Optimizer convergence and local minima errors and their clinical importance

Two of the errors common in the inverse treatment planning optimization have been investigated. The first error is the optimizer convergence error, which appears because of non-perfect convergence to the global or local solution, usually caused by a non-zero stopping criterion. The second error is the local minima error, which occurs when the objective function is not convex and/or the feasible solution space is not convex. The magnitude of the errors, their relative importance in comparison to other errors as well as their clinical significance in terms of tumour control probability (TCP) and normal tissue complication probability (NTCP) were investigated. Two inherently different optimizers, a stochastic simulated annealing and deterministic gradient method were compared on a clinical example. It was found that for typical optimization the optimizer convergence errors are rather small, especially compared to other convergence errors, e.g., convergence errors due to inaccuracy of the current dose calculation algorithms. This indicates that stopping criteria could often be relaxed leading into optimization speed-ups. The local minima errors were also found to be relatively small and typically in the range of the dose calculation convergence errors. Even for the cases where significantly higher objective function scores were obtained the local minima errors were not significantly higher. Clinical evaluation of the optimizer convergence error showed good correlation between the convergence of the clinical TCP or NTCP measures and convergence of the physical dose distribution. On the other hand, the local minima errors resulted in significantly different TCP or NTCP values (up to a factor of 2) indicating clinical importance of the local minima produced by physical optimization.     

Bayesian methods for assessing importance of effects.

In experimental data analysis when it comes to assessing the importance of effects of interest, 2 situations are commonly met. In Situation 1, asserting largeness is sought: "The effect is large in the population." In Situation 2, asserting smallness is sought: "The effect is small in the population." In both situations, as is well known, conventional significance testing is far from satisfactory. The claim of this article is that Bayesian inference is ideally suited to making adequate inferences. Specifically, Bayesian techniques based on "noninformative" priors provide intuitive interpretations and extensions of familiar significance tests. The use of Bayesian inference for assessing importance is discussed elementarily by comparing 2 treatments, then by addressing hypotheses in complex analysis of variance designs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Deformation bands, the LEDS theory, and their importance in texture development: Part II. Theoretical conclusions

The facts regarding “regular” deformation bands (DBs) outlined in Part I of this series of articles are related to the low-energy dislocation structure (LEDS) theory of dislocation-based plasticity. They prompt an expansion of the theory by including the stresses due to strain gradients on account of changing selections of slip systems to the previously known dislocation driving forces. This last and until now neglected driving force is much smaller than the components considered hitherto, principally due to the applied stress and to mutual stress-screening among neighbor dislocations. As a result, it permits a near-proof of the LEDS hypothesis, to wit that among all structures which, in principle, are accessible to the dislocations, that one is realized which has the lowest free energy. Specifically, the temperature rises that would result from annihilating the largest DBs amount to only several millidegrees Centigrade, meaning that they, and by implication the entire dislocation structures, are close to thermodynamical equilibrium. This is in stark contrast to the assumption of the presently widespread self-organizing dislocation structures (SODS) modeling that plastic deformation occurs far from equilibrium and is subject to Prigogine’s thermodynamics of energy-flow-through systems. It also holds out promise for future rapid advances in the construction of constitutive equations, since the LEDS hypothesis is the principal basis of the LEDS theory of plastic deformation and follows directly from the second law of thermodynamics in conjunction with Newton’s third law. By contrast, all other known models of metal plasticity are in conflict with the LEDS hypothesis. In regard to texture modeling, the present analysis shows that Taylor’s criterion of minimum plastic work is incorrect and should be replaced by the criterion of minimum free energy in the stressed state. Last, the LEDS hypothesis is but a special case of the more general low-energy structure (LES) hypothesis, applying to plastic deformation independent of the deformation mechanism. It is thus seen that plastic deformation is one of nature’s means to generate order, as a byproduct of the entropy generation when mechanical work is largely converted into heat.     

Anesthetics and nitric oxide. Interactions and their importance for anesthesia

Due to its important physiological and pathophysiological actions, the pluripotent signaling molecule nitric oxide (NO) is increasingly of interest in clinical medicine. Despite increasing use by anaesthetists in inhalational therapy for intensive care patients with respiratory distress syndrome, the potential interactions of anaesthetic agents and NO have thus far received little attention. The literature available to date on this topic is somewhat controversial, and highlights the need for additional research in this area. This review summarises the pertinent literature in this area for the anaesthetist and describes potential mechanisms by which anaesthetics may interfere with the synthesis and/or effects of NO in the human body.     

Cross-resistance phenotypes of fluconazole-resistant Candida species: results with 655 clinical isolates with different methods

Candida species test results with two broth macrodilution antifungal susceptibility methods were compared using 655 clinical isolates, and the frequency of fluconazole resistance and phenotypes of azole cross resistance are detailed. A method with an 80% inhibition endpoint (as compared to clear tube endpoint) suggested greater fluconazole susceptibility to C. albicans but had a less pronounced effect on C. glabrata, and seemed to have a negligible influence on results with C. parapsilosis and C. tropicalis. The latter were grouped as susceptible and resistant (based on achievable blood levels), respectively, by both methods. Cross resistance was method dependent and more pronounced with itraconazole than ketoconazole. In vivo correlations are needed to validate the groupings proposed by any in vitro method.     

Normal values in clinical electrooculography. II. Analysis of potential and time parameters and their relation to other variables

The following EOG potential and time parameters from 72 normal subjects were analysed: base value B, dark trough D, light peak L, light induced potential rise L-D, interval between beginning of dark adaptation and occurrence of dark through d and interval between dark trough and light peak l. Their relations to sex, age pupillary diameter, degree of iris pigmentation, refractive error, axial length, corneal curvature and diameter, ocular protrusion and interpupillary distance were assessed. Right eye and left eye samples of the EOG parameters were congruent, although individual differences were sometimes appreciable. The levels of B and D were higher in the female half of the sample. A positive correlation existed between age and D level. L-D was negatively correlated to the degree of refractive error and positively correlated to the ocular protrusion. A positive correlation was found between d and the four potential parameters, and there was a positive correlation between age and l. Practical consequences of the statistical analysis relating to the interpretation of such EOG data are discussed.     

Predicting occupational choice by clinical and statistical methods.

Investigated the accuracy with which occupational choices for 225 male theology students could be predicted from scores on the Inventory of Religious Activities and Interests by 2 experienced counselors and by means of 2 statistical procedures--discriminant function and profile shape. Predictions were compared with 3 criteria: the S's actual choice, a derived choice, and an adjusted choice, with the latter 2 choices obtained from a perceived interest profile completed by the Ss. The percentage of correct predictions was found to vary as a function (and interaction) of the predicted and criterion choices. Percentages ranged from 30% for derived choices predicted by counselors to 54.7% for actual choices predicted by the discriminant-function procedure. Analysis showed that the percentage of correct predictions was affected by the varying difficulty of predicting the several occupations considered, by the realism of the S's choice, by the S's change of interest, and possibly by the lag of stated choice behind a change of interest. Ways in which the findings can be of practical assistance to the counselor in increasing predictive accuracy and in planning a counseling strategy are considered. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the equivalence of clinical and statistical methods.

Based on material from a doctoral thesis, an attempt was made to resolve an inconsistency in Meehl's analysis of statistical vs. clinical methods of assessment (see 29: 3991). "Eight interviewers assessed from 14 to 50 Canadian Army applicants using information obtained from biographical and test data, and from interview conversation. Each applicant was described on a 120-item Q-sort check list. These data were quantified and combined into composite statistical scores (biographical and test data) and clinical scores (Q-sort data). The results indicated that: (a) clinical scores were associated more closely with decisions than were statistical scores; (b) statistical and clinical scores correlated at a low level; (c) the decisions of different interviewers were associated with the same Q-sort, biographical, and test data; and (d) statistical and clinical scores were comparable in reliability." "… this study… strengthens the status of the clinical assessment." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

APA internship selection criteria: Relative importance of academic and clinical preparation.

Surveyed American Psychological Association (APA)-approved internships to assess what criteria are important to internship selection committees and to determine how much clinical experience is desired to make an applicant competitive. The survey also assessed the number of courses and amount of hours of supervised experience in both diagnostics and treatment that internships look for in preferred applicants. A brief questionnaire was sent to 120 APA-approved internships, which resulted in a response rate of 75%, or 90 respondents. Results show that internship training centers emphasize clinical training experience and personal qualifications over traditional academic achievements. In addition, internships look for substantially more hours of supervised clinical experience than the amount the minimum APA-accreditation criteria require. (8 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Global self-esteem: Its relation to specific facets of self-concept and their importance.

Theory and common sense posit that the effect of a specific facet of self-concept on esteem will vary with the importance of the facet, but little support for this proposal was found in a study of late adolescents and young adults. Subjects, particularly those with high esteem, were more likely to have high self-concepts in facets they perceived to be more important, but their importance ratings did not contribute to the prediction of esteem. Unweighted averages of 12 distinct dimensions of self-concept correlated about .7 with Esteem, but weighting each facet by the importance assigned to it by the entire group, by diverse subgroups, or by each individual resulted in little or no improvement. Neither self-concept/importance interactions nor self-concept/importance discrepancies were able to explain much variance in Esteem beyond that which could be explained by specific facets of self-concept. Nevertheless, some support for the effect of importance was found for the Spiritual and Physical abilities facets, and these were the two facets for which the perceived importance was most variable. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Survey on the use of clinical and mechanical prediction methods in clinical psychology.

We surveyed 491 American Psychological Association division 12 (clinical psychology) members regarding their professional use of clinical and mechanical data combination (CC and MC) in making clinical predictions; 183 (37%) responded. This is the first report of CC and MC utilization frequency known to us. Nearly all respondents used CC in practice (98%), while fewer used MC (31%). Respondents gave reasons why they did not use MC, the most common being that it is conceptually misguided. In addition to computing odds ratios for variable comparisons, we constructed a multivariate regression model to predict use of MC, using a bootstrapping method that returns an estimate of the model’s cross-validated validity. This procedure returned the null model: no predictor was powerful enough to replicate upon cross-validation. The extent to which MC was discussed in graduate school significantly mediated nearly all other relationships between variables of interest. Implications of these findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Utility of Albicans ID plate for rapid identification of Candida albicans in clinical samples. Rapid identification of Candida albicans

A clinical study was carried out in an attempt to assess the efficacy of a newly designed electric toothbrush compared to a conventional manual toothbrush using the American Dental Association's protocol for evaluating toothbrushes. An Oral-B 35 manual toothbrush, which served as the control, was compared to the Plaq & White125 electric toothbrush. Examinations were performed by two calibrated examiners at baseline, day 15 and day 30. Examinations included the gingival index, plaque index and bleeding index. Mean indices were calculated and compared between the two brushes using the repeated measures multiple analysis of variance. No statistically significant differences between the mean indices on the three examination days were observed following the use of the manual or the electric toothbrushes. The results of this study demonstrate that the electric toothbrush was numerically more effective than the manual toothbrush in reducing supragingival plaque levels, either before or after brushing, at each examination date compared to baseline plaque values. However, this difference was not statistically significant. This and other findings concluded that the Plaq & White toothbrush is comparable to the control ADA-accepted toothbrush.     

Norian SRS cement augmentation in hip fracture treatment. Laboratory and initial clinical results

Bone quality, initial fracture displacement, severity of fracture comminution, accuracy of fracture reduction, and the placement of the internal fixation device are important factors that affect fixation stability. New high strength cements that are susceptible to remodeling and replacement for fracture fixation may lead to improved clinical outcome in the treatment of hip fractures. Norian SRS is an injectable, fast setting cement that cures in vivo to form an osteoconductive carbonated apatite of high compressive strength (55 MPa) with chemical and physical characteristics similar to the mineral phase of bone. It can be used as a space filling internal fixation device to facilitate the geometric reconstruction, load transfer, and healing of bone with defects and/or fractures in regions of cancellous bone. Furthermore, this cement can improve the mechanical holding strength of conventional fixation devices. Use of this material potentially could improve fracture stability, retain anatomy during fracture healing and improve hip function, thus achieving better clinical outcomes. In vivo animal studies have shown the material's biocompatibility, and cadaveric studies have shown the biomechanical advantage of its use in hip fractures. Initial clinical experience (in 52 femoral neck fractures and 39 intertrochanteric fractures) showed the potential clinical use of this innovative cement in the treatment of hip fractures.     

Choosing the right clinical camera. Part II

From a practical standpoint, both ring and dual flash are easier to control for the operator. It is not necessary to remember to put the flash on the side of the mirror or to rotate the flash to avoid unwanted shadows. The point source flash requires a learning curve and the dual point source flash, away from the lens, has limited applications. The lighting quality brings out the third dimension in photography and is therefore among the most important factors when taking image quality into consideration. The dual source flash on the lens system provides a more pleasing and natural illumination than the other systems. The Nikon SB21-B fulfills these requirements while offering the possibility to be used as a single source flash unit. Furthermore, the flash unit's close proximity to the lens allows the light to reach virtually any area in the mouth. Lastly, the TTL option takes care of the concern regarding the consistency of the light intensity and significantly speeds up the recycling time.     

Factor-analytic methods of scale development in personality and clinical psychology.

Many clinical and social psychologists need to develop scales to carry out their research. Without adequate training in psychometric methods, they can easily run into difficulty. This article is designed to address some of the more common pitfalls in homogeneous scale construction. Empirical scale development by the criterion-group method is not considered. Suggestions are offered about item writing, answer scale formats, data analysis procedures, and overall scale development strategy. Particular emphasis is placed on the effective use of factor-analytic methods to select items for the scale and to determine its proper location in the hierarchy of factor constructs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)