, and RBP) and quartiles of B-Cd and U-Cd were evaluated in models, including also blood pressure and smoking habits. Results: The mean B-Cd (n=590) was 0.53 µg/L (median 0.34 µg/L). In multivariable models, a significant interaction was seen between high B-Cd (upper quartile, >0.56 µg/L) and DM (point estimate +0.40 mg Alb/12 h, P=0.04). In stratified analyzes, the effect of high B-Cd on Alb excretion was significant in women with DM (53% higher Alb/12 h, P=0.03), but not in women with IGT or NGT. Models with urinary albumin adjusted for creatinine showed similar results. In women with DM, the multivariable odds ratio (OR) for microalbuminuria (>15 mg/12 h) was increased in the highest quartile of B-Cd vs. B-Cd quartiles 1–3 in women with DM (OR 4.2, 95% confidence interval 1.1–12). No such effect was found in women with IGT or NGT. There were no associations between B-Cd and eGFR or excretion of RBP, and no differences between women with DM, IGT, or NGT regarding effect of B-Cd on eGFR or RBP. Conclusion: The present study provides support for the hypothesis that women with DM have higher risk of renal glomerular damage from cadmium exposure compared to women without DM. - Highlights: • Cadmium in blood, kidney function, and glucose tolerance was examined in 590 women. • Blood cadmium was associated with albumin excretion in women with type 2 diabetes. • No such associations with cadmium were found in women without diabetes. • Women with type 2 diabetes have increased sensitivity to kidney damage from cadmium.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

Cadmium and mercury exposure over time in Swedish children

Purpose: Knowledge about changes in exposure to toxic metals over time remains very sparse, in particular for children, the most vulnerable group. Here, we assessed whether a reduction in environmental pollution with cadmium (Cd) and mercury (Hg) caused a change in exposure over time. In total, 1257 children (age 4–9) in two towns in Sweden were sampled once in 1986–2013. Blood concentrations of Cd (b-Cd; n=1120) and Hg (b-Hg; n=560) were determined. Results: The median b-Cd was 0.10 (geometric mean 0.10; range 0.010–0.61) μg/L and b-Hg was 0.91 (geometric mean 0.83; range 0.021–8.2) μg/L. Children living close to a smelter had higher b-Cd and b-Hg than those in urban and rural areas. There was no sex difference in b-Cd or b-Hg, and b-Cd and b-Hg showed no significant accumulation by age. b-Cd decreased only slightly (0.7% per year, p<0.001) over the study period. In contrast, b-Hg did show a clear decrease over the study period (3% per year, p<0.001). Conclusions: The exposure to Cd was very low but still might increase the risk of disease later in life. Moreover, b-Cd only showed a minor decrease, indicating that Cd pollution should be further restricted. b-Hg was relatively low and decreasing, probably because of reduced use of dental amalgam and lower Hg intake from fish. The b-Cd and b-Hg levels decreased much less than the levels of lead in the blood as previously found in the same children. - Highlights: • There are few studies of time trends for exposure to toxic metals, except for lead. • 1986–2013 we studied blood levels of cadmium and mercury in 1257 Swedish children. • The median blood concentration of cadmium was 0.10 μg/L, of mercury 0.83 μg/L. • Cadmium perhaps decreased by 0.7% per year, mercury by 3% per year. • Cadmium accumulation may result in toxic levels in elderly women.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2017

Stories about ourselves: How national narratives influence the diffusion of large-scale energy technologies

Examining past examples of rapid, transformational changes in energy technologies could help governments understand the factors associated with such transitions. We used an existing dataset to assess government strategies to connect new energy technologies with national narratives. Analyzing the diffusion stories told by experts, we demonstrate how governments connected the new technologies with their national narratives. The United States government supported the development of nuclear power after World War II with the national narrative that the United States was destined to improve creation, increasing the potential of raw materials exponentially for the nation’s good (“atoms for peace,” electricity “too cheap to meter”). In Brazil, the development of sugar cane ethanol was supported by the government’s invoking the national narrative of suffering leading to knowledge and redemption, coupled with the quest for improved societal well-being (technological development to produce ethanol and employment for farmers). In Sweden, biomass energy was tied to the national narrative of local control, as well as love of nature and tradition (the use of natural products). We found strong evidence that the pairing of technological transformations with national narratives facilitated the successful development and implementation of these major energy technologies in the three cases analyzed here.

99 GENERAL AND MISCELLANEOUS↗
DOE OSTI2016

Diverse origins of Arctic and Subarctic methane point source emissions identified with multiply-substituted isotopologues

Methane is a potent greenhouse gas, and there are concerns that its natural emissions from the Arctic could act as a substantial positive feedback to anthropogenic global warming. Determining the sources of methane emissions and the biogeochemical processes controlling them is important for understanding present and future Arctic contributions to atmospheric methane budgets. We apply measurements of multiply-substituted isotopologues, or clumped isotopes, of methane as a new tool to identify the origins of ebullitive fluxes in Alaska, Sweden and the Arctic Ocean. When methane forms in isotopic equilibrium, clumped isotope measurements indicate the formation temperature. In some microbial methane, however, non-equilibrium isotope effects, probably related to the kinetics of methanogenesis, lead to low clumped isotope values. We identify four categories of emissions in the studied samples: thermogenic methane, deep subsurface or marine microbial methane formed in isotopic equilibrium, freshwater microbial methane with non-equilibrium clumped isotope values, and mixtures of deep and shallow methane (i.e., combinations of the first three end members). Mixing between deep and shallow methane sources produces a non-linear variation in clumped isotope values with mixing proportion that provides new constraints for the formation environment of the mixing end-members. Analyses of microbial methane emitted from lakes, as well as a methanol-consuming methanogen pure culture, support the hypothesis that non-equilibrium clumped isotope values are controlled, in part, by kinetic isotope effects induced during enzymatic reactions involved in methanogenesis. Our results indicate that these kinetic isotope effects vary widely in microbial methane produced in Arctic lake sediments, with non-equilibrium Δ 18 values spanning a range of more than 5‰.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Modeling gas migration through clay-based buffer material using coupled multiphase fluid flow and geomechanics with stress-dependent gas permeability

A model for gas migration through clay-based buffer material is developed for modeling gas generation and migration associated with deep geologic nuclear waste disposal. The model is based on a multiphase fluid flow and geomechanics simulator that is adapted to consider enhanced gas flow when gas pressure is high enough to approach the confining stress magnitude. A key feature in the model is a direct coupling between gas permeability and stress, through a non-linear stress-dependent permeability function. The model was first tested and calibrated by modelling two different laboratory gas migration tests on Wyoming (MX-80) bentonite samples. The calibrated model was then applied to model gas migration through a bentonite buffer of a large-scale gas injection test (Lasgit) conducted at the Äspö Hard Rock Laboratory in Sweden. Observed preferential gas migration along interfaces (between compacted blocks and along the canister surface) required explicit representation of such interfaces in the model. The model with the stress-dependent gas permeability accurately captured observed experimental responses in terms of gas breakthrough time, peak gas pressure, and cumulative gas flow rates. The calibrated model was finally applied to simulate migration of hydrogen gas generated within a breached nuclear waste canister over 10,000 years, involving migration of much larger gas volumes. For the considered gas generation rate and host rock properties, the generated gas could migrate through the bentonite buffer and released into the surrounding host rock at a maximum gas pressure somewhat higher than the initial total stress, though a significant amount of hydrogen remained within the buffer. This modelling sets the stage for further detailed analysis of the impact of hydrogen gas generation on the long-term performance of nuclear waste repositories.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2025

A comparative analysis of numerical approaches for the description of gas flow in clay-based repository systems: From a laboratory to a large-scale gas injection test

There is nowadays a consensus among many countries that geological disposal is a favourable solution for the long-term management. Although different host formations and different barrier systems are under consideration around the world, clay-based materials form an important component for waste isolation in most national programmes. Hence, a good comprehension of the effect of gas flow on the hydro-mechanical behaviour of clay-based soils is essential, both at laboratory and field scale. Task B under the international cooperative project DECOVALEX-2023 has recently shown that, after some enhancement, models can be employed to reproduce laboratory scale tests, even with different sample geometries 37 . However, further work is required to understand whether they can be applied to simulate a large-scale experiment. Up-scaling of models for the advective transport of gas through clay-based low permeable material presents a number of problems related to the difficulty in obtaining consistent hydrogeological parameters and constitutive relationships at both laboratory and field scale. Based on a unique dataset from a large-scale gas injection test (Lasgit) performed at the Äspö Hard Rock Laboratory (Sweden), Task B within DECOVALEX-2023 has explored the refinement of these numerical strategies applied to the simulation of gas flow. Work performed within the task reveals that codes do not need to be substantially modified from the laboratory models to reproduce full-scale tests: indeed, model parameters calibrated and validated at laboratory scale have been applied to predict field scale gas flow at Lasgit, including peak gas pressure and injected cumulative gas volume. By means of (1) the introduction of interfaces between blocks to reflect the experimental configuration and the (2) adjustment of some parameters (e.g., higher permeability), the updated models are able to represent most of the key features observed in the experimental data, even at a large scale.

Tamayo-Mas, E↗
DOE OSTI2016

Acute Toxicity Grade 3 and 4 After Irradiation in Children and Adolescents: Results From the IPPARCA Collaboration

Purpose: In the context of oncologic therapy for children, radiation therapy is frequently indicated. This study identified the frequency of and reasons for the development of high-grade acute toxicity and possible sequelae. Materials and Methods: Irradiated children have been prospectively documented since 2001 in the Registry for the Evaluation of Side Effects After Radiation in Childhood and Adolescence (RiSK) database in Germany and since 2008 in the registry for radiation therapy toxicity (RADTOX) in Sweden. Data were collected using standardized, published forms. Toxicity classification was based on Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer criteria. Results: As of June 2013, 1500 children have been recruited into the RiSK database and 485 into the RADTOX registry leading to an analysis population of 1359 patients (age range 0-18). A total of 18.9% (n=257) of all investigated patients developed high-grade acute toxicity (grades 3/4). High-grade toxicity of the bone marrow was documented for 63.8% (n=201) of those patients, oral mucositis for 7.6% (n=24), and dermatitis for 7.6% (n=24). Patients with high-grade acute toxicity received concomitant chemotherapy more frequently (56%) than patients with no or lower acute toxicity (31.5%). In multivariate analyses, concomitant chemotherapy, diagnosis of Ewing sarcoma, and total radiation dose showed a statistically noticeable effect (P≤.05) on acute toxicity, whereas age, concomitant chemotherapy, Hodgkin lymphoma, Ewing sarcoma, total radiation dose, and acute toxicity influenced the time until maximal late toxicity. Conclusions: Generally, high-grade acute toxicity after irradiation in children and adolescence occurs in a moderate proportion of patients (18.9%). As anticipated, the probability of acute toxicity appeared to depend on the prescribed dose as well as concomitant chemotherapy. The occurrence of chronic toxicity correlates with the prior acute toxicity grade. Age seems to influence the time until maximal late toxicity but not the development of acute toxicity.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Multi-institutional Validation Study of Commercially Available Deformable Image Registration Software for Thoracic Images

Purpose: To assess the accuracy of the commercially available deformable image registration (DIR) software for thoracic images at multiple institutions. Methods and Materials: Thoracic 4-dimensional (4D) CT images of 10 patients with esophageal or lung cancer were used. Datasets for these patients were provided by DIR-lab ( (dir-lab.com)) and included a coordinate list of anatomic landmarks (300 bronchial bifurcations) that had been manually identified. Deformable image registration was performed between the peak-inhale and -exhale images. Deformable image registration error was determined by calculating the difference at each landmark point between the displacement calculated by DIR software and that calculated by the landmark. Results: Eleven institutions participated in this study: 4 used RayStation (RaySearch Laboratories, Stockholm, Sweden), 5 used MIM Software (Cleveland, OH), and 3 used Velocity (Varian Medical Systems, Palo Alto, CA). The ranges of the average absolute registration errors over all cases were as follows: 0.48 to 1.51 mm (right-left), 0.53 to 2.86 mm (anterior-posterior), 0.85 to 4.46 mm (superior-inferior), and 1.26 to 6.20 mm (3-dimensional). For each DIR software package, the average 3-dimensional registration error (range) was as follows: RayStation, 3.28 mm (1.26-3.91 mm); MIM Software, 3.29 mm (2.17-3.61 mm); and Velocity, 5.01 mm (4.02-6.20 mm). These results demonstrate that there was moderate variation among institutions, although the DIR software was the same. Conclusions: We evaluated the commercially available DIR software using thoracic 4D-CT images from multiple centers. Our results demonstrated that DIR accuracy differed among institutions because it was dependent on both the DIR software and procedure. Our results could be helpful for establishing prospective clinical trials and for the widespread use of DIR software. In addition, for clinical care, we should try to find the optimal DIR procedure using thoracic 4D-CT data.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2022

Using STAX data to predict IMS radioxenon concentrations

The noble gas collection and measurement stations in the International Monitoring System (IMS) are heavily influenced by releases from medical isotope production facilities. The ability to reliably model the movement of radioxenon from the points of release to these IMS samplers has improved enough that a routine aspect of the analysis of IMS radioxenon data should be the prediction of the effect of releases from civilian nuclear facilities on the sample concentrations. In this work, predicted concentrations at IMS noble gas systems in Germany and Sweden based on measured releases from Institute for Radioelements (IRE) in Belgium and atmospheric transport modeling for a four-month period are presented and discussed.

63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTAN↗
DOE OSTI2023

Experimental review of the performances of protective coatings for interconnects in solid oxide fuel cells

Ferritic stainless-steel interconnects are used in solid oxide fuel cells; however, coatings are required to improve their performance. Although several types of coatings have been proposed, they have been scarcely investigated under similar conditions. This study compares the characteristics of uncoated Crofer 22 APU and eight different coatings on Crofer 22 APU for up to 3,000 hours at 800°C. The coatings were deposited at various research laboratories around the world, and the experiments were performed at Chalmers University of Technology, Sweden. Cross-sections of the samples were analysed using scanning electron microscopy and energy-dispersive x-ray spectroscopy. The (Co,Mn)-based coated steels showed more than 50-fold lower chromium evaporation and at least 3 times thinner Cr 2 O 3 scale thickness compared to uncoated steel. The coated steel samples showed lower area-specific resistance (ASR) values than the uncoated steel after 3,000 hours of exposure, irrespective of the coating thickness, composition and deposition method.

25 ENERGY STORAGE↗
DOE OSTI2014

Multicriteria optimization informed VMAT planning

We developed a patient-specific volumetric-modulated arc therapy (VMAT) optimization procedure using dose-volume histogram (DVH) information from multicriteria optimization (MCO) of intensity-modulated radiotherapy (IMRT) plans. The study included 10 patients with prostate cancer undergoing standard fractionation treatment, 10 patients with prostate cancer undergoing hypofractionation treatment, and 5 patients with head/neck cancer. MCO-IMRT plans using 20 and 7 treatment fields were generated for each patient on the RayStation treatment planning system (clinical version 2.5, RaySearch Laboratories, Stockholm, Sweden). The resulting DVH of the 20-field MCO-IMRT plan for each patient was used as the reference DVH, and the extracted point values of the resulting DVH of the MCO-IMRT plan were used as objectives and constraints for VMAT optimization. Weights of objectives or constraints of VMAT optimization or both were further tuned to generate the best match with the reference DVH of the MCO-IMRT plan. The final optimal VMAT plan quality was evaluated by comparison with MCO-IMRT plans based on homogeneity index, conformity number of planning target volume, and organ at risk sparing. The influence of gantry spacing, arc number, and delivery time on VMAT plan quality for different tumor sites was also evaluated. The resulting VMAT plan quality essentially matched the 20-field MCO-IMRT plan but with a shorter delivery time and less monitor units. VMAT plan quality of head/neck cancer cases improved using dual arcs whereas prostate cases did not. VMAT plan quality was improved by fine gantry spacing of 2 for the head/neck cancer cases and the hypofractionation-treated prostate cancer cases but not for the standard fractionation–treated prostate cancer cases. MCO-informed VMAT optimization is a useful and valuable way to generate patient-specific optimal VMAT plans, though modification of the weights of objectives or constraints extracted from resulting DVH of MCO-IMRT or both is necessary.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Advantages and limitations of navigation-based multicriteria optimization (MCO) for localized prostate cancer IMRT planning

Efficacy of inverse planning is becoming increasingly important for advanced radiotherapy techniques. This study’s aims were to validate multicriteria optimization (MCO) in RayStation (v2.4, RaySearch Laboratories, Sweden) against standard intensity-modulated radiation therapy (IMRT) optimization in Oncentra (v4.1, Nucletron BV, the Netherlands) and characterize dose differences due to conversion of navigated MCO plans into deliverable multileaf collimator apertures. Step-and-shoot IMRT plans were created for 10 patients with localized prostate cancer using both standard optimization and MCO. Acceptable standard IMRT plans with minimal average rectal dose were chosen for comparison with deliverable MCO plans. The trade-off was, for the MCO plans, managed through a user interface that permits continuous navigation between fluence-based plans. Navigated MCO plans were made deliverable at incremental steps along a trajectory between maximal target homogeneity and maximal rectal sparing. Dosimetric differences between navigated and deliverable MCO plans were also quantified. MCO plans, chosen as acceptable under navigated and deliverable conditions resulted in similar rectal sparing compared with standard optimization (33.7 ± 1.8 Gy vs 35.5 ± 4.2 Gy, p = 0.117). The dose differences between navigated and deliverable MCO plans increased as higher priority was placed on rectal avoidance. If the best possible deliverable MCO was chosen, a significant reduction in rectal dose was observed in comparison with standard optimization (30.6 ± 1.4 Gy vs 35.5 ± 4.2 Gy, p = 0.047). Improvements were, however, to some extent, at the expense of less conformal dose distributions, which resulted in significantly higher doses to the bladder for 2 of the 3 tolerance levels. In conclusion, similar IMRT plans can be created for patients with prostate cancer using MCO compared with standard optimization. Limitations exist within MCO regarding conversion of navigated plans to deliverable apertures, particularly for plans that emphasize avoidance of critical structures. Minimizing these differences would result in better quality treatments for patients with prostate cancer who were treated with radiotherapy using MCO plans.

61 RADIATION PROTECTION AND DOSIMETRY↗