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At least 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Mechanical properties, failure mechanisms, and scaling laws of bicontinuous nanoporous metallic glasses

Molecular dynamics simulations are employed to study the mechanical properties of nanoporous Cu x Zr 1-x metallic glasses (MGs) with five different compositions, x = 0.28, 0.36, 0.50, 0.64, and 0.72, and porosity in the range 0.1 < Φ < 0.7. Results from tensile loading simulations indicate a strong dependence of Young's modulus, E, and Ultimate Tensile Strength (UTS) on porosity and composition. By increasing the porosity from Φ = 0.1 to Φ = 0.7, the topology of the nanoporous MG shifts from closed cell to open-cell bicontinuous. The change in nanoporous topology enables a brittle-to-ductile transition in deformation and failure mechanisms from a single critical shear band to necking and rupture of ligaments. Genetic Programming (GP) is employed to find scaling laws for E and UTS as a function of porosity and composition. Here, a comparison of the GP-derived scaling laws against existing relationships shows that the GP method is able to uncover expressions that can predict accurately both the values of E and UTS in the whole range of porosity and compositions considered.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Unraveling kinking: A plasticity enhancing failure mode in high strength nano metallic laminates

Kinking is an important and plasticity-enhancing deformation/failure mode in numerous mechanically anisotropic materials including high-strength nano metallic laminates (NMLs). However, our current limited understanding of the mechanics of kinking and its dependence on microstructural attributes is insufficient for thoroughly comprehending and eventually being able to control failure behaviors of materials. In this study, we investigate kinking dependencies on microstructural attributes in NMLs via in situ micropillar compression, multiscale microstructure characterization, dislocation dynamic simulations, and crystal plasticity modeling. Additionally, by examining several NML systems (Cu/Fe, Ag/Fe, Al-4Mg/Fe), we demonstrate that the development of internal stresses during loading activates local layer-parallel glide triggering kinking in NMLs. Furthermore, this work reveals the effect of key microstructural features including layer thickness, layer waviness, interface barrier strength, and work hardening capacity on kink band formation in NMLs. More broadly, our efforts represent a generically applicable approach for probing large-strain deformation behavior of complex materials via synergetic modeling and experimental efforts.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Integrated Transcriptomic and Proteomic Analysis Identifies Plasma Biomarkers of Hepatocellular Failure in Alcohol-Associated Hepatitis

Alcohol-associated hepatitis (AH) is a form of liver failure with high short-term mortality. Recent results have shown that HNF4a defective function and systemic inflammation are major disease drivers of AH. Plasma biomarkers of hepatocyte function could be useful for diagnostic and prognostic purposes. Herein an integrative analysis of hepatic RNAseq and liquid chromatography-tandem mass spectrometry (LC-MS/MS) was performed to identify plasma protein signatures for mild and severe AH patients. Alcohol-related liver disease cirrhosis (ALD)(AC), non-alcoholic fatty liver disease (NALFD), and healthy subjects (HC) were used as comparator groups. Identified proteins primarily involved in hepatocellular function were decreased in AH patients which included hepatokines, clotting factors, complement cascade components, and hepatocyte growth activators. A protein signature of AH disease severity was identified including thrombin (THRB), hepatocyte growth factor alpha (HGFA), clusterin (CLUS), human serum factor H-related protein (FHR1) and kallistatin (KAIN), which exhibited large abundance shifts between severe and non-severe AH. The combination of THRB and HGFA discriminated between severe and non-severe AH with high sensitivity and specificity. These findings were correlated with the liver expression of genes encoding secreted proteins in a similar cohort, finding a highly consistent plasma protein signature reflecting HNF4A and HNF1A functions. This unbiased proteomic-transcriptome analysis identified plasma protein signatures and pathways associated with disease severity, reflecting HNF4A/1A activity useful for diagnostic assessment in AH.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Prevalence of NS5A resistance associated variants in NS5A inhibitor treatment failures and an effective treatment for NS5A-P32 deleted hepatitis C virus in humanized mice

Highlights: • NS5A-P32 deletions were detected in 4.3% of genotype 1 HCV-infected patients with prior NS5A inhibitors treatment failure. • Efficacy of glecaprevir and pibrentasvir treatment for NS5A-P32 deleted HCV is lower compared to the wild-type strain. • Sofosbuvir plus glecaprevir and pibrentasvir combination treatment was effective for NS5A-P32del in humanized mice. Patients with chronic hepatitis C virus (HCV) infection who have failed to respond to direct-acting antiviral (DAA) treatment often acquire drug resistance-associated variants (RAVs). The NS5A-P32 deletion (P32del) RAV confers potent resistance to NS5A inhibitors; therefore, patients who acquire this deletion are likely to fail to respond to DAA re-treatment. We investigated the prevalence of N55A-P32del in patients who failed to respond to prior NS5A inhibitor treatment using direct sequencing and analyzed the efficacy of DAA combination treatment in the presence of NS5A-P32del RAVs using human hepatocyte transplanted mice. NS5A-P32del was detected in one of 23 (4.3%) patients who had failed to respond to prior NS5A inhibitor treatment. Although four weeks of NS3/4A protease inhibitor glecaprevir plus NS5A inhibitor pibrentasvir treatment effectively suppressed HCV replication in wild-type HCV-infected mice, serum HCV RNA never became negative in P32del HCV-infected mice. When P32del HCV-infected mice were treated with four weeks of glecaprevir plus pibrentasvir combined with the NS5B polymerase inhibitor sofosbuvir, serum HCV RNA became negative, and the virus was eliminated from the liver in three out of four mice. We conclude that the combination of sofosbuvir and glecaprevir plus pibrentasvir may be an effective new treatment option for patients with NS5A-P32del.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2021

Piezoelectric response and failure behavior of cement paste under external loading

We study the elastic behavior and rupture mechanism of Calcium Silicate Hydrates (C-S-H) in response to tensile loading. For the three tensile axes, initial defects are spotted in the interlayer regions. However, the crack propagation is rather different depending on the axis of tensile. The cup-and-cone failure surface shows the ductile feature of C-S-H in the x and y directions; while the devastating rupture mode confirms the brittle feature of C-S-H in the z direction. Piezoelectricity was investigated using the charge fluctuation method. The polarization variation in response to small strain was also investigated and piezoelectric coefficients were derived. Furthermore, dependence of elastic and piezoelectric properties over external pressure was analyzed. Results reveal an improvement of the mechanical properties and the ultimate strength especially in the z direction; whereas the non-piezoelectricity remains unchanged despite the rearrangement of atoms induced by the external applied pressure.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Understanding the plasticity contributions during laser-shock loading and spall failure of Cu microstructures at the atomic scales

A hybrid atomic-scale and continuum modeling framework is used to study the microstructural evolution during the laser-induced shock deformation and failure (spallation) of copper microstructures. A continuum two-temperature model (TTM) is used to account for the interaction of Cu atoms with a laser in molecular dynamics (MD) simulations. The MD-TTM simulations study the effect of laser loading conditions (laser fluence) on the microstructure (defects) evolution during various stages of shock wave propagation, reflection, and interaction in single-crystal (sc) Cu systems. In addition, the role of the microstructure is investigated by comparing the defect evolution and spall response of sc-Cu and nanocrystalline (nc) Cu systems. The defect (stacking faults and twin faults) evolution behavior in the metal at various times is further characterized using virtual in situ selected area electron diffraction and x-ray diffraction during various stages of evolution of microstructure. Here, the simulations elucidate the uncertain relation between spall strength and strain-rate and the much stronger relation between the spall strength and the temperatures generated due to laser shock loading for the small Cu sample dimensions considered here.

36 MATERIALS SCIENCE↗
DOE OSTI2020

A scale-invariant bonded particle model for simulating large deformation and failure of continua

In this paper, a scale-invariant bond model for simulating two-dimensional large deformation of continua is presented. An accurate torque form caused by relative rotation between bonded particles is derived based on beam theory. Validations of the proposed bond model are carried out by large deformation simulations of a simply supported beam subjected to central loading and a cantilever beam with end loading. Comparison of simulations with analytical solutions show a very good agreement. Later, Brazilian tests are simulated to demonstrate the ability of the framework to model failure and fracture process of rock.

58 GEOSCIENCES↗
DOE OSTI2025

Damage progression and failure of SiC/SiC composite tubes under hard-contact radial expansion

The response of silicon carbide (SiC) fiber-reinforced SiC matrix (SiC/SiC) composite cladding to mechanical interaction with fissile fuel is a knowledge gap that must be overcome to design and assess SiC-based cladding systems for advanced nuclear applications. This study developed the relevant mechanical testing capability and identified the failure behavior and the critical microstructural features and processing defects. Sections of SiC composite tube were subjected to a modified expansion-due-to-compression (EDC) test in an X-ray computed tomography microscope: a polyurethane plug pressed surrogate Al 2 O 3 into the inner walls of the SiC/SiC composite tubes to achieve hard contact. A pure EDC test with just a polyurethane plug was also performed as a reference. Through the use of displacement fields, digital volume correlation revealed inhomogeneous deformation fields in the tubes, even for pure EDC, which was related to the inherent defects in the structure. Deep learning–aided segmentation and systematic data analysis revealed that the presence of inhomogeneous deformation applied by the hard contact was exaggerated by the presence of inner surface imperfections left behind from the matrix densification process. In conclusion, the findings provide insights into the applications, highlighting the necessity for improvements in inner surface roughness and the incorporation of localized contacts in pellet–cladding mechanical interaction computational models.

Composites↗
DOE OSTI2020

Gradient microstructure induced shear band constraint, delocalization, and delayed failure in CuZr nanoglasses

The mechanical properties of metallic glasses (MGs) can be significantly tuned by introducing a nanoscale glass-glass interface microstructure. Here, we design three types of Cu 64 Zr 36 MG seamless gradient microstructures by combining glassy grain sizes from 3 to 15 nm. We perform tensile loading molecular dynamics simulations on the named gradient nanoglasses to characterize their mechanical behavior. In all cases, results indicate the generation of gradient plasticity following the gradient in grain size, i.e. local plasticity increases from large to small grain size regions. Loading parallel to the gradient direction results in initial broad necking followed by catastrophic failure. In contrast, loading perpendicular to the gradient direction results in diffused shear band propagation from large to small grain size regions, delaying the generation of a dominant shear band and further delocalizing plastic deformation. In conclusion, the results demonstrate the synergistic effects generated by heterogeneous gradient designs in the mechanical behavior of metallic glasses.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Characteristics of Premature Creep Failure in Over-tempered Base Metal of Grade 91 Steel Weldment

Characteristics of premature creep failure in the over-tempered base metal (OT-BM) of a Grade 91 steel weldment are investigated with specially designed creep experiments and advanced microstructure characterization. In situ digital image correlation (DIC) strain measurements reveal that local creep strain as high as 100% accumulated in the OT-BM, compared with only 10% nominal strain over the gauge length. The creep strain rate in the OT-BM is identical to that in the intercritical heat-affected zone and fine-grained heat-affected zone at the secondary creep stage and early tertiary stage, but faster at the late tertiary stage. Microstructural analysis shows that highly recovered microstructure in the OT-BM leads to the lowest hardness, the largest grain size, the lowest fraction of coincidence site lattice boundaries, and the lowest localized strain energy. Dislocation creep and transgranular creep fracture are the dominant deformation and fracture mechanisms in the OT-BM under the current creep testing condition of a low temperature (550 °C) and a high stress (215 MPa).

42 ENGINEERING↗
DOE OSTI2013

Larger Maximum Tumor Diameter at Radical Prostatectomy Is Associated With Increased Biochemical Failure, Metastasis, and Death From Prostate Cancer After Salvage Radiation for Prostate Cancer

Purpose: To investigate the maximum tumor diameter (MTD) of the dominant prostate cancer nodule in the radical prostatectomy specimen as a prognostic factor for outcome in patients treated with salvage external beam radiation therapy (SRT) for a rising prostate-specific antigen (PSA) value after radical prostatectomy. Methods and Materials: From an institutional cohort of 575 patients treated with SRT, data on MTD were retrospectively collected. The impact of MTD on biochemical failure (BF), metastasis, and prostate cancer-specific mortality (PCSM) was assessed on univariate and multivariate analysis using Kaplan-Meier and Cox proportional hazards models. Results: In the 173 patients with MTD data available, median follow-up was 77 months (interquartile range, 47-104 months) after SRT, and median MTD was 18 mm (interquartile range, 13-22 mm). Increasing MTD correlated with increasing pT stage, Gleason score, presence of seminal vesicle invasion, and lymph node invasion. Receiver operating characteristic curve analysis identified MTD of >14 mm to be the optimal cut-point. On univariate analysis, MTD >14 mm was associated with an increased risk of BF (P=.02, hazard ratio [HR] 1.8, 95% confidence interval [CI] 1.2-2.8), metastasis (P=.002, HR 4.0, 95% CI 2.1-7.5), and PCSM (P=.02, HR 8.0, 95% CI 2.9-21.8). On multivariate analysis MTD >14 mm remained associated with increased BF (P=.02, HR 1.9, 95% CI 1.1-3.2), metastasis (P=.02, HR 3.4, 95% CI 1.2-9.2), and PCSM (P=.05, HR 9.7, 95% CI 1.0-92.4), independent of extracapsular extension, seminal vesicle invasion, positive surgical margins, pre-RT PSA value, Gleason score, and pre-RT PSA doubling time. Conclusions: For patients treated with SRT for a rising PSA value after prostatectomy, MTD at time of radical prostatectomy is independently associated with BF, metastasis, and PCSM. Maximum tumor diameter should be incorporated into clinical decision making and future clinical risk assessment tools for those patients receiving SRT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2014

Genomic Prostate Cancer Classifier Predicts Biochemical Failure and Metastases in Patients After Postoperative Radiation Therapy

Purpose: To test the hypothesis that a genomic classifier (GC) would predict biochemical failure (BF) and distant metastasis (DM) in men receiving radiation therapy (RT) after radical prostatectomy (RP). Methods and Materials: Among patients who underwent post-RP RT, 139 were identified for pT3 or positive margin, who did not receive neoadjuvant hormones and had paraffin-embedded specimens. Ribonucleic acid was extracted from the highest Gleason grade focus and applied to a high-density-oligonucleotide microarray. Receiver operating characteristic, calibration, cumulative incidence, and Cox regression analyses were performed to assess GC performance for predicting BF and DM after post-RP RT in comparison with clinical nomograms. Results: The area under the receiver operating characteristic curve of the Stephenson model was 0.70 for both BF and DM, with addition of GC significantly improving area under the receiver operating characteristic curve to 0.78 and 0.80, respectively. Stratified by GC risk groups, 8-year cumulative incidence was 21%, 48%, and 81% for BF (P<.0001) and for DM was 0, 12%, and 17% (P=.032) for low, intermediate, and high GC, respectively. In multivariable analysis, patients with high GC had a hazard ratio of 8.1 and 14.3 for BF and DM. In patients with intermediate or high GC, those irradiated with undetectable prostate-specific antigen (PSA ≤0.2 ng/mL) had median BF survival of >8 years, compared with <4 years for patients with detectable PSA (>0.2 ng/mL) before initiation of RT. At 8 years, the DM cumulative incidence for patients with high GC and RT with undetectable PSA was 3%, compared with 23% with detectable PSA (P=.03). No outcome differences were observed for low GC between the treatment groups. Conclusion: The GC predicted BF and metastasis after post-RP irradiation. Patients with lower GC risk may benefit from delayed RT, as opposed to those with higher GC; however, this needs prospective validation. Genomic-based models may be useful for improved decision-making for treatment of high-risk prostate cancer.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Safety and Palliative Efficacy of Single-Dose 8-Gy Reirradiation for Painful Local Failure in Patients With Stage IV Non-Small Cell Lung Cancer Previously Treated With Radical Chemoradiation Therapy

Purpose: To investigate the safety and efficacy of single-dose 8-Gy palliative chest reirradiation (CRI) in metastatic non-small cell lung cancer (M-NSCLC) patients with painful thoracic failures (TF) within the previous radiation portal. Patients and Methods: We retrospectively analyzed the clinical data of 78 M-NSCLC patients who received single-dose 8-Gy CRI for painful TF after concurrent chemoradiation therapy to a total radiation dose of 52 to 66 Gy between 2007 and 2012. Primary endpoints included significant pain relief (SPR) defined as a ≥2 point decrement in the Visual Analogue Scale for Pain inventory (VAS-P), time to pain relief, and duration of pain control. Secondary objectives were survival and prognostic factors. Results: Treatment was well tolerated, with only 5.1% grade 3 pneumonitis and 1.3% grade 2 esophagitis. Pre-CRI median and post-CRI minimum VAS-P were 7 and 3 (P<.001), respectively. SPR was noted in 67 (85.9%) patients, and only 3 (3.9%) scored progressive pain. Median time to lowest VAS-P and duration of pain control were 27 days and 6.1 months, respectively. Median overall survival (OS) was 7.7 months, and the 1-year OS rate was 26.5%. On multivariate analyses, lower Eastern Cooperative Oncology group score (1-2; P<.001), absence of anemia (P=.001), and fewer metastatic sites (1-2; P<.001) were found to be associated with longer OS. Conclusions: Single-dose 8-Gy CRI provides safe, effective, and durable pain palliation for TF in radically irradiated M-NSCLC patients. Because of its convenience, lower cost, and higher comfort, the present protocol can be considered an appropriate option for patients with limited life spans.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Colorectal Histology Is Associated With an Increased Risk of Local Failure in Lung Metastases Treated With Stereotactic Ablative Radiation Therapy

Purpose: Stereotactic ablative radiation therapy (SABR) is increasingly used to treat lung oligometastases. We set out to determine the safety and efficacy of this approach and to identify factors associated with outcomes. Methods and Materials: We conducted a retrospective study of patients treated with SABR for metastatic lung tumors at our institution from 2003 to 2014. We assessed the association between various patient and treatment factors with local failure (LF), progression, subsequent treatment, systemic treatment, and overall survival (OS), using univariate and multivariate analyses. Results: We identified 122 tumors in 77 patients meeting inclusion criteria for this study. Median follow-up was 22 months. The 12- and 24-month cumulative incidence rates of LF were 8.7% and 16.2%, respectively; the 24-month cumulative incidence rates of progression, subsequent treatment, and subsequent systemic treatment were 75.2%, 64.5%, and 35.1%, respectively. Twenty-four-month OS was 74.6%, and median OS was 36 months. Colorectal metastases had a significantly higher cumulative incidence of LF at 12 and 24 months (25.5% and 42.2%, respectively), than all other histologies (4.4% and 9.9%, respectively; P<.0004). The 24-month cumulative incidences of LF for colorectal metastases treated with a biologically effective dose at α/β = 10 (BED{sub 10}) of <100 Gy versus BED{sub 10} of ≥100 Gy were 62.5% and 16.7%, respectively (P=.08). Toxicity was minimal, with only a single grade 3 or higher event observed. Conclusions: SABR for metastatic lung tumors appears to be safe and effective with excellent local control, treatment-free intervals, and OS. An exception is metastases from colorectal cancer, which have a high LF rate consistent with a radioresistant phenotype, suggesting a potential role for dose escalation.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2015

Competing Risk Analysis of Neurologic versus Nonneurologic Death in Patients Undergoing Radiosurgical Salvage After Whole-Brain Radiation Therapy Failure: Who Actually Dies of Their Brain Metastases?

Purpose: To estimate the hazard for neurologic (central nervous system, CNS) and nonneurologic (non-CNS) death associated with patient, treatment, and systemic disease status in patients receiving stereotactic radiosurgery after whole-brain radiation therapy (WBRT) failure, using a competing risk model. Patients and Methods: Of 757 patients, 293 experienced recurrence or new metastasis following WBRT. Univariate Cox proportional hazards regression identified covariates for consideration in the multivariate model. Competing risks multivariable regression was performed to estimate the adjusted hazard ratio (aHR) and 95% confidence interval (CI) for both CNS and non-CNS death after adjusting for patient, disease, and treatment factors. The resultant model was converted into an online calculator for ease of clinical use. Results: The cumulative incidence of CNS and non-CNS death at 6 and 12 months was 20.6% and 21.6%, and 34.4% and 35%, respectively. Patients with melanoma histology (relative to breast) (aHR 2.7, 95% CI 1.5-5.0), brainstem location (aHR 2.1, 95% CI 1.3-3.5), and number of metastases (aHR 1.09, 95% CI 1.04-1.2) had increased aHR for CNS death. Progressive systemic disease (aHR 0.55, 95% CI 0.4-0.8) and increasing lowest margin dose (aHR 0.97, 95% CI 0.9-0.99) were protective against CNS death. Patients with lung histology (aHR 1.3, 95% CI 1.1-1.9) and progressive systemic disease (aHR 2.14, 95% CI 1.5-3.0) had increased aHR for non-CNS death. Conclusion: Our nomogram provides individual estimates of neurologic death after salvage stereotactic radiosurgery for patients who have failed prior WBRT, based on histology, neuroanatomical location, age, lowest margin dose, and number of metastases after adjusting for their competing risk of death from other causes.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Predictors of Locoregional Failure and Impact on Overall Survival in Patients With Resected Exocrine Pancreatic Cancer

Purpose: Resection of exocrine pancreatic cancer is necessary for cure, but locoregional and distant relapse is common. We evaluated our institutional experience to better understand risk factors for locoregional failure (LRF) and its impact on overall survival (OS). Methods and Materials: We reviewed 1051 consecutive patients with nonmetastatic exocrine pancreatic cancer who underwent resection at our institution between March 1987 and January 2011. Among them, 458 had adequate follow-up and evaluation for study inclusion. All patients received adjuvant chemotherapy (n=80 [17.5%]) or chemoradiation therapy (n=378 [82.5%]). Chemotherapy and chemoradiation therapy most frequently consisted of 6 cycles of gemcitabine and 50.4 Gy in 28 fractions with concurrent 5-fluorouracil, respectively. Locoregional control (LRC) and OS were estimated with the Kaplan-Meier method. Univariate and multivariate analyses were performed with Cox proportional hazards regression models incorporating propensity score. Results: Median patient age was 64.5 years (range: 29-88 years). Median follow-up for living patients was 84 months (range: 6-300 months). Extent of resection was R0 (83.8%) or R1 (16.2%). Overall crude incidence of LRF was 17% (n=79). The 5-year LRC for patients with and without radiation therapy was 80% and 68%, respectively (P=.003; hazard ratio [HR]: 0.45; 95% confidence interval [CI]: 0.28-0.76). Multivariate analysis, incorporating propensity score, indicated radiation therapy (P<.0001; HR: 0.23; 95% CI: 0.12-0.42) and positive lymph node ratio of ≥0.2 (P=.02; HR: 1.78; 95% CI: 1.10-2.9) were associated with LRC. In addition, LRF was associated with worse OS (P<.0001; HR: 5.0; 95% CI: 3.9-6.3). Conclusions: In our analysis of 458 patients with resected pancreatic cancer, positive lymph node ratio of ≥0.2 and no adjuvant chemoradiation therapy were associated with increased LRF risk. LRF was associated with poor OS. Radiation therapy should be considered as adjuvant locoregional treatment following pancreatic cancer resection.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Validating a Local Failure Risk Stratification for Use in Prospective Studies of Adjuvant Radiation Therapy for Bladder Cancer

Purpose: To inform prospective trials of adjuvant radiation therapy (adj-RT) for bladder cancer after radical cystectomy, a locoregional failure (LF) risk stratification was proposed. This stratification was developed and validated using surgical databases that may not reflect the outcomes expected in prospective trials. Our purpose was to assess sources of bias that may affect the stratification model's validity or alter the LF risk estimates for each subgroup: time bias due to evolving surgical techniques; trial accrual bias due to inclusion of patients who would be ineligible for adj-RT trials because of early disease progression, death, or loss to follow-up shortly after cystectomy; bias due to different statistical methods to estimate LF; and subgrouping bias due to different definitions of the LF subgroups. Methods and Materials: The LF risk stratification was developed using a single-institution cohort (n=442, 1990-2008) and the multi-institutional SWOG 8710 cohort (n=264, 1987-1998) treated with radical cystectomy with or without chemotherapy. We evaluated the sensitivity of the stratification to sources of bias using Fine-Gray regression and Kaplan-Meier analyses. Results: Year of radical cystectomy was not associated with LF risk on univariate or multivariate analysis after controlling for risk group. By use of more stringent inclusion criteria, 26 SWOG patients (10%) and 60 patients from the single-institution cohort (14%) were excluded. Analysis of the remaining patients confirmed 3 subgroups with significantly different LF risks with 3-year rates of 7%, 17%, and 36%, respectively (P<.01), nearly identical to the rates without correcting for trial accrual bias. Kaplan-Meier techniques estimated higher subgroup LF rates than competing risk analysis. The subgroup definitions used in the NRG-GU001 adj-RT trial were validated. Conclusions: These sources of bias did not invalidate the LF risk stratification or substantially change the model's LF estimates.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2016

Patterns and Timing of Failure for Diffuse Large B-Cell Lymphoma After Initial Therapy in a Cohort Who Underwent Autologous Bone Marrow Transplantation for Relapse

Purpose: To evaluate the location and timing of initial recurrence in patients with diffuse large B-cell lymphoma (DLBCL) who subsequently underwent high-dose chemotherapy with autologous stem cell transplant (HDC/ASCT), to direct approaches for disease surveillance, elucidate the patterns of failure of contemporary treatment strategies, and guide adjuvant treatment decisions. Methods and Materials: We analyzed consecutive patients with DLBCL who underwent HDC/ASCT between May 1992 and March 2014 at our institution. Of the 187 evaluable patients, 8 had incomplete data, and 79 underwent HDC/ASCT as a component of initial treatment for de novo or refractory DLBCL and were excluded from further analysis. Results: The median age was 50.8 years; the median time to relapse was 1.3 years. Patients were segregated according to the initial stage at diagnosis, with early stage (ES) defined as stage I/II and advanced stage (AS) defined as stage III/IV. In total, 40.4% of the ES and 75.5% of the AS patients relapsed in sites of initial disease; 68.4% of those with ES disease and 75.0% of those with AS disease relapsed in sites of initial disease only. Extranodal relapses were common (44.7% in ES and 35.9% in AS) and occurred in a variety of organs, although gastrointestinal tract/liver (n=12) was most frequent. Conclusions: Most patients with DLBCL who relapse and subsequently undergo HDC/ASCT initially recur in the previously involved disease site(s). Time to recurrence is brief, suggesting that frequency of screening is most justifiably greatest in the early posttherapy years. © 2016 Elsevier Inc.

62 RADIOLOGY AND NUCLEAR MEDICINE↗