Residual Mismatch Research Articles

Measurement of Prostate Inter-Fraction Movement by Tracking Implanted Fiducials in Daily CBCT Projections

To develop a method for accurately determining implanted fiducial locations in 3D using template matching and sequential stereo in CBCT projection data. This technique will be used in both retrospective studies to improve motion models and to improve fiducial tracking during treatment for motion management. During planning each fiducial is contoured individually. Using non-clinical research software, a separate template is generated from the planning CT for each fiducial. In offline mode each fiducial is tracked in the CBCT projections by template matching followed by sequential stereo. In the offline mode the full scan data is available so the sequential stereo is applied in retrospective analysis mode (as opposed to real-time tracking), and by iteration outliers are removed. The match score threshold used for accepting 2D matches is initially set to a high value and reduced incrementally until a minimum of 100 trajectory points (out of > 900 projections) are produced with a range of motion below a threshold. The estimated 3D location is taken as the average of results from these trajectory points. Horn’s method for absolute orientation using unit quaternions is used to determine the 3D translation and rotation of the fiducials from the planning CT scan to the CBCT. Results from a prostate patient, with 3 implanted fiducials and 9 treatment CBCTs are shown here. The tracked fiducial locations were overlaid on the CBCT scan and evaluated by an observer. No failed detections were identified in this preliminary dataset. The recorded prostate motion was random over the course of treatment, with no clear temporal trends. The largest translations were in the Z (P-A) direction and rotations about the X (L-R) axis. Amplitude of motions were within expected range. The residual mismatch in fiducial positions after rigid 3D transformation was on the order of the voxel size, or less. CBCT projection images can be used directly for 3D fiducial localization. Further analysis is being carried out, but the technique may benefit from not being limited by the CBCT voxel size, not influenced by CBCT reconstruction artifacts and more robust to motion. The technique can be used in both retrospective applications, where projections are archived, and online for motion management.Tabled 1Abstract 2732; TableDays Post SimulationTranslation IEC (mm)Rotation IEC isocenter (deg)TxTyTzRxRyRz13-0.042.17-3.1412.02.72.316-0.67-0.20-0.435.13.80.9300.322.25-8.3124.01.81.7370.600.25-0.196.82.81.7442.710.32-0.097.42.52.6510.701.86-6.2720.04.43.851-0.57-4.064.21-15.53.4-2.061-0.622.98-6.2821.24.42.864-1.642.892.248.35.40.4Mean0.090.94-2.039.933.461.57Range-1.6, 2.7-4.1, 3.0-8.3, 4.2-15.5, 241.8, 5.4-2.0, 3.8 Open table in a new tab

How do spinopelvic parameters influence patient-reported outcome measurements after lumbar decompression?

Spinopelvic parameters indicative of sagittal imbalance include a pelvic tilt (PT) greater than 20° and a mismatch between pelvic incidence (PI) and lumbar lordosis (LL) greater than 10°. However, unlike in fusion surgery, the relationship between spinopelvic parameters and patient-reported outcome measurements (PROMs) in patients undergoing lumbar decompression surgery for neurologic symptoms is less clear. To determine whether PROMs are affected by the amount of residual (postoperative) PI-LL mismatch or PT in patients undergoing one- to three-level lumbar decompression surgeries. Retrospective cohort study (Level of Evidence: III). Patients undergoing between one to three levels of lumbar decompression surgery at a single, academic institution. PROMs-including the PCS-12, MCS-12, ODI, and VAS Back and Leg pain scores-and radiographic measurements of spinopelvic parameters. Patients were separated into groups based on a postoperative PI-LL mismatch of ≤10° or >10° and a postoperative PT<20° or ≥20°. Absolute PROM scores, the recovery ratio (RR) and the percentage of patients achieving Minimum Clinically Important Difference between groups were compared and a multiple linear regression analysis was performed. A total of 167 patients were included, with 27 patients in the PI-LL>10° group and 91 patients in the PT≥20° group. All groups exhibited significant improvement after surgery for each PROM included (p<.05) except for MCS-12 scores in the PI-LL≤10° group and both PT groups. Comparing between groups, all patients were similar with respect to preoperative scores, postoperative scores, change in scores, recovery ratios, and percentage change in Minimum Clinically Important Difference, except that patients with PT≥20° had higher pre- and postoperative VAS Back scores (p=.036 and p=.024, respectively). With multiple linear regression, postoperative PI-LL>10° and PT≥20° were not significant predictors of worse outcomes for any measured PROM. Patients with postoperative measurements PI-LL>10° and PT≥20° without instability had similar PROMs at 1 year after limited lumbar decompression when compared to patients without a spinopelvic mismatch.

Postoperative pulmonary complications in robot-assisted uro-oncological surgeries: Our experience in a tertiary cancer care centre.

Postoperative pulmonary complications in robot-assisted uro-oncological surgeries: Our experience in a tertiary cancer care centre.

Interface Stress for Bidirectional Frequency Tuning of Prebuckled Vanadium Dioxide MEMS Resonators

AbstractInterface stress between structural materials and thin film coatings has a significant influence on the resonant frequency of microelectromechanical system (MEMS) resonators. In this work, the axial stress on different types of buckled bridge MEMS resonator structures is controlled through the solid‐to‐solid phase transition of a VO2 thin film coating. The devices have identical dimensions, but different buckling orientations and profiles due to the combined effect of overetching and residual thermal stress mismatch. Thermal actuation is used to tune the resonant frequency of the device, but the changes in frequency are found to be dependent on the type of buckling for the device. Thermal actuation is achieved by applying an electrical current to integrated heaters, or by uniform substrate heating. Bidirectional tunability is found when substrate heating is used, while Joule heating shows a monotonic change in frequency. This phenomenon can be attributed to the transition in boundary conditions, where the turning points are indicated by the prominent changes in buckling amplitude. In addition, devices with opposite buckling orientations exhibit different tuning behaviors which can be explained by different bending moments induced by beam stress interface modification.

70. Anterior column realignment (ACR) performed at L2-3 achieves suboptimal lumbo-pelvic realignment compared with L2 pedicle subtraction osteotomy (PSO)

BACKGROUND CONTEXT The anterior column realignment (ACR) technique is increasingly becoming popular for treating patients with flatback deformity. The degreed of correction achieved with ACR performed at L2-3 disc has not been well studied. PURPOSE The purpose of this study was to compare the degree of deformity correction and perioperative outcomes between ACR and PSO being performed at L2 for iatrogenic flatback deformity. STUDY DESIGN/SETTING Retrospective review. PATIENT SAMPLE N = 27 patients, 9 ACR and 18 PSO. The patients were matched 1:2 (ACR:PSO) based on preoperative deformity parameters. OUTCOME MEASURES Primary outcome: Lumbo-pelvic parameters (LL-PI mismatch, SVA, PT). Secondary outcomes: estimated blood loss, transfusion requirement, length of hospital stay, operative time, postoperative complication, and hospital readmission rates. METHODS Patients were identified between 2012 and 2016 who underwent revision surgery using either the PSO or ACR technique at the L2-3 level to correct sagittal deformity. Patients who underwent ACR were matched to PSO patients in a 1:2 fashion based on preoperative lumbar lordosis (LL) and lumbar lordosis pelvis incidence (LL-PI) mismatch. Patient demographics, surgical variables, pre- and postoperative radiographic parameters, and perioperative characteristics were compared between the treatment groups using t-tests, chi-square tests, and multivariable regression models. RESULTS The cohort included 27 patients; 9 ACR patients matched to 18 PSO patients. The PSO group achieved a greater degree of lumbar lordosis compared to the ACR group (31° vs 14.23°, p CONCLUSIONS PSO surgery resulted in significantly improved lumbar lordosis and sagittal alignment correction compared to the ACR group. While ACR resulted in some improvement of lumbar lordosis, it resulted in residual lumbo-pelvic mismatch compared with patients treated with PSO. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.

Channelrhodopsin-2 Function is Modulated by Residual Hydrophobic Mismatch with the Surrounding Lipid Environment

Channelrhodopsin-2 (ChR2) is a light-gated ion channel that conducts cations of multiple valencies down the electrochemical gradient. This light-gated property has made ChR2 a popular tool in the field of optogenetics, allowing for the spatial and temporal control of excitable cells with light. A central aspect of protein function is the interaction with the surrounding lipid environment. To further explore these membrane-protein interactions, we demonstrate the role of residual hydrophobic mismatch (RHM) as a mechanistically important component of ChR2 function. We combined computational and functional experiments to understand how RHM between the lipid environment and ChR2 alters the structural and biophysical properties of the channel. Analysis of our results revealed significant RHM at the intracellular/lipid interface of ChR2 from a triad of residues. The resulting energy penalty is substantial and can be lowered via mutagenesis to evaluate the functional effects of this change in lipid-protein interaction energy. The experimental measurement of channel stability, conductance and selectivity resulting from the reduction of the RHM energy penalty showed changes in progressive H+ permeability, kinetics and open-state stability, suggesting how the modulation of ChR2 by the surrounding lipid membrane can play an important biological role and contribute to the design of targeted optogenetic constructs for specific cell types.

968. Managing Invasive Aspergillosis in the Era of Diagnostic PCR and Increasing Triazole Resistance: A Modeling Study of Different Strategies

BackgroundTriazole resistance in Aspergillus spp. is emerging and complicates prophylaxis and treatment of invasive Aspergillosis (IA) worldwide. New polymerase chain reaction (PCR) tests on broncho-alveolar lavage (BAL) fluid allow for detection of triazole resistance on a genetic level, which opened up new possibilities for targeted therapy. In the absence of clinical trials, a modeling study delivers estimates of the added value of resistance detection with PCR and which empiric therapy would be optimal when local resistance rates are known.MethodsWe performed a decision-analytic modeling study based on epidemiological data of IA, extended with estimated dynamics of resistance rates and treatment effectiveness. We compared 6 clinical strategies that differ in the use of PCR diagnostics (A: not used, B: used) and in empiric therapeutic choice in case of unknown triazole susceptibility: Voriconazole (1, VOR), Liposomal Amphotericin B (2, LAmB), or both (3). Outcome measures were proportion of correct treatment, survival, and serious adverse events.ResultsImplementing Aspergillus PCR tests was projected to result in residual treatment susceptibility mismatches of <5% for a triazole resistance rate up to 20% (using VOR). Empiric LAmB outperformed VOR at resistance rates higher than 5–20%, depending on PCR use and estimated survival benefits of VOR over LAmB (Figure 1). Combination therapy of VOR and LAmB performed best at all resistance rates but the advantage over the other strategies should be weighed against the expected increased number of drug-related serious adverse events (Figure 2). The advantage of combination therapy over LAmB monotherapy became smaller at higher triazole-resistance rates.ConclusionIntroduction of current Aspergillus PCR tests on BAL-fluid is an effective way to increase the proportion of patients that receive targeted therapy for IA. The results indicate that close monitoring of background resistance rates and of adverse drug events are important to attain the potential benefits of LAmB. The choice of strategy ultimately depends on the probability of triazole resistance, the availability of PCR, and individual patient characteristics. Disclosures All authors: No reported disclosures.

Managing invasive aspergillosis in haematological patients in the era of resistance polymerase chain reaction and increasing triazole resistance: A modelling study of different strategies

Triazole resistance in Aspergillus spp. is emerging and complicates prophylaxis and treatment of invasive aspergillosis (IA) worldwide. New polymerase chain reaction (PCR) tests on broncho-alveolar lavage (BAL) fluid allow for detection of triazole resistance at a genetic level, which has opened up new possibilities for targeted therapy. In the absence of clinical trials, a modelling study delivers estimates of the added value of resistance detection with PCR, and which empiric therapy would be optimal when local resistance rates are known. A decision-analytic modelling study was performed based on epidemiological data of IA, extended with estimated dynamics of resistance rates and treatment effectiveness. Six clinical strategies were compared that differ in use of PCR diagnostics (used vs not used) and in empiric therapeutic choice in case of unknown triazole susceptibility: voriconazole, liposomal amphotericin B (LAmB) or both. Outcome measures were proportion of correct treatment, survival and serious adverse events. Implementing aspergillus PCR tests was projected to result in residual treatment-susceptibility mismatches of <5% for a triazole resistance rate up to 20% (using voriconazole). Empiric LAmB outperformed voriconazole at resistance rates >5-20%, depending on PCR use and estimated survival benefits of voriconazole over LAmB. Combination therapy of voriconazole and LAmB performed best at all resistance rates, but the advantage over the other strategies should be weighed against the expected increased number of drug-related serious adverse events. The advantage of combination therapy over LAmB monotherapy became smaller at higher triazole resistance rates. Introduction of current aspergillus PCR tests on BAL fluid is an effective way to increase the proportion of patients that receive targeted therapy for IA. The results indicate that close monitoring of background resistance rates and adverse drug events are important to attain the potential benefits of LAmB. The choice of strategy ultimately depends on the probability of triazole resistance, the availability of PCR and individual patient characteristics.

Distributed Massive MIMO Systems With Non-Reciprocal Channels: Impacts and Robust Beamforming

Hardware calibration is essential to restore the uplink/downlink channel reciprocity for multi-user massive multiple-input multiple-output (MIMO) systems operating in a time division duplexing mode. Unfortunately, due to the associated overhead, calibration cannot be performed frequently; furthermore, any calibration procedure leaves behind a residual mismatch between the uplink and downlink channels. In this paper, we study the effects of these calibration errors on the achievable rates in the downlink of a multi-cell, multi-user, and distributed massive MIMO system. Specifically, we develop accurate, yet simple, lower-bounds on the per-user achievable rate, assuming either zero-forcing (ZF) or matched filtering (MF) are used. We also introduce a performance loss coefficient as a measure of sensitivity of the performance to the calibration errors. Using this measure, we identify the conditions under which ZF precoding is more sensitive to calibration errors than MF. Finally, we consider the robust weighted sum-rate maximization problem to mitigate the degrading effects of non-ideal calibration. Our numerical experiments show that the rate lower-bounds developed in this paper accurately quantify the impacts of non-ideal calibration on performance. Also, the proposed robust beamforming scheme improves the average sum-rate by up to 42% compared with the other available schemes.

Receiver IQ mismatch and phase noise suppression in PDM CO-OFDM system

Abstract Receiver in-phase/quadrature (IQ) mismatch as well as phase noise are hard to mitigate at the receiver in polarization division multiplexed (PDM) coherent optical orthogonal frequency division multiplexing (CO-OFDM) system and so far this problem hasn’t been properly solved yet. In this paper, a novel scheme is proposed to suppress receiver IQ mismatch and phase noise. In this scheme, through combining the pilot structure with Gram Schmidt orthogonalization procedure (GSOP) algorithm we can estimate the phase noise as well as channel distortion and eliminate the effect of part of the residual IQ mismatch. Numerical simulation shows that the proposed method has better performance than compared method at 100 Gb/s after 480 km transmission. What’s more, the calculation complexity is also analyzed.

Vertical, Horizontal and Residual Skills Mismatch in the Australian Graduate Labour Market

Studies of the Australian graduate labour market have found a substantial incidence of, and significant earnings effects from, vertical mismatch. This study extends the literature by examining horizontal mismatch, an important dimension of mismatch in its own right and which has been less studied. Over a quarter of Australian graduates are found to be mismatched, although the incidence is reduced in the longer term. Graduates from fields of study which are more occupation‐specific were found to be less likely to be mismatched. Earnings penalties were found for all forms of mismatch, and affected both general and specific fields of study.

Zero TE-based pseudo-CT image conversion in the head and its application in PET/MR attenuation correction and MR-guided radiation therapy planning.

To describe a method for converting Zero TE (ZTE) MR images into X-ray attenuation information in the form of pseudo-CT images and demonstrate its performance for (1) attenuation correction (AC) in PET/MR and (2) dose planning in MR-guided radiation therapy planning (RTP). Proton density-weighted ZTE images were acquired as input for MR-based pseudo-CT conversion, providing (1) efficient capture of short-lived bone signals, (2) flat soft-tissue contrast, and (3) fast and robust 3D MR imaging. After bias correction and normalization, the images were segmented into bone, soft-tissue, and air by means of thresholding and morphological refinements. Fixed Hounsfield replacement values were assigned for air (-1000 HU) and soft-tissue (+42 HU), whereas continuous linear mapping was used for bone. The obtained ZTE-derived pseudo-CT images accurately resembled the true CT images (i.e., Dice coefficient for bone overlap of 0.73 ± 0.08 and mean absolute error of 123 ± 25 HU evaluated over the whole head, including errors from residual registration mismatches in the neck and mouth regions). The linear bone mapping accounted for bone density variations. Averaged across five patients, ZTE-based AC demonstrated a PET error of -0.04 ± 1.68% relative to CT-based AC. Similarly, for RTP assessed in eight patients, the absolute dose difference over the target volume was found to be 0.23 ± 0.42%. The described method enables MR to pseudo-CT image conversion for the head in an accurate, robust, and fast manner without relying on anatomical prior knowledge. Potential applications include PET/MR-AC, and MR-guided RTP.

New UAV image registration method based on geometric constrained belief propagation

Image registration is a crucial step in the field of computer vision. However, the traditional scale invariant feature transform (SIFT) based method often suffers from many mismatches when being utilized to register unmanned aerial vehicle (UAV) images with obvious rotation, viewpoint change and similar textures. In order to tackle this problem, we formulate the image matching problem as a Markov Random Field (MRF) energy minimization problem and propose an accurate and fast image registration framework. First, a SIFT algorithm is utilized to extract keypoints and an algorithm called “Center of Mass” (CoM) is exploited to assign a single orientation for every point instead of SIFT since SIFT may cause ambiguity in subsequent process; second, based on the local adjacent spatial relationship between a feature point and its neighboring points, a new concept of local spatial constraints is proposed to characterize the geometric consistency between them and incorporated into a belief propagation algorithm to obtain initial matching results; finally the residual mismatches are eliminated by the Random Sample Consensus (RANSAC) algorithm, meanwhile the transformation parameters are estimated. Experiment results demonstrate that the proposed framework can significantly enhance the registration performance in UAV image registration.

An engineered opsin monomer scrambles phospholipids

The G protein-coupled receptor opsin is a phospholipid scramblase that facilitates rapid transbilayer phospholipid exchange in liposomes. The mechanism by which opsin scrambles lipids is unknown. It has been proposed that lipid translocation may occur at protein-protein interfaces of opsin dimers. To test this possibility, we rationally engineered QUAD opsin by tryptophan substitution of four lipid-facing residues in transmembrane helix 4 (TM4) that is known to be important for dimerization. Atomistic molecular dynamics simulations of wild type and QUAD opsins combined with continuum modeling revealed that the tryptophan substitutions lower the energetically unfavorable residual hydrophobic mismatch between TM4 and the membrane, reducing the drive of QUAD opsin to dimerize. We purified thermostable wild type and QUAD opsins, with or without a SNAP tag for fluorescence labeling. Single molecule fluorescence measurements of purified SNAP-tagged constructs revealed that both proteins are monomers. Fluorescence-based activity assays indicated that QUAD opsin is a fully functional scramblase. However, unlike wild type opsin which dimerizes en route to insertion into phospholipid vesicles, QUAD opsin reconstitutes as a monomer. We conclude that an engineered opsin monomer can scramble phospholipids, and that the lipid-exposed face of TM4 is unlikely to contribute to transbilayer phospholipid exchange.

The division of labor in explanations of verb phrase ellipsis

In this paper, we will argue that, of the various grammatical and discourse constraints that affect acceptability in verb phrase ellipsis (VPE), only the structural parallelism constraint is unique to VPE. We outline (previously noted) systematic problems that arise for classical structural accounts of VPE resolution, and discuss efforts in recent research on VPE to reduce explanations of acceptability in VPE to general well-formedness constraints at the level of information structure (e.g. Kehler in Linguist Philos 23(6):533–575, 2000; Coherence, reference and the theory of grammar, CSLI Publications, Stanford, 2002; Proceedings of semantics and linguistic theory, vol 25, 2015; Kertz in Language 89(3):390–428, 2013). In two magnitude estimation experiments, we show that—in line with Kehler’s predictions—degradation due to structural mismatch is modulated by coherence relation. On the other hand, we consistently find residual structural mismatch effects, suggesting that the interpretation of VPE is sensitive to structural features of the VPE antecedent. We propose that a structural constraint licenses VPE, but that sentences violating this constraint can nevertheless be interpreted. The variability in acceptability is accounted for not by additional constraints on VPE in the grammar, but by the numerous general biases that affect sentence and discourse well-formedness, such as information structural constraints (as proposed by Kertz 2013), discourse coherence relations (Kehler 2000), sensitivity to Question Under Discussion structure (e.g. Ginzburg and Sag in English interrogative constructions, CSLI Publications, Stanford, 2000; Kehler 2015), and thematic role bias at the lexical level (e.g. McRae et al. in J Mem Lang 38:283–312, 1998). We test the prediction that thematic role bias (Experiment 3) and QUD structure (Experiment 4) will influence both elliptical and non-elliptical sentences alike, while structural mismatch continues to degrade elliptical sentences alone. Our proposal differs from existing proposals in cutting the explanatory pie in a different way with respect to how variations in acceptability are accounted for. We suggest that degradation can result from at least two distinct and separable sources: violating construction-specific grammatical constraints, or from complexity differences in interpretation related to very general discourse level information.

Effect of HLA Matching on Pediatric Renal Transplant Graft Survival in China

IntroductionKidney transplantation (KTX) has become one of the most effective therapies of choice for pediatric patients with end-stage renal disease (ESRD). The extent to which HLA mismatching influences graft survival following KTX has not been clarified. Patients and MethodsThe effect of HLA amino acid residue matching on graft survival was assessed in 36 pediatric patients in whom complete donor-recipient HLA data were available. HLA-A, -B, -DR and HLA-A+B+DR loci residue mismatches were separately analyzed. ResultsHLA-A, -B, -DR residue mismatches showed no significant statistical differences on kidney graft survival probability. When analyzing HLA-A+B+DR loci residue mismatches, the presence of 3 to 4 residue mismatches significantly increased the relative risk of graft rejection (P = .0292).

NMR line shape of Si29 in single-crystal silicon

We report measurements of the NMR lineshape of 4.685\% abundant $^{29}$Si in single-crystal silicon for four different crystallographic orientations relative to the applied magnetic field. To avoid significant inhomogeneous broadening, the sample crystals are immersed in a susceptibility matched liquid and the proton NMR lineshape in the liquid is used to measure the residual susceptibility mismatch and to shim the applied field. The observed lineshapes are in good agreement with disorder-averaged spin dynamics simulations performed on a $4 \times 4 \times 4$ unit cell lattice with periodic boundary conditions. The splitting of resolved doublet features is used to measure the asymmetry $\Delta J$ of the nearest-neighbor indirect dipole or J-coupling tensor, with the result $\Delta J=90\pm20$ Hz. All resolved doublets can be identified with specific nearest and next-nearest neighbor isolated spin pairs that occur in the disorder ensemble.

Inference of direct and multistep effective connectivities from functional connectivity of the brain and of relationships to cortical geometry

BackgroundThe problem of inferring effective brain connectivity from functional connectivity is under active investigation, and connectivity via multistep paths is poorly understood. New methodA method is presented to calculate the direct effective connection matrix (deCM), which embodies direct connection strengths between brain regions, from functional CMs (fCMs) by minimizing the difference between an experimental fCM and one calculated via neural field theory from an ansatz deCM based on an experimental anatomical CM. ResultsThe best match between fCMs occurs close to a critical point, consistent with independent published stability estimates. Residual mismatch between fCMs is identified to be largely due to interhemispheric connections that are poorly estimated in an initial ansatz deCM due to experimental limitations; improved ansatzes substantially reduce the mismatch and enable interhemispheric connections to be estimated. Various levels of significant multistep connections are then imaged via the neural field theory (NFT) result that these correspond to powers of the deCM; these are shown to be predictable from geometric distances between regions. Comparison with existing methodsThis method gives insight into direct and multistep effective connectivity from fCMs and relating to physiology and brain geometry. This contrasts with other methods, which progressively adjust connections without an overarching physiologically based framework to deal with multistep or poorly estimated connections. ConclusionsdeCMs can be usefully estimated using this method and the results enable multistep connections to be investigated systematically.

Repositionnement par le système ExacTrac® pour l’irradiation sans cadre invasif de métastases cérébrales en conditions stéréotaxiques : étude descriptive de cinq centres français

PurposeThis study aimed to analyse the positioning protocols with the ExacTrac® system, associated with a dedicated linear accelerator such as Novalis®, for stereotactic treatment of brain metastases in several French centres. Materials and methodsA survey, including three questions about the prescription of irradiation and twenty-one questions about how the ExacTrac® system is used, was sent to nine French centres owning a dedicated Novalis® accelerator. Five centres have accepted to participate in the study. ResultsAll centres checked the positioning before each treatment's bow, with residual mismatch tolerances of 0.5 to 0.7mm for the translations and 0.5 to 1° for the rotations. All centres except one also realised orthogonal planar images of classic incidences to help operators ensure proper isocentre positioning. Prescribed doses were 20Gy in one fraction, 30Gy and 33Gy in three fractions or 34Gy in four fractions, mainly depending on the size of the lesion. Finally, a physician validated the images at the treatment station before starting the irradiation. ConclusionsThe practices of the different centres concerning the positioning protocols were rather homogeneous, in agreement with the literature data on ExacTrac® system's accuracy, as well as proposed fractionations. The systematic medical validation at the treatment station may, however, be questioned because of the waiting time between the doctor's call and validation itself and because of its usefulness; indeed, corrections by the radiation oncologist are very rare and in some centres, non-existent.

Crack path selection at the interface of wrought and wire + arc additive manufactured Ti–6Al–4V

Crack propagation deviation tendency in specimens containing an interface between wrought alloy substrate and Wire+Arc Additive Manufacture (WAAM) built Ti–6Al–4V is investigated from the viewpoints of microstructure, residual stress and bi-material system. It is found that a crack initiated at the interface tends to grow into the substrate that has equiaxed microstructure and lower resistance to fatigue crack propagation. Experimental observations are interpreted by finite element modelling of the effects of residual stress and mechanical property mismatch between the WAAM and wrought alloy. Residual stresses retained in the compact tension specimens are evaluated based on measured residual stress in the initial WAAM built wall. Cracks perpendicular to the interface kept a straight path owing to the symmetrical residual stress distribution. In this case the tangential stress in bi-material model is also symmetric and has the maximum value at the initial crack plane. In contrast, cracks parallel to the interface are inclined to grow towards the substrate due to the mode II (or sliding mode) stress intensity factor caused by the asymmetric residual stress field. Asymmetric tangential stress in the bi-material model also contributes to the observed crack deviation trend according to the maximum tangential stress criterion.