The influence of an aortic aneurysm on blood flow waveforms is well established, but how to exploit this link for diagnostic purposes still remains challenging. This work uses a combination of experimental and computational modelling to study how aneurysms of various size affect the waveforms. Experimental studies are carried out on fusiform-type aneurysm models, and a comparison of results with those from a one-dimensional fluid–structure interaction model shows close agreement. Further mathematical analysis of these results allows the definition of several indicators that characterize the impact of an aneurysm on waveforms. These indicators are then further studied in a computational model of a systemic blood flow network. This demonstrates the methods’ ability to detect the location and severity of an aortic aneurysm through the analysis of flow waveforms in clinically accessible locations. Therefore, the proposed methodology shows a high potential for non-invasive aneurysm detectors/monitors. Cardiovascular disease is responsible for the death of over eight million people worldwide every year. Among these deaths, aortic aneurysms alone are responsible for more than 100,000 deaths, with about 6000 occurring in England and Wales as a result of rupture. An aortic aneurysm is a dilation of the aorta, usually exceeding the normal diameter by more than 50%. The abdominal aortic aneurysm (AAA) is the most prevalent type of aortic aneurysm, and it is often asymptomatic. As it increases in size, the aneurysm is more likely to rupture and becomes a life-threatening condition. The symptoms are rarely noticed before rupture of the aneurysm, which prompted the healthcare systems to investigate various screening programs based on ultrasound and MRI. A Multicentre Aneurysm Screening Study (MASS) was one of the first large screening programmes for AAA in the UK. The results from the MASS programme showed that detection of AAA reduced risk of death in a 4-year period from 0.33 to 0.19% , especially in overweight people . SymptoIn a clinical setting, ultrasound (US) is currently the most practical, non-invasive and inexpensive modality in screening for and surveillance of AAA, with a sensitivity and specificity of more than 98% , which was inserted into the tube through a Y-junction at the inlet of the tube or outlet of the tube. The flow rate was measured using ultrasound flow probes . All measurements of the pressure and flow rate are taken in tube segment 3 shown in Fig. Repeated measurements for every aneurysm in every site are taken from 8 to 15 for every combination of aneurysm size/site, resulting in more than 200 measurements overall. The basic sampling frequency is 500  Hz, but 1 kHz is also used in some measurements to ensure that pressure waveforms are properly captured. First, the measured waveforms are smoothed by convolution with a Gaussian function at a width of two time steps. As the recording is not synchronized with the pump, it is necessary to align all waveforms to start the main pulse at the same instant. Then the measured waveforms are averaged in the sample rate 500 Hz in order to decrease the influence of noise further.The averaged measured pressure waveforms are presented in Fig. t and x denote the partial derivatives with respect to time t and coordinate along the pipe x, respectively; A is the cross-sectional area of the lumen; E and A one-dimensional approximation is employed for the numerical simulation. This approximation is mainly based on Stergiopulos’s model  can can25) cn denotes the nth time step for any variable and Variables At the connections between tubes the continuity of the flow rate Most challenging is to determine the inlet conditions, i.e. the waveform produced by the pump. The wave generated by the pump can partly reflect from the aneurysm, producing a backward propagating wave, which may be reflected by the piston to form a forward propagating wave. The wave is generated only whilst the piston is in motion. Its waveform shape is determined completely by the piston velocity variation. The piston motion is subjected to load generated by the fluid resistance and motion. This load exists even in the absence of reflection (such case is considered in Appendix 2), but in the presence of the aneurysm, the reflected wave imparts an additional load on the piston motion. Thus, the generated waveform heavily depends on the aneurysm size. Note that when the piston is at rest, the backward velocity wave reflected from the aneurysm and reflected from the piston/rigid pipe should cancel each other at the point of contact. This not true, however, for the pressure. Thus, measuring the velocity waveform near the piston gives the actual piston motion. As the pipes connecting the pump and the main tube are rather rigid, the velocity close to the inlet of the main tube has almost the same velocity wave shape as that of the one generated by the piston but scaled by the piston/pipe area ratio.One can see in Fig. Therefore, the velocity waveform measured at the interval The results of the numerical simulations are shown in Fig. There are two approaches on the separation of the waveform into forward and backward travelling waves. The first approach is based on the fact that nonlinear and viscous effects are relatively small. The second is based on the water-hammer equation and is valid for finite amplitude waves  ..\documenmentclasspt{minimaNote that typically the in vivo experimental wave shapes are given in terms of up to 20 harmonic components. If the period of the main harmonic is approximately 1 s, then the wavelength of the 20th harmonic is approximately 1 m, which is greater than the length of a typical aneurysm. Such long waves can sense the aneurysm as a localized inhomogeneity (0D object) characterized by a lumped parameter: its compliance. We can therefore introduce an excess of the vessel compliance caused by the aneurysmx-coordinate is referenced from the aneurysm inlet. The cross-sectional compliance is defined asThe additional aneurysm compliance, K parameter is the ratio of the additional aneurysm compliance to that of the compliance of the healthy vessel of same length. It can easily be calculated numerically, but for the model aneurysms used in the experiment it can be calculated analytically as well by directly integrating Eq. (D) studied here. We use these values as reference ones. They are compared below with the values of K evaluated from the waveform analysis.The artificial aneurysms used in the experiments carried out are designed to have a constant wall stiffness coinciding the wall stiffness of main tube in which the aneurysm is embedded. Substituting ′hv into  we obtaimentclass2pt{minimNow we consider the wave reflection from an aneurysm by treating it as a 0D object with compliance R is the complex reflection coefficient that needs to be determined. To the right (exit), there will be a propagating wave S. Omitting the common factor R and S. Solving Eqs. (R can be written in the following formConsider an infinitely long tube and an aneurysm located at distance H(t) is the unit-step Heaviside function. This allows the computation of the reflected pulse directly in the time domain through the convolution,Applying the Fourier transform to the incident pulse iω) from , we obtaNote that the time-domain computation (despite it is much more cumbersome) has advantages over the frequency domain due to the fact that in the time domain the pulses reflected from different objects can be easily separated as they have different arrival times. In the frequency domain all the reflections are mixed together that complicates the analysis and parameter determination.K  and theThus, the proposed method allows for detecting both the aneurysm location and its compliance. The accuracy of the procedure can be seen from the comparison of reference values, which are denoted as “Refer.” in Table Now we apply the proposed method of aneurysm detection to a human arterial network that is modelled numerically. For the modelling, we use the arterial network ADAN 55 proposed in the work by Blanco et al.  and thorThe wall thickness is determined from the relation  is chosen to model the AAA. Aneurysms of two sizes are modelled: two and three times wider than the healthy vessel in its widest part. We will refer to them as AAA-2 and AAA-3, respectively. The shape is assumed to be the same as in the work by Low et al. , i.e.31\p(t), average velocity u(t) and area variation A(t) are monitored at the centre of the segments indicated in Table The flow rate entclass1pt{minimaAs seen, the presence of an aneurysm results in a pressure drop at a certain time interval after the main peak. This is particularly pronounced in the case of the AAA-3 aneurysm. The graphs clearly show the main feature of the large AAA’s presence, i.e. a pressure drop just after the main peak followed by a distinct second peak after that.We apply the proposed aneurysm detection method to the sites located in aortic segments. First, eight segments listed in Table According to Eq. , the refB is the parameter to be found. The B parameter approximates the background of the remaining reflections, noise and the forward wave pulse. A simple constant value for this parameter is sufficient here.Another challenge is that the background noise of the waves reflected from locations other than the AAA remains. Therefore, we fit the function B:T / 3 for the width of the interval gives satisfactory results in all the cases considered. Note that the procedure is more sensitive to the time interval Now we minimize the following functional with respect to the three parameters, Examples of the waveform fit for segment 19a (Aortic Arch IV) are shown in Fig. The results of function fitting for all eight monitored segments are listed in Table Finally, we consider the case that is most relevant when targeting this technology for non-invasive assessments in clinical practice, i.e. the determination of the AAA parameters by measuring the waveforms at more accessible sites such as the carotid artery. Here we will use the waveforms computed in the middle of the right common carotid (RCA) (segment 3) and left common carotid (LCA) (segment 14). This case is more complicated because the wave separation does not help, as the forward pulse and the pulse reflected from the AAA propagate in the same direction. Therefore, aneurysm detection based on the carotid waveform requires a more sophisticated approach of signal processing. The approach should be based on the possibility to calculate the shape of pulse reflected from the aneurysm and then to recognize it on the background of the main signal, other reflections and noise. Our proposed signal processing solution to this problem is described next.G is given by Eq.  waveform, filter it using n by Eq.  and fit In the case of the LCA, the time lag is the time of pulse propagation from the LCA inlet to the AAA and back. In the case of the RCA, the time lag is the duration of pulse propagation from the brachiocephalic trunk inlet  investigate waveform changes caused by aneurysms of various severity, 2) to validate our 1D computational model in the presence of aneurysms. The results obtained allow us to develop a new method of aneurysm detection based on waveform analysis. These results are then successfully employed to a numerical model of a human arterial system to evaluate the potential for detecting aneurysms. Analysis of the waveforms observed in the carotid arteries shows that aneurysms can be detected in terms of location and severity through our new method.The proposed method, which incorporates the reflected waveform computation d by Eq.  and can The aneurysm compliance given by Eq.  is a verh and its elastic modulus Note that in this work we focus on the effect of aneurysm geometries on the pulse wave reflections. Therefore, the artificial aneurysms have been produced to keep the complexities to a minimum by adapting constant thickness and stiffness. We use identical settings in the numerical simulations. If the wall thickness then Eq.  should bthen Eq. .Observe that the wall stiffness nator in . Therefointegral . Hence, One of the advantages of the proposed method is that it can be implemented in the time domain where it is easier to distinguish pulses reflected from different parts in the cardiovascular system. Another advantage is that there is no need to calculate the reflection coefficient as the pulse reflected from an aneurysm definitely changes its shape. Therefore, if we define the reflection coefficient, for example, as a ratio of peak values of reflected and incident pulses, it will depend on the shape of the incident pulse, i.e. it will not be invariant with respect to incident pulse shape and parameters. The same remark can be directed to the pulse intensity analysis28) are d


The corrected Figure In the original article, there was a mistake in Figure x and y axes were mislabeled and ⋆p-value <0.05 indicating significance was missing]. The corrected Figure In the original article, there was a mistake in Figure The original article was updated.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.


The validity of selection tests is underestimated if it is determined by simply calculating the predictor-outcome correlation found in the admitted group. This correlation is usually attenuated by two factors: (1) the combination of selection variables which can compensate for each other and (2) range restriction in predictor and outcome due to the absence of outcome measures for rejected applicants.Here we demonstrate the logic of these artifacts in a situation typical for student selection tests and compare four different methods for their correction: two formulas for the correction of direct and indirect range restriction, expectation maximization algorithm (EM) and multiple imputation by chained equations (MICE). First we show with simulated data how a realistic estimation of predictive validity could be achieved; second we apply the same methods to empirical data from one medical school.The results of the four methods are very similar except for the direct range restriction formula which underestimated validity.For practical purposes Thorndike’s case C formula is a relatively straightforward solution to the range restriction problem, provided distributional assumptions are met. With EM and MICE more precision is obtained when distributional requirements are not met, but access to a sophisticated statistical package such as R is needed. The use of true score correlation has its own problems and does not seem to provide a better correction than other methods. If the predictive validity of an admission test is low, its employment is hard to justify. Therefore a trustworthy estimation of predictive validity is needed. The predictive validity of a test is defined as the correlation of its scores with an outcome criterion. However in many test situations this correlation is not directly calculable. Here we consider two complications which lead to an underestimation of predictive validity:1. The selection decision is based on multiple criteria, which can compensate for each other. This generates a negative correlation between predictors which attenuates the predictor-outcome correlation for each of them.2. As outcome data are not available for rejected applicants the range of predictors as well as of the criterion variable is restricted and this attenuates the predictor-outcome-correlation.Both problems are often ignored or treated superficially. This seems to reflect a lack of communication between psychometric statisticians and applied researchers, who may feel deterred by the multitude of methods offered and their seemingly inscrutable subtleties . In this1 (for example an entrance test) and X2 (for example hGPA) are combined into a selection score Z = X1 + X2. Applicants are admitted according to their rank order on Z. In the following, we present artificial data generated to illustrate the scenario. We use the software R with the package MASS [1, X2, and Y from a standard normal random distribution  restricted to yield the following correlations: N = 1000 applicants).Let’s imagine a situation typical for student selection: Two selection variables Xa, incumbents with i. Examples: 1 (test) in the applicants, 1 in the incumbents after the linear effect of X2 (hGPA) has been removed from X1. X1 is the predictor of interest - we want to know how well the test performs in predicting the outcome Y independent of X2. While X1 and X2 are measured in all applicants, the outcome variable Y is only measured in the incumbents. Thus, 1 and Y in the unrestricted sample (Following the terminology of McManus  the tota1), and high school grade point average (hGPA) (X2) a low test score might be compensated by a high hGPA and vice versa. Only if both measures are low an applicant will be rejected which creates a negative correlation Here we demonstrate why compensatory selection is a factor that attenuates the estimation of predictive validity. If two measures are combined into a sum that is used for the selection decision, e.g. a test score for natural science knowledge X, and higThe negative correlation has repercussions for predictive validity: the negative correlation edictors .1 and X2 in the unrestricted sample of applicants is almost zero  can still be accepted if her entrance test result (X1) is superior. A low hGPA would predict less study success (Y), whereas a high test results would predict more study success. Thus the negative relation between the test score and hGPA would mask the predictive power of the test. This also goes vice versa, if entrance test and hGPA change places. Multiple regression removes the effect of reciprocal suppression as it shows the independent contribution of each predictor after controlling for all other predictors Multiple imputation if missing values by chained equations (MICE)We will consider four methods for correcting the effect of range restriction:1 by the residual X1•2, thus 2.Methods 2–4 handle indirect range restriction, so a correction for the effect of reciprocal suppression due to compensatory selection is not necessary. We included this analysis for clarification, not with the intention to use the semipartial correlation Thorndike’s case A formula [1 is evaluated with an outcome Y. formula  is widelLinearity. ein Y is the difference between the observed Y value and the expected value in Y that the regression model implies. Homoscedasticity requires the error varianceeto be equal for the applicants and the incumbents:Homoscedasticity. The error varianceThorndike’s case A formula depends on two assumptions :LinearitLet Then the estimation of the unrestricted correlation ion (see ) the res1 (homoscedasticity), then it does not matter at which location on the X-axis the distribution has been cut by the selection rule as long as the cut is clean and not rendered fuzzy by the involvement of a third variable such as X2.If the error variance in Y is equal at any level of X1 (indirect selection). Schmidt and Hunter [In the empirical literature Thorndike’s case A formula is often used even when selection is also guided by other variables than Xd Hunter  demonstr2. Thorndike’s case C formula for indirect selection. In our simulation we have a second selection variable X2, which is not envisaged by Thorndike’s case A formula. If multiple variables are used for selection, a compound selection variable Z is formed as a function of X1, X2, … Xk, e.g. Z = X1+ X2 + … + Xk Thorndike’s case C formula incorporates such indirect  selection based on Z, of which the variable of interest, X1, only is a part [s a part :\documenThe EM algorithm computes maximum likelihood estimates from incomplete data [ete data . It fillhe model . In a sthe model . In our he model .4. The MICE algorithm is the most recent and according to its advocates the most accurate approach [m of complete datasets are created which contain different plausible estimates of the missing values, but identical values for the observed data. In the analysis phase, each complete dataset is analyzed with conventional statistical methods. In the pooling phase the m parameter estimates are pooled into a single set of parameter estimates by calculating simply the arithmetic average of the m estimates from the analysis phase. Via multiple imputations the variance in the variables with missing values is handled more realistically than in EM. MICE is a Bayesian type of estimation. In Bayesian statistics, a prior distribution of parameter values is modified in the light of new evidence to obtain a posterior distribution of improved estimates. MICE uses Markov chain Monte Carlo (MCMC) methods to find the posterior distribution of the parameters. MCMC algorithms need a large number of steps and therefore are CPU-intensive. Only with the recent advent of powerful PCs such methods have become widely available for applied research. We use the package MICE for R [approach . The acrCE for R .N = 1000 applicants) 1000 times and varied the student selection ratio  that leads to missing data on Y for the rejected applicants. As we know r and The data shown to illustrate the issue of range restriction were used in a Monte Carlo simulation. We rerun the illustrative scenario  . The HAMThe compensatory relation between HAM-Nat and hGPA imposes a negative correlation between these predictor variables in the incumbents Fig.  by the sWe have withheld a complication in our empirical example to keep the description of correction methods as simple as possible. Actually there is a fourth variable which modifies the rank order in half of the accepted applicants according to their performance in a test of social competence . This isBeing good at natural science, a student is well equipped to understand the subject matter of the first terms in medical school. But having on average a lower hGPA, which was compensated by her or his high science test score would mean that she or he lacks some of the abilities associated with a high hGPA, presumably abilities which help to negotiate an educational system, dubbed the “academic backbone” by McManus . A less Due to reciprocal suppression the first order correlation of both variables with the outcome measure is lower than the correlation of the residuals obtained when the linear effect of hGPA is taken out of the HAM-Nat scores and vice versa Fig. . It riseThe ratio of standard deviations for the unrestricted sample relative to the restricted sample is entclass1pt{minimaThe estimations from Thorndike’s case C formula, EM and MICE and are close when used for the empirical data from the HAM-Nat Table . Therefo1 is estimated, but the operational validity which is defined as the theoretical correlation 1. The empirical correlation ryy ∣ a, is not known.An alternative approach to correct for range restriction due to indirect selection is Hunter and Schmidt’s stepwise procedure based on classical test theory . It requ1 ∣ a = 0.8 and the reliability of Y∣i = 0.7. Obviously the estimation of 1 and Y, which in turn depend on the method used, e.g. retest-reliability, split half reliability, or some coefficient of internal consistency such as Cronbach’s alpha or omega. As most methods for the estimation of reliability suffer from drawbacks [For the HAM-Nat data presented above the approach by Hunter and Schmidt yields an estimation of rawbacks , 32 the Should a correlation coefficient indicating predictive validity be corrected for attenuation by the unreliability of the test scores involved? Few researchers use such corrections, even when they otherwise adhere to classical test theory (CTT), but some advocate them, e.g. McManus et al. reporting operational validity and construct-level predictive validity , which iThe meaning of the true score for the HAM-Nat gets complicated after a little reflection. Why would scientific knowledge predict study success? Certainly because it is auspicious to enter the university with a good foundation for the curriculum of the first two years. But most probably other more basic third factors are in the game which act upon scientific knowledge as well as on study success, factors like motivation, conscientiousness, and intelligence. The knowledge test measures these factors silently by proxy because all of them are needed to achieve a high level of knowledge. If the knowledge measure would be stripped of such associations, how much would be left of its predictive power? Pure knowledge independent of motivation, conscientiousness, and intelligence (which is hard to imagine), would merely consist of the stuff that had been learned devoid of its link to enduring personal dispositions. Knowledge is not an enduring trait such as intelligence, or conscientiousness, it is acquired and, if not used, forgotten over the years. Its causal leverage is confined to the narrow range of the tasks to which it pertains, in this case the natural science content of the medical curriculum.Applicants for medical school in Germany are usually well informed about the tests, which are in store for them. They prepare for the test if they judge their chances as sufficiently high, otherwise they neither submit an application, nor spend time for preparation. If competition is strong, and it certainly is with a selection rate of almost 30% in Hamburg in 2011, then the level of preparation required to stand a chance rises and with it the effect of self selection into or out of the pool of applicants. Thus the mere presence of the test exerts a selective force even before the first multiple choice box is checked. This selective force also promotes a high level of ability in the accepted 30%, and if the ceiling of the test is approached its variance is depleted. High level of ability and depletion of variance both work together to reduce whatever correlation might be found between the test and outcome variables reflecting study success. In the end all applicants are well equipped to live up to the natural science demands of the curriculum and no covariance with differential outcome in this respect is left. The success of the test will have erased the possibility to demonstrate its effectiveness.Empirical bivariate predictor/outcome correlations cannot be taken as measures of predictive validity if indirect selection and range restriction exist. Correction methods are available and should be used. For practical purposes Thorndike’s case C formula is a relatively straightforward solution to the range restriction problem, provided distributional assumptions are met. With EM and MICE more precision is obtained when distributional requirements are not met, but access to a sophisticated statistical package such as R is needed.Can the results of our study regarding a compensatory selection decision be transferred to student selection scenarios that use multiple steps with a single criterion each? Imagine that applicants are shortlisted for a cognitive test based on their hGPA, but the following selection decision is based only on their test score. The range restriction on the hGPA is difficult to estimate as we have to deal with a self-selection bias: applicants might not decide to apply if they think that they do not stand a chance. If solely a cognitive test would be used for the final selection decision (without the possibility to compensate a low test score by other means), a stronger range restriction on the test scores would occur. Then correction for compensatory selection would be unnecessary, but correction for range restriction would have a larger effect. Therefore we think that this correction is even more important to determine the predictive validity when an admission test is used as a single criterion.


Inline and crossline profiles were acquired at equivalent depths of 5 cm, 10 cm, and 20 cm. Depth‐dose curves were acquired using EBT2 film and an ion chamber for both field sizes. Finally, a RANDO phantom was used to simulate an actual TBI treatment. At this extended SSD, care must be taken using the planning system as there is good relative agreement between measured and calculated profiles for both algorithms, but there are deviations in terms of the absolute dose. Acuros has better agreement than AAA in the penumbra region.Accurate dose calculation and treatment delivery is essential for total body irradiation (TBI). In an effort to verify the accuracy of TBI dose calculation at our institution, we evaluated both the Varian Eclipse AAA and Acuros algorithms to predict dose distributions at an extended source‐to‐surface distance (SSD) of 400 cm. Measurements were compared to calculated values for a 6 MV beam in physical and virtual phantoms at 400 cm SSD using open beams for both PACS number(s): 87.55.kd Due to the aforementioned toxicity, it is imperative to ensure accurate dose deliveryThe TBI dose calculation at an extended SSD is typically based on a point‐dose calculation approach.The goal of this study is to assess the dose calculation accuracy of the Eclipse analytic anisotropic algorithm (AAA) and Acuros algorithms  at an extended SSD of 400 cm in both heterogeneous and homogeneous media. Other studies have explored this subject utilizing the AAA and ADAC Pinnacle  albeit at much shorter SSDs of less than 180 cm.All dose calculations were completed in Eclipse v. 11.0.47 using the analytic aniostropic algorithm (AAA) and the Acuros algorithm, both commissioned for clinical use. An energy of 6 MV was used, the calculation grid size was 2.5 mm, and all heterogeneity corrections were turned on. In Acuros, dose to medium was used. Plans were normalized to match the number of monitor units (MU) delivered at the linac during the various measurements. The source‐to‐surface distance (SSD) or the source‐to‐axis distance (SAD) in Eclipse was matched to the setup at the linac during the measurements.40×40 cm2 projected a field size of 160×160 cm2 at this distance. This not only made it difficult to acquire data due to the large field size, but it was difficult to find a phantom that was large enough to provide adequate scatter equilibrium. Therefore, in this work, we used a 5×5 cm2 field size for most of the measurements, which projected a field size of 20×20 cm2 at 400 cm SAD. This was much more manageable for acquiring relevant information and allowed for scatter equilibrium in the phantom. We did acquire data with the clinical field size for comparison although the goal here was not to commission a clinical system, which would require additional measurements.The goal of this work was to assess the accuracy of the dose calculation algorithms at an extended SAD of 400 cm. This geometry posed problems as our clinical field size of 5×5 cm2 to project a field of 20×20 cm2 at 400 cm SAD.Measured profiles were obtained with an IBA Blue Phantom2  water tank using two CC13 ion chambers (IBA Dosimetry); one field detector and one reference detector to reduce the effect of instantaneous machine output fluctuation. The water tank was set up with a 400 cm SSD to mimic the location of the patient in our TBI delivery. The field size was set to This geometry posed a practical problem as the beam entered through the side of the tank rather than the through the water surface. As the beam entered the tank through the plastic wall,3). Inline and crossline profiles were obtained at equivalent depths of 5, 10, and 20 cm. The scanning speed was reduced to 0.3 cm / s to reduce noise. In Eclipse, the same beam geometry was created using a 40×40×40 cm3 virtual water phantom and the dose was calculated using both algorithms. Profiles at the three respective depths were extracted. The calculated and measured profiles were plotted together to analyze any deviations at the extended SSD.we corrected the depth of the profiles to account for the change in density . We obtained a profile using the ImageJ software package (http://www.imagej.nih.gov) and the values from the red channel, only.Due to geometric and physical limitations of the scanning water tank imposed by the wall, we measured the PDDs in two ways; first using Gafchromic EBT2 film  and second using a PTW parallel plate ion chamber  in a For the ion chamber measurements, the chamber was placed in a milled piece of solid water and we acquired readings at depths of 0, 0.5, 1, 1.5, 2, 3, 5, 7, 10, 15, 20, and 26 cm, keeping the phantom SSD at 400 cm. We extracted the PDD from Eclipse by obtaining a profile across a Solid Water phantom for both AAA and Acuros. We normalized all PDDs so that the maximum dose was 100%.To assess the accuracy of AAA and Acuros at calculating doses at extended SSDs including heterogeneous media, we utilized several different phantoms. First, two homogeneous Solid Water phantoms, 19 and 31 cm thick, were used to simulate different patient separations with the central slab holding a Farmer‐type Exradin A12 ion chamber . Second, a heterogeneous phantom was made from a 17 cm thick Styrofoam block sandwiched between two solid water slabs of 2 cm (anterior) and 3 cm (posterior) with a slot cut for the A12 ion chamber in the Styrofoam phantom.5×5 cm2 and 40×40 cm2 field sizes, 1000 MU each.We scanned the phantoms on our Siemens Somatom Sensation CT simulator  using the clinical pelvis protocol  and sent to Eclipse. The phantoms were scanned twice, once with the ion chamber in place and once without the chamber to assess the effects of the presence of the chamber. We setup the phantoms with the chamber at 400 cm SAD and irradiated them with We mimicked this beam delivery geometry in Eclipse and the dose to the ion chamber was calculated by contouring the active volume and finding the mean dose to this volume calculated with AAA and Acuros. We recorded the dose calculated on both the scans with and without the chamber present to assess the accuracy of each algorithm accounting for the perturbation of the ion chamber. These doses were compared to the measured dose delivered at the linac.40×40 cm2 field size to mimic our clinical TBI delivery. EBT2 films were placed between two different slices in the RANDO phantom; the level of the superior lung (slice 12) and the level of the lower lung (slice 18). We delivered 1741 MUs per field equating to about 215 cGy at the midplane of the phantom at the umbilicus level from AP and PA beams.We setup the RANDO phantom  with a 400 cm SAD to the umbilicus midplane and a To convert the film optical density to dose, we irradiated six films to doses of 0, 50, 175, 200, 225, and 250 cGy using the Solid Water phantom at a SAD of 400 cm to account for any energy dependence in the film. All films were scanned using the Epson v700 and the red color channel, only. The films were converted to dose in the Dose Lab Pro software .We scanned the RANDO phantom on the Siemens CT scanner and the AP/PA beam geometry was mimicked in Eclipse. The dose planes from slice 12 and 18 were extracted from Eclipse to be compared to the film measurements. Using the Dose Lab Pro software, relative gamma analysis was performed on the two different planes for both AAA and Acuros. The gamma analysis was completed using both a 3% dose difference/3 mm distance to agreement and 5% dose difference/3 mm distance to agreement.<2% and 2 mm), except in the out‐of‐field region and in the transition regions of the penumbra. The out‐of‐field region might not affect the dose distribution depending on the TBI delivery method. For example, in our clinic patients are treated with 40×40 cm2 fields at an extended SSD so the effect of the out‐of‐field region is minimized.The areas of interest in the profiles are the transition regions where there are discrepancies larger than 2% or 2 mm between the calculated and measured profiles. Acuros demonstrated more sensitivity to perturbations in material density than AAA. When the chamber was included in the CT image in Acuros, the calculated dose changed by up to 1.3% in the Solid Water phantom. In the heterogeneous phantom, the change in the dose calculated with and without the chamber present was up to 25%. In comparison, in AAA it was only up to 16%. This extra sensitivity in Acuros is due in part to the ability to account for physical processes in dose deposition rather than simply modeling them like AAA.The majority of the failing points are found around the periphery of the phantom. This is attributed to the fact that the edge of the film extended beyond the phantom and, therefore, some dose was delivered to the film, whereas in Eclipse, no dose is deposited outside of the phantom. The points inside the phantom showed much better agreement. The profiles in In this study, we evaluated AAA and Acuros at an extended SSD of 400 cm during TBI, which has not been previously investigated. TBI has an important role in conditioning patients for bone marrow transplant in that it both eradicates malignant cells and prevents rejection of donor hematopoietic cells via immunosuppression; however, it does have side effects that may lead to chronic morbidity. To assuage the risk of toxicity, treatment accuracy is of utmost significance, and the use of the treatment planning system can provide three‐dimensional dose distributions to assist with the clinical decision‐making.3 planning system at 100 cm SSD for TBI using a moving couch, and compared measured data to the 3D pencil beam and the superposition convolution algorithm. Hussain et al.Several studies have looked at the accuracy of various treatment planning systems and techniques, although none of them considered distances greater than 200 cm. Lavallee et al.The major finding of this study is that the Eclipse planning system tends to underestimate the dose delivered at extended SSDs. This can be seen in the PDDs and the heterogeneous point dose measurements. The relative dose distribution compares well with the measurements, as seen in the profiles and gamma analysis with the RANDO phantom. The results in this study show that AAA and Acuros are comparable in calculating relative isodose distributions at extended SSDs, with a slight edge given to Acuros in the penumbra region.With this result in mind, the planning system should not be used to determine the MUs needed for a clinical TBI delivery and additional commissioning measurements are required to clinically implement a TBI program. The relative dose distributions can be used to aid in planning decisions, such as lung blocking.One area not covered in this paper was the use of compensators, blocks, or scatter screens. We did not analyze these devices as the inclusion of high‐Z materials adds uncertainty to the calculated dose and modeling devices that are outside of the patient can be difficult. As the focus here is purely the accuracy of AAA and Acuros at an extended SSD, we felt these were beyond the scope of the paper and will be considered in ongoing research.The validation of the dose calculation algorithms at extended SSDs of 400 cm opens the doors to more exotic TBI deliveries in the future, although additional commissioning is required to validate that the out‐of‐field differences do not compromise the delivered dose. For example, the MLC could be used to block the lungs to eliminate the need to cut blocks. This also opens the possibility of using a field‐in‐field technique to deliver a more homogenous dose. The greatest advantage of using the planning system is the ability to visualize a three‐dimensional dose distribution in the patient.The AAA and Acuros dose calculation algorithms were assessed for accuracy in calculating isodose distributions for TBI at an extended SSD. The acquired data were measured using various homogenous and heterogeneous phantoms. Results have shown that the relative dose distribution achieved with both AAA and Acuros agree well with measurements but, in absolute dose, there are deviations that can exceed 10%. Therefore, it is not recommended to use the Eclipse planning system to calculate MUs for TBI treatments at extended SSDs. The relative dose distributions can be used to assist with treatment planning decisions such as lung blocking. Acuros shows slightly better agreement in the penumbra region than AAA. These discoveries may subsequently lead to the creation of more novel dose calculation and treatment delivery techniques in the future.Creative Commons Attribution 4.0 International License.This work is licensed under a


Due to their wide band gaps, III-N materials can exhibit behaviors ranging from the semiconductor class to the dielectric class. Through an analogy between a Metal/AlGaN/AlN/GaN diode and a MOS contact, we make use of this dual nature and show a direct path to capture the energy band diagram of the nitride system. We then apply transparency calculations to describe the forward conduction regime of a III-N heterojunction diode and demonstrate it realizes a tunnel diode, in contrast to its regular Schottky Barrier Diode designation. Thermionic emission is ruled out and instead, a coherent electron tunneling scenario allows to account for transport at room temperature and higher. III-N materials are today at the heart of continuous academic and industrial efforts worldwide. With applications in lighting, radio-frequency or power technologies, Gallium, Indium and Aluminum Nitride alloys offer versatile and outstanding platforms that enable high performance electronics and enhanced solutions in multiple sectors.4, thereby paving the way to new and greener energy converters with a market expected to ramp up in the forthcoming years.Due to its intrinsic properties, GaN is nowadays drawing a lot of attention in the power electronics area as it leads to lower conversion losses at higher frequency compared to Silicon or Silicon Carbide devices. Multiple leading companies have already demonstrated GaN power technologies with extremely promising results5, it gives rise to a high electron concentration combined with a high electron mobility.At the core of most of these GaN power devices lies the AlGaN/GaN heterojunction due to its exceptional properties, in particular the existence of a two-dimensional electron gas. Finding its origin in spontaneous and piezoelectric polarization8, dielectrics on the other hand11, which can depend on their doping and on their electromagnetic environment. With the use of this analogy, we are able to map the energy band diagram at the rectifying contact vicinity in a direct way in order to address the underlying transport mechanisms. By combining the Transfer Matrix formalism12 to compute the system’s transparency and the Tsu-Esaki current formula14, we describe the forward conduction regime of the heterojunction diode with respect to applied voltage and operating temperature.In this work, we propose to draw parallels between an AlGaN/AlN/GaN heterojunction diode and a Metal/Oxide/Semiconductor (MOS) contact by using the duality found in III-N wide band gap materials: semiconductors on the one handWe show thereby that the III-N heterojunction diode realizes a tunnel diode and rule out thermionic emission, too often incorrectly used to capture such architectures. Through this approach we propose an alternative path of understanding the physics of III-N heterostructures and devices.17 where the AlGaN layer is often referred to as the barrier layer, the AlN as the spacer layer and the GaN as the channel layer which contains a Two-Dimensional Electron Gas (2DEG) at the AlN/GaN interface. The system is completed with a surface metal on top of the AlGaN, more specifically Titanium Nitride (TiN). A common approach to studying this system is the use of a Poisson-Schrödinger simulator which allows the derivation of the energy band diagram of the contact and captures the existence of the 2DEG18. We propose here an alternative approach to the problem.We start by considering an AlGaN/AlN/GaN double heterojunction, a widely used designb) where the rectifying contact part or anode  can be mapped on an effective MOS contact (a).To allow an equivalence between the TiN/AlGaN/AlN/GaN contact and a MOS contact we make two main assumptions. First we assume that the AlGaN and AlN layers are depleted from free carriers, thus allowing to consider purely their dielectric nature and equate them to the gate oxide found within a MOS. Then we assume the GaN channel layer to be a n type semiconductor which will be the stage of an electron accumulation layer as found at the semiconductor/oxide interface of a MOS contact. Figure V is the metal potential (referenced to the bulk GaN supposed grounded), Vfb the flat band potential, Vox the potential drop across the oxide and Ψs the surface potential of the semiconductor which translates the amount of band bending in the accumulation layer.This analogy allows us to employ the main equation used to describe MOS capacitors with a first focus being the derivation of the energy band diagram. We start by considering only the rectifying contact part and express the potential equilibrium as found in a MOS capacitor:W is the metal’s work function, χ the electron affinity of GaN and (EC − EF) the energy difference between the bottom of the conduction band and the Fermi energy in the bulk GaN.We detail now the different terms of this equation when applied to the Metal/AlGaN/AlN/GaN contact. The flat band potential expresses the difference between the Fermi levels in the metal (TiN) and in the semiconductor (bulk GaN).Vox is concerned, we recall that III-N materials have polar bonds. Within the bulk, the dipoles created by each chemical bond are canceled by the neighboring ones, two by two. However, at a hetero-interface this balance is no longer present and polarization surface charges develop at them. Figure As far as σs denotes the accumulation charge (mobile electrons) per unit area in the GaN accumulation layer and CAlN and CAlGaN denote the equivalent AlN and AlGaN capacitances per unit area respectively. 5 and the piezoelectric part is determined following19 by assuming the AlN and the AlGaN to be fully strained on a relaxed GaN layer.By taking into account spontaneous and piezoelectric charges and expressing the continuity of the normal component of the electric field in the structure, the voltage drop across the AlN and AlGaN layers reads:σs can be related to the surface potential Ψs by solving Poisson’s equation20:σs is taken to be negative when Ψs is positive and vice versa. n0, p0 correspond to the electron and hole concentrations in the bulk GaN, NC and NV to the GaN conduction and valence band effective density of states and LD to the Debye length written as:F− and F+ functions are defined as:F3/2 corresponding to the normalized Fermi-Dirac integral Fj(x) with order j = 3/221:s at the GaN/AlN interface, which in turn determines σs and finally Vox.The surface charge density mentclass2pt{minimTo illustrate the procedure, we apply it to the computation of the band diagram of a reference structure and more precisely we focus on the conduction band profile. The main operating and structural parameters used are summarized in Table 5. Note that the profile of the conduction band from the bulk GaN (at z = −50 A) to the GaN/AlN interface (z = 0 A) is shown for the sake of clarity and was not calculated explicitly. Indeed only the amount of band bending at the surface of the GaN referenced to the bulk, where the position of the Fermi energy is known through n0, was calculated.Figure ns = 1e13 cm−2 which agrees well with experimental values reported for similar heterojunctions16.We observe that the existence of the 2D electron gas, or the electron accumulation layer, naturally arises from the calculation and is induced by the strong polarization charges found within the hetero-structure. The extracted sheet carrier density within the accumulation layer is 0.25Ga0.75N barrier with 6 nm left above the AlN spacer. For the purpose of this study, interdigitated diodes , expresses the length over which a contact, ohmic in the TLM case, is effectively operating. The concept can be extended to nonlinear contacts and corresponding nonlinear transmission linesLeff over which the current is assumed constant. Through this simplification a 1D approach is possible with a reduced contact surface S = 2Leffω, where ω stands for the anode width.To account for this feature and avoid 2D calculations to reproduce the on state current, we propose a compromise between the regular 1D surface independent current emission Fig.  and the 0.25Ga0.75N barrier with a targeted thickness of 6 nm left above the AlN spacer. This strategy is common in such architectures and offers the benefit of reducing the turn-on voltage of the diode25 allowing more current to be delivered in the on state, a critical feature for end users.As detailed in the previous section, the rectifying contact of the diode under study is realized through a partial recess of the Alns = 7.3e12 cm−2. C(V) measurements performed on representative test structures reveal an experimentally smaller value falling in the range 1e12 cm−2 to 3e12 cm−2.We derive the band diagram of the recessed diode using the same set of parameters as in the reference structure Table  and adju3N4 passivation layer opening using Fluorine species (F−) followed by the Al0.25Ga0.75N etching using Chlorine species (Cl−). Fluorine implantation through a similar process was already reported in the AlGaN barrier by coworkers26 and we believe that within the etching condition used, negatively charged ions contaminate the active layers, more precisely the AlGaN left under the TiN metal.To explain this difference, we turn back to the etching process steps which allow the anode contact recess. The process sequence uses Reactive Ion Etching and comprises the Siσ21 in equation  to region i = N + 1  can be derived as a function of energy:Locally the shape of the electron wave function Φ33. In the coherent tunneling limit and none-interacting electrons, the current density reads:fL and fR represent the equilibrium distribution functions in both reservoirs, indexed L and R, connected to the quantum conductor and T denotes the conductor’s transmission probability.In order to derive the current flow through the contact, we follow the Landauer vision of transport in a mesoscopic system where its quantum resistance is expressed in terms of the transmission and reflection properties of the structure36, carbon nanotubes37, or quantum dots38.The use of such an approach to mesoscopic transport has proved to be versatile and a powerful tool which has been applied to various systems such as molecular junctions and transistors14:T is the transmission probability at transverse energy, that is to say in the transport direction, and which will be evaluated through the Transfer Matrix formalism. The logarithmic term arises from the assumption that the occupancy functions fL(R) follow the Fermi-Dirac distribution in both leads. The metal (TiN) and the electron accumulation layer (2DEG) are treated here as incoherent reservoirs where temperature dictates the precise shape of these distributions. The summation from the bottom of the conduction band (E0) at the GaN/AlN interface to a high energy cut-off allows to account for electron emission from the GaN accumulation layer at different energies. Therefore multiple elastic processes, from direct tunneling in the forbidden band gap of the effective oxide (AlN and AlGaN) to thermionic emission over the potential barrier (above the AlN), are taken into consideration which is represented schematically in Fig. In the case of parallel wave vector conservation and effective masses for each parabolic band of interest, equation  can be rR to be constant at a given temperature within the voltage bias range we are about to explore. The effect of the access resistance is accounted for by setting the effective voltage drop across the rectifying contact in the right hand side of equation  = 2ωLeffJ(V)  Fig. , where ωS denotes the rectifying contact surface, A* denotes the modified Richardson constant, Φb the barrier height and η the ideality factor. Figure a) and 425 K (b). The adjustable parameters extracted from each fit are  at room temperature and  at 425 K using S = 2ωLeff. Although the agreement seems good, such fits miss completely the physics of the device which we are about to show. On the one hand high ideality factors are synonymous of underlying tunnel events39 which thermionic emission does not account for. On the other hand Φb and η need to have strong temperature dependencies in order to capture the evolution of the current, another sign of the irrelevance of such a physical picture in the present case.Before presenting the results of our calculations we recall a widely used empirical formula to reproduce the on state current of several different types of diodes including the studied architecture, the thermionic formula:40. In the present case, R is adjusted to fit the ohmic regime of the diode above the turn-on voltage and is the single free parameter once the calculation is calibrated at a given temperature.Figure 41. Overall, within the operating voltage and temperature range, no thermionic processes participate to the transport in the forward conduction regime. We infer that the use of the thermionic equation for similar devices as it is commonly done, is bound to return incorrect parameters and lead to misinterpretations.Figure 42.The derived electronic transport scenario reveals that the recessed TiN/AlGaN/AlN/GaN realizes a tunnel diode with large output currents. More precisely, the formalism employed suggests that this diode is the stage of coherent electron tunneling events at the vicinity of the anode at room temperature and even higher, a property that would be worth investigating more deeply. From a wider perspective than conventional power conversion, we believe that ultra fast operation could be possible using more compact and fine tuned designs in order to achieve rectification at very high frequencies such as in the infrared spectrum43. A comparable argument could be made as far as the Al content in the AlGaN barrier and in both cases a compromise could be possible. Moreover, the reduction of the AlGaN thickness under the TiN metal would also lead to higher transparency. Through further recessing, the impact on the 2DEG arises. For the extreme case of full recess, the 2DEG is removed below the anode metal and a different type of contact is realized: a lateral Metal/GaN contact24 for which the transport mechanisms would be worth investigating thoroughly. Finally, for thicker barriers  the coherent tunneling picture might break down due to the loss of phase coherence. Indeed, one cannot rule out incoherent scattering processes over longer tunneling distances and more a general tunneling approach might be required to describe a wider variety of heterostructure designs.Beyond the studied diode design, the sensitivity of electron tunneling to potential barrier heights and thickness raises different questions. First, the removal of the AlN layer would allow higher transparency as far as electrons propagating from the 2DEG to the metal, though it would also imply lower carrier concentration and higher access resistance. Indeed the AlN layer is known to lead to improved sheet resistance in the electron channel due to stronger polarization and enhanced confinementVia an analogy with a MOS contact and current calculations based on the Tsu-Esaki formula, a coherent tunneling transport picture could be provided as far as forward conduction is concerned in a III-N heterojunction diode. This result contrasts the common approach involving thermionic emission which can lead to invalid and misleading physical interpretations. We believe that, in essence, the proposed approach which highlights the importance of field effect and takes into account natively electron emission at multiple energies, can be applied to other architectures and materials. As far as III-N heterojunction applications are concerned, we may cite RF or power GaN High Electron Mobility Transistors for which the gate electrostatic control and leakage could be tested on a solid basis. We may also mention III-N LED which involve multiple quantum wells and where transport in the forward regime could be explored more thoroughly.48. The good agreement between experimental and calculated data proves that such events do not play an essential role within the device and associated conduction regime explored. Nonetheless pushing the reasoning further to incorporate such effects would provide a larger frame of investigation. Other refinements could be further implemented such as describing the access resistance in better details to capture its temperature variation for example. One may also consider self-heating effects which mainly occur for high current densities and that would open broader voltage ranges to be analyzed. Finally, the energy quantization of the 2DEG, which was treated as a classical incoherent electron reservoir, would be worth evaluating.We emphasize that within the coherent tunneling framework used, questions related to trap assisted events or inelastic tunneling may ariseIII-N on Silicon growth was realized via MOCVD using a single chamber closed coupled showerhead equipment manufactured by AIXTRON capable of fully automated handling of 200 mm wafers. Au free process integration was carried out using CEA-LETI’s CMOS facilities on the basis of a process flow comprised of approximately 80 technological steps. Electrical characterization was performed by the use of a Tesla 300 mm semi-automatic prober and an Agilent B1505A power device analyzer. All numerical calculations were performed on specifically developed scripts and were double checked using various commercial and open source coding environments.The datasets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.Supplementary information


A complaint from a patient can have a serious impact on the well-being of dentists. Little is known, however, about the nature and the extent of this impact.Therefore in 2013 an anonymous survey was conducted among 955 dentists and dental specialists who were involved in a complaints procedure dealt with by the Complaints Committee of the Royal Dutch Dental Association (KNMT) in the period of mid-2008 to mid-2013.In total 413 (43 %) of these dentists participated in the study. As a result of a formal complaint 71 % of the respondents experienced a considerable impact in their professional practising, while 52 % stated that it had  seriously influenced their attitude towards colleagues and patients. Furthermore, 60 %  mentioned effects of a complaints procedure regarding their mental and/or physical well-being.Being confronted with a formal complaint from a patient leads to a considerable impact on dentists’ professional practice and personal well-being. It is remarkable this did not only pertain to a ‘negative’ impact, but also to a ‘positive’ impact. Despite unpleasant feelings, several dentists regarded the complaint as a ‘wake-up call’. Furthermore, given the relatively high number of successful mediation attempts it can be concluded that this form of complaint handling appears to be a successful way of solving problems that have arisen between patients and dentists. This article is an edited translation of a previously published original article written in Dutch . In 2012Health Sector Client Complaints Act and is meant for members of the KNMT, the largest professional organisation of dentists in the Netherlands with about 7,200 registered individual dentists and dental specialists [The complaints procedure of the KNMT meets the requirements such as laid down by the Dutch cialists , 7. Thiscialists . In addicialists .An overview of the total number of complaints against Dutch dentists filed annually is not available. Besides the KNMT and ANT complaints procedures there is also the possibility to lodge a complaint with the regional health care disciplinary boards. Furthermore, an as yet unknown number of complaints are lodged against dentists in the civil courts and with the Public Health Care Inspectorate. In addition, when determining the number of complaints against dentists, the fact that more and more institutions have their own boards of complaint should be taken into consideration. However, in 2013 the KNMT complaints procedure dealt with 957 letters of complaint, 454 of which were in fact followed up in a procedure as a formal complaint . In thatFrom some personal experiences it becomes clear that dentists are not often aware of the possibility that they could become involved in a complaint procedure and that, if this does happen, it may have a serious impact. Sleepless nights, thoughts going round in circles and health problems are mentioned, as well as the time a procedure takes and the stressful build-up to the hearing. Feelings of insecurity taking away the pleasure of work and the tendency to see every patient as a potential threat is also reported . In thisWhile there is some data available on the nature and seriousness of the impact of a complaint on care providers, little is actually known when it concerns dentists. More knowledge is however desirable: it may contribute to raising awareness within the profession that one may be faced with a formal complaint and should be prepared how to best cope with this, both personally and professionally. In addition, more knowledge can be used to inform dentists - and dental students - about how complaints can best be prevented. Eventually this will contribute to a higher quality of patient care. Given the sparse knowledge on this topic, the aim of the present study was investigate the impact of a formal complaint (and the following procedure) on dentists’ professional practising and personal well-being.The study was built up in two phases. It started in the spring of 2012 with a pilot study, in which semi-structured oral interviews were held with 17 dentists and dental specialists who had been in a KNMT complaints procedure , 20. TheThe research group was defined by all Dutch dentists and dental specialists against whom a formal complaint had been lodged and dealt with via the KNMT complaints procedure in the period of 2008 up to and including the spring of 2013. For this occasion, exclusive permission from the KNMT Executive Board was granted to address this group. In this period 1 or more complaints against 1,013 dentists and dental specialists were dealt with via successful mediation by one of the Regional Mediation Boards (RBR) and/or via the Central Complaints Committee (CKC). The complaints procedure of the Royal Dutch Dental Association (KNMT) offers patients two options. The first option is mediation between the patient and the dentist by a Regional Mediation Board (RBR) or the Specialist Mediation Board (SBR). In case the mediation failed or the patient refuses to try mediation, the second option is for the patient to file a formal complaint with the Central Complaints Committee (CKC). The CKC can declare the complaint either entirely or partially legitimate or unfounded.By the end of May 2013 this group was first contacted in writing. They received a letter in which the survey was announced and its background explained. Because the topic might trigger memories people were not overly keen to be questioned about, dentists who would rather not participate were offered the opportunity to report this: 58 prospective participants in the survey did so. The remaining 955 dentists and dental specialists received the questionnaire a few weeks later. Ultimately, after two reminders 413 (43 %) of them responded.As for gender, age group and place of qualification the divisions within the group of respondents did not show significant differences from those in the intended research group. Comparison between respondents and non-respondents with regard to the way in which the complaint had been dealt with and, if applicable, the verdict from the Central Complaints Committee (CKC), also showed no significant differences.It may safely be assumed that, as far as the aforementioned characteristics of the dentists and dental specialists in the survey are concerned, these constitute a reasonably representative reflection of the entire group of dentists and dental specialists against whom in the research period a complaint was dealt with via the KNMT complaints procedure. The data collected was analysed by means of SPSS .In the opinion of the dentists questioned, in 58 % of all cases the cause of the complaint had to do with dissatisfaction with treatment patient, while 29 % refers to patient behaviour (‘an attempt by the patient to ‘squeeze every last drop out of the situation’), 20 % to patient communication, 19 % to costs of treatment and 12 % to another aspect  of the dentists questioned said that the complaint against them had been dealt with via successful mediation by the Regional or Specialists Mediation Boards (RBR/SBR), whereas 17 % stated that the patient had withdrawn the complaint during the procedure. In all other cases (32 %) the complaint had been dealt with by the CKC, directly or after a failed attempt at mediation.The complaints against 130 dentists who appeared before the CKC were declared entirely legitimate in 23 % of the cases, and partially legitimate in 18 %. 55 % of the cases were declared unfounded; in 3 % of the cases parties still agreed on a settlement and in 1 % the complaint was declared unsustainable. Looking at the total number of complaints that were mediated, withdrawn and dealt with this comes down to 13 % of  legitimate complaints.Table p < 0.05).Being confronted with a complaint had affected 29 % to a large extent or strongly in their personal professional practising, whereas 42 % reported they were affected somewhat. 29 % stated not to be affected Table . DentistTable p < 0.05).As is shown in Table From Table Furthermore, 60 % stated that the after effects of the complaint affected their mental and physical well-being Table . Dentistp < 0.05).All things considered it appears that 21 % of the dentists did not report any impact, 6 % only a positive impact, 42 % a mixed impact and 31 % only a negative impact Table . MoreoveOn the whole, 32 % of the respondents indicated that they were not burdened by unpleasant feelings as a result of the complaint. Others were troubled at the most for some weeks (26 %), some months up to a year (31 %), or longer than a year (11 %). It was noted that only one person was off sick as a result of the complaint, but just for a few days.In most of the cases (75 %) the relationship between the dentist and the patient was permanently damaged as a result of the complaint and the complainant had left to go to another dentist; in practically all cases to another practice Table . In 8 % Nearly two thirds (64 %) of the dentists said that as a result of the complaint they had become more alert on certain aspects of care or had made changes. Table In the present study the focus was on the consequences of a complaints procedure for dentists and dental specialists. The questions were not limited to information about the effects on the professional practising of these health care providers and their attitude towards patients, colleagues and/or staff, but also pertained to their mental and/or physical well-being. Eight out of 10 respondents indicated that they had experienced a considerable impact in at least one of these areas. It is remarkable this did not only pertain to a ‘negative’ impact, but also to a ‘positive’ impact. It is true that two thirds of the respondents mentioned unpleasant feelings as a result of the complaint, but at the same time 4 out of 10 dentists  regarded the complaint as a ‘wake-up call’. So, the complaints procedure obviously also generates a ‘spontaneous’ effect on the profession with regard to the quality of care .Several studies indicate that in relatively many cases complainants are not satisfied with the outcome of a formal complaint procedure . This haThus from the many successful mediation results it can be derived that in dentist - patient communication there is room for improvement. About half of the respondents indicated they had learned to better improve at this point. This was also suggested by Boers and Sanaan and, for that matter, the respondents themselves also agreed . SeveralNobody looks forward to receiving a complaint and therefore it is not strange that unpleasant feelings arise when this happens. Many a dentist does not seem to be upset for too long and sees a complaint as a warning. But it also becomes clear that other dentists will still be seriously ‘out of sorts’ when they are confronted with a complaint. They feel their good reputation is blemished, experience the complaint as a personal let down, lose their self confidence in contacts with patients, colleagues and staff and/or become mentally unbalanced . It is difficult to describe this in general, since personal characteristics naturally play a part. But that the impact is substantial in a number of cases has perhaps something to do with the fact that in oral health care it often concerns long treatment relationships in which trust has developed. This is in the interest of the patient, but also of the dentist. Silverman et al. point out that ’the development of a long term relationship with patients is experienced by most care providers as the most satisfying aspect of their work’ . A complWhen it concerns patient complaints of course it always goes that prevention is better than the cure. Here, first and foremost, the responsibility lies with the dentist himself. The aspects of care in this survey that dentists have changed as a result of a complaint lodged against them can form a leitmotif for prevention. In short: consideration for and attentiveness towards patients, clear and thoughtful explanation of oral health and the pros and cons of treatment, ‘informed consent’ and adequate documentation can prevent complaints. The Institute of Medicine does not describe in vain good communications with patients as 1 in 6 criteria of good medical care . In thisHere contributions can also be made at a more collective level. Of course this already starts in education. Van der Ven et al. advocate that dentists have to be imparted with sufficient knowledge on health care legislation and patient rights in their academic studies and later on via post academic education . In addiIn the perception of several dentists a complaint has to do with a patient who aims to squeeze every last drop out of a situation. From the data of this study it can’t be determined whether this perception is correct. Probably this interpretation stems from the fact that in the Netherlands dental treatment is not or only partially reimbursed for adults. In case of a complaint regarding treatment it is conceivable that dentists experience that patients exploit the situation. Especially, because dentists tend to fail to fully explain the content and costs of a treatment.This study has some weaknesses, which have to do with the type of data. First of all it concerns retrospective data, representing the recollection of dentists regarding thought, feelings and experiences they had in the past. For some the past could be a few years ago and for others some months ago. Respondents can under- or overestimate their earlier reactions. In any case, this forms a risk with regard to the reliability of the data.Furthermore, because of the anonymous character of the data collection it is difficult to determine exactly to what extent these results are representative for all the dentists who were confronted with a complaint in the past few years. Besides, it must be kept in mind that patients can also lodge their complaints elsewhere, including e.g. with the regional health care disciplinary boards. In 2013 a total of 104 complaints against dentists were lodged with these disciplinary boards, 27 (26 %) of which were ultimately declared legitimate . It is kNevertheless, this study yields relevant and new information on the impact of complaints of patients on dentists. This information can be cons id ered acceptably representative since it covers the situation in the Netherlands nationwide over a period of several years. Moreover, from a comparison of a number of relevant characteristics it has been made plausible that the participants in this survey constitute a reasonable reflection of the total population of dentists and dental specialists who were confronted with a complaint through the KNMT complaints procedure.Being confronted with a formal complaint from a patient has a serious impact on many dentists. This not only affects the different aspects of professional practise, but also mental and physical well-being. The handling of a complaint through mediation appears to be preferable to dealing with the complaint by means of a verdict from the CKC. Anyway, dentists for whom the complaint was successfully mediated reported fewer ‘negative’ consequences in certain respects. Moreover, it is not just a matter of ‘negative’ impact , a complaint is often also read as a signal to do things better. To a majority of dentists who are confronted with a complaint this is therefore the reason to change certain matters in the care they render. In doing so, a great deal of attention is paid to improve on communication with patients and on documentation of the care rendered. It is recommended to make this lesson learned also part of dental (post)graduate curricula.


Human lactancy is a simple and cost-effective strategy that influences infant and maternal mortality rates. Skin-to-skin contact (SSC) is an immediate postpartum period strategy that has proven to benefit the initiation and continuation of human lactation and to decrease hospitalization during the first week of life. This study aims to determine the effect of SSC initiation at birth (immediate versus early) in healthy, full-term newborns treated at the Universidad de La Sabana Clinic on the duration of exclusive human lactation.t test will be used for independent samples, and the Wilcoxon rank sum test will be used if the assumptions of normality for the t tests are not fulfilled. The assumption of normality will be evaluated using the Shapiro-Wilk and Kolmogorov-Smirnov tests. Categorical variables in contingency tables will be constructed to assess the independence between variables using the chi-square test, or Fisher’s exact test when the assumption of the number of cases is not met by the values in the contingency tables multiplied by two. This will be calculated as a measurement of the effect of relative risk (RR) with confidence intervals; the adjusted measurements will be calculated using a multivariate regression Poisson model. Variables with significant results will be used in the bivariate analysis, and those with biological plausibility will be used for the adjustment. The analysis will be carried out for a two-tailed type I error level of 5 %. The Stata 11 program will be used for data analysis. An interim analysis will be performed upon the submission of half the expected events (106), setting limits for the early termination of the trial according to the method proposed by Pampallona and Tsiatis (1994). Intervention: There will be two SSC randomization groups: early versus immediate. After completing the neonatal adaptation process and based on the group assignment, the mother will be left with her newborn child in hospital accommodation. Prior to discharge, the Infant Breast-Feeding Assessment Tool (IBFAT) will be applied. Monitoring will initially be performed with a face-to-face assessment between 3 and 10 days of life, followed by monthly telephone calls for 6 months to verify lactation status.A randomized, blind clinical trial will be performed with full-term healthy newborns born at the Universidad de La Sabana Clinic. The blind trial participants will be those persons measuring the results and analyzing the data. The sample size will be calculated for a type I error of 5 %, a two-tailed type II error of 20 %, and an estimated percentage loss of 30 %; 150 infants will be included in each group. Randomization will be performed using permuted, size-6 blocks. Descriptive analysis will be conducted using central tendency and dispersion measurements. A bivariate analysis will be performed to determine which variables are associated with exclusive lactancy at 6 months. For continuous variables, Student’s SSC at birth has shown benefits in the short and long term for both the mother and the full-term newborn. Although the meta-analysis that have been done have shown the benefits of this technique, multiple differences in the SSC interventions have been identified because criteria such as the initiation or duration of SSC (dose) have not been unified. Colombia has a malnutrition risk of 11,4 % in the total population for the period 2012-2014, so it is necessary to promote strategies that generate a positive impact on the duration of human lactation, providing support from the clinical setting of humanized delivery which is included in the IAMI strategy (Instituciones Amigas de la Mujer y la Infancia – Friends of Women and Children Institution). Therefore, we propose that the initiation time of SSC in full-term new-borns is related to the duration of exclusive human lactation.02687685. Registered on 2 February 2016. This study is not yet open for participant recruitment.Registered ClinicalTrials.gov Identifier: NCT The online version of this article (doi:10.1186/s13063-016-1587-7) contains supplementary material, which is available to authorized users. The first 2 h of a baby’s life has been defined as the optimum time to begin human lactation. Skin-to-skin contact (SSC) between newborn and mother in this period improves the chance of successful lactancy in the first hour of life and in the long term , 2. The The SSC strategy has been applied at different times at birth and for different time durations, the latter being understood as being a dose of SSC. Depending on the time of initiation of the SSC intervention, it has been divided into subcategories Table  3]. Alt. Alt3]. Through conducting a randomized, blind clinical trial, this study aims to determine the effects of two different SSC initiation times (immediate versus early) on the duration of exclusive human lactation in healthy full-term newborns treated at the Universidad de La Sabana Clinic.Variability is evident in both clinical practice and the obstetric literature for both the optimum start time for implementing SCC and its optimum duration, which has created heterogeneous strategy results in research studies as well as interpretation. No studies have been conducted comparing the different SSC initiation times regarding breastfeeding, while recommendations have been made to study whether the initiation time makes a difference in the benefits of the technique .Interventions at birth and the practice of separating the baby from the mother at birth have negative effects on the initiation of breastfeeding. A cross-sectional study of the factors involved in the initiation of lactancy within the first hour of life was conducted in different hospitals in Rio de Janeiro between 1999 and 2001 , and foun = 102): initiated at birth, delaying the adaptation intervention until after contact, the duration was at least 45 min until the first feed was completed or the mother chose to withdraw the SSC and the control group, were receiving routine care (n = 102) understanding this to mean that once born, the routine adaptation interventions are applied, separating the newborn from the mother and/or parent. The investigators measured the success of the first breastfeed as a primary result and as secondary results they measured exclusive lactancy until 4 months, thermoregulation in the first hour of life and the mother’s degree of satisfaction. The IBFAT (Infant Breast feeding Assessment Tool) scale was used to evaluate the success of the baby’s first breastfeed. They found that the success of the first feed within the first hour of life was higher in the SSC group  and also higher for the duration of exclusive breastfeeding until the first 4 months of life. Likewise, the thermal stability of the baby was better in the SSC group and mothers also reported greater satisfaction in this group.Carfoot et al.  conducteearly SSC in which the baby and mother have contact at birth and SCC was continued for 4 h. The control group was defined as the post-birth routine care group in which the mother is separated from the newborn in order for adaptation care routines to be applied. They evaluated lactancy independent of whether suction took place at birth or not and they considered 2 to 4 h as adequate time for exclusive lactancy and inadequate for those requiring whole or mixed formula feeding. Significant differences were found in favor of the group using early SSC in exclusive breastfeeding at 24 h of life , at discharge from hospital , and at 14 days of age .Villalón et al.  in Chileimmediate, birth, very early, and early), thus highlighting the need for studies investigating the benefits of the technique in this field.The systematic review by the Cochrane Collaboration  found thbirth group (p < 0.001) compared to the very early group (p < 0.05), but all remained within normal ranges. A faster heart rate stability was found in the SSC birth group compared to early (p = 0.001), there were no significant differences in respiratory adaptation. Stress levels as indicated by the cortisol level were lower in babies who were in SSC for more than 60 min compared to those who were in SSC for less than 60 min (p = 0.046). This study concludes that early SSC within the first 5 min of life, with a continuous duration of more than 60 min, reduces the stress on the baby and improves cardiopulmonary stability at birth.As to the time of SSC and its duration, Takahashi et al.  evaluateearly SSC, in which the newborn was left in SSC with the mother from birth for 2 h, postponing interventions up until that point; and routine care, in which the baby was taken to the radiant heat lamp once the umbilical cord had been cut in order to proceed with the interventions. The success of the first breastfeed was evaluated as a secondary result using the IBFAT and the average first lactation. In the SSC group, the self-efficacy in human lactation (BSES) score was 53.42 (standard deviation (SD) 8.57) versus 49.85 (SD 5.5) in the control group (p = 0.0003). The successful initiation of human lactation was 56.6 % in the intervention group versus 35.6 % in the control group (p = 0.02) and finally, the initiation time of the first feed was 21.98 ± 9.1 min in the SSC group versus 66.55 ± 20.76 min in the routine care group (p = 0.001).In Iran, Aghdas et al.  evaluateVarious tools or tests to assess lactancy have been developed. The IBFAT tool was developed and published by Matthews et al. in 1993 to evaluate the behavior of the baby during sucking and swallowing, with a reliability of 91 % . Using sr = 0.5, p = 0.06 and IBFAT r = 0.49, p = 0.06).Schlomer et al.  evaluateRiordan et al.  initiallTo determine the effect of immediate versus early SSC birth on the duration of exclusive human lactancy in healthy, full-term newborns in the Universidad de La Sabana Clinic.To evaluate the competence of the newborn human lactancy in the first 24 h of life by using the IBFAT instrument among newborns in immediate SSC compared with early SSCTo determine the prevalence for hospitalization and admission to the neonatal intensive care unit (NICU) in the first week of life between the two SSC groups (immediate versus early)RR) = 1○ Null hypothesis: there is no difference in the percentage of healthy, full-term newborns receiving exclusive human breastfeeding for three or more months between the immediate versus early birth SCC groups: relative risk ▪ Full-term newborns who are defined, by obstetric method and confirmed by pediatric method , as being between 37 and 42 weeks of gestation with appropriate weight for gestational age .Human lactation capacity in the newborn within the first 24 h of life and prior to discharge using the IBFAT scale  within the first 24 h of life and prior to dischargeNewborn capacity for human lactation:Measurement of the change in weight from birth to the end of the first week of life: this will only be done with a previously calibrated electronic scale, which will take measurements at birth and in the first week of life. The need for admission to the NICU in the first week of life will be assessed during the first follow-up visit in the first the week of life  will undergo training regarding: SSC after birth in healthy newborns, human breastfeeding concepts , the institutional human lactation protocol and management of the mothers with their newborn baby▪ The mothers who meet the entry criteria will be identified in the obstetrics and gynecology outpatient department at their prenatal appointment. An obstetric history will be conducted by the physician in order to identify risk factors or conditions that may contraindicate the study. Those mothers who meet the criteria for inclusion will be interviewed in order to explain the purpose of the study, its application and other events to be expected. Should they accept the offer of participation, they will sign an informed consent , and measures of immediate and mediate neonatal adaptation will be appliedPrior to discharge, the IBFAT instrument will be applied to the mother and her infant by the research monitor and/or operational coordinator.▪ The first assessment will take place in the first week of life. The mother and the baby will be summoned to the Universidad de La Sabana Clinic and a nursing professional will perform it. This consultation aims to record the birth weight, the effectiveness of human lactation and feeding capacity and the need for hospitalization.▪ Monthly follow-up. This follow-up procedure will take place via monthly telephone calls with the mothers for 6 months, checking their adherence to human lactancy and, in the cases where breastfeeding has been suspended, inquiring about the reasons for this.An electronic information collection instrument will be created and a paper record of the data collected for the study will also be kept. Periodically (every month), the research team will verify the information in the database with respect to the physical record. To reduce errors in information collection, double entry of information is performed.The data will be kept in the research office of the Universidad de La Sabana Clinic and only the research group and regulatory personnel (INVIMA) have access to it if, for any reason, it should be required.24 % babies in Colombia, received exclusive breastfeeding up to 5 months old 9). This was the baseline risk assumed for the sample size calculation . This wa, which cThe 300 newborns will  be randomized using size-6 permuted blocks to ensure that there will be an equal number of participants in the control group and the intervention group. Once the mother signs the informed consent and the entry data for the study has been entered, the operation coordinator of the study will open the opaque envelope, the contents of which determines to which group the mother will be assigned and this information will be recorded immediately in the medical record. The coordinator will verify that the intervention to which the patient was assigned at birth is applied.As to the characteristics of the interventions under evaluation, those who measure the results and who will analyze the data will be blind. To ensure that the blind participant who measures the results will be someone other than the health professional applying SSC, that person will not be in the delivery room and will apply the study measurements to all newborns treated at the clinic without knowledge of whether or not they are study participants.The person conducting the analysis will be given the database in which the variable that identifies whether the research subject belongs to the control group or the intervention group is found; this will then be coded and the code that identifies them will not be available to the analyst.t test will be used for independent samples or the Wilcoxon rank sum test when the assumptions of normality for the t test are not fulfilled. The assumption of normality will be evaluated with the Shapiro-Wilk and Kolmogorov-Smirnov tests. Contingency tables will be constructed in the categorical variables, assessing the independence between variables with the chi-square test, or Fisher’s exact test when the assumption of number of cases per cell in the contingency tables, multiplied by two, is not fulfilled. The relative risk (RR) will be calculated as an effects measurement with confidence intervals, adjusted measurements will be calculated using a multivariate Poisson regression model, for adjustment variables with significant results those with biological plausibility will be used in the bivariate analysis. An analysis will be carried out for a two-tailed type I error level of 5 %. The Stata 11 program will be used for the data analysis. An interim analysis will be performed upon submission of half of the expected events (106), setting the limits for early termination of the trial according to the methods proposed by Pampallona and Tsiatis 1994 [Descriptive analyses were performed using measures of central tendency , location (percentiles) and dispersion (standard deviation and ranges) for continuous variables and absolute frequencies and relative for the categories. Bivariate analysis will be performed to determine which variables  are associated with exclusive lactancy at 6 months. In the continuous variables, the Student’s tis 1994 .The protocol study information will be revised by the Data Monitoring Committee used by the clinic and recruited for the study. This committee will assess the study’s progress, safety data, and critical efficacy endpoints. The DMC reviews unblinded information during the conduct of the study. The information will be periodically revised every 2 weeks.All study participants will be analyzed in the group to which they were originally randomized. Loss to follow-up will be analyzed as explained below:▪ Descriptive analyses of the lost subjects, will be conducted to determine if they are different from those who continued in the study and whether the losses generated imbalance between the intervention and control groups▪ The effect measure, assuming the worst and best scenario for subjects who were lost to follow-up, will be estimatedSSC at birth has shown benefits in the short and long term for both the mother and the full-term newborn. Although the meta-analyses that have been done have shown the benefits of this technique, multiple differences in the SSC interventions have been identified because criteria such as the initiation or duration of SSC (dose) have not been unified. Studies have been conducted with different schemes  without clarity about which of the initiation times of SCC from birth provides the greatest benefits during infancy.Colombia has a malnutrition risk of 11,4 % in the total population for the period 2012-2014, so it is necessary to promote strategies that generate a positive impact on the duration of human lactation, providing support from the clinical setting of humanized delivery which is included in the IAMI strategy (Instituciones Amigas de la Mujer y la Infancia – Friends of Women and Children Institution). Therefore, we propose that the initiation time of SSC in full-term newborns is related to the duration of exclusive human lactation.Human lactation is simple and freely available, provides optimal nutrition for the baby, facilitating their proper growth and development and, therefore, establishing itself as an effective strategy to help reduce disease in the infant population.This study aims to determine the effect of SSC initiation times from birth (immediate versus early) in healthy, full-term newborns on the duration of exclusive human lactation at the Universidad de la Sabana Clinic where the newborns were attended. It also evaluates the human feeding capacity of newborns 24 h after birth by applying the IBFAT scale. Thus, the analysis of weight change in the first week of life and the need for hospitalization and admission to the NICU in the first week of life are also included.This study is not yet open for participant recruitment.