Comparison between the TRS-398 code of practice and the TG-51 dosimetry protocol for flattening filter free beams.

Dosimetry protocols for external beam radiotherapy currently in use, such as the IAEA TRS-398 and AAPM TG-51, were written for conventional linear accelerators. In these accelerators, a flattening filter is used to produce a beam which is uniform at water depths where the ionization chamber is used to measure the absorbed dose. Recently, clinical linacs have been implemented without the flattening filter, and published theoretical analysis suggested that with these beams a dosimetric error of order 0.6% could be expected for IAEA TRS-398, because the TPR20,10 beam quality index does not accurately predict the stopping power ratio (water to air) for the softer flattening-filter-free (FFF) beam spectra. We measured doses on eleven FFF linacs at 6 MV and 10 MV using both dosimetry protocols and found average differences of 0.2% or less. The expected shift due to stopping powers was not observed. We present Monte Carlo k Q calculations which show a much smaller difference between FFF and flattened beams than originally predicted. These results are explained by the inclusion of the added backscatter plates and build-up filters used in modern clinical FFF linacs, compared to a Monte Carlo model of an FFF linac in which the flattening filter is removed and no additional build-up or backscatter plate is added.

Trastorno por estrés postraumático (TEPT) en pacientes con traumatismo encéfalo craneano (TEC) / Post-traumatic stress disorder in patients following traumatic brain injury

Introduction: Controversy exists as to whether post-traumatic stress disorder (PTSD) may occur after traumatic brain injury (TBI). Objective: To describe the clinical presentation and course of a group of patients that developed PTSD following a work-related TBI. Methods: Clinical records of patients with PTSD treated in Hospital del Trabajador between years 1987 and 2001 were examined. Those cases in which a TBI had occurred were selected and compared with those in which a TBI had not preceded the PTSD. Results: 32 patients were identified as suffering PTSD preceded by TBI. All patients had suffered mild TBI; 62.5% of them as a result of a traffic accident. On average, patients were referred for mental health consultation 70 days after TBI had occurred, and 31.2% of them received specialized treatment for less than three months. When discharged 25% were asymptomatic. When compared with 453 patients suffering PTSD, with no history of previous TBI, treated during the same period, those who had suffered TBI presented a greater proportion of physical lesions, more prolonged treatment periods, and a greater proportion of them were still symptomatic when discharged. Discussion: In a group of patients suffering PTSD, history of mild TBI was a factor associated with a worse prognosis.

Se ha discutido la aparición del TEPT en pacientes que han presentado un TEC. Aunque algunos autores señalan que ambos diagnósticos no pueden coexistir (ya que la amnesia post TEC impediría el procesamiento de la experiencia traumática), otros refieren que no existen diferencias en cuanto a la frecuencia y clínica del diagnóstico de TEPT al comparar pacientes con y sin TEC. Objetivos: Describir las características clínicas y terapéuticas en un grupo de pacientes accidentados del trabajo que han presentado un TEPT después de un TEC. Método: Se revisaron las fichas clínicas de todos los pacientes con diagnóstico de TEPT entre los años 1987 y 2001, se seleccionaron aquéllas en que el TEPT fue posterior a un TEC y se recolectaron las variables en estudio. Además se compararon los resultados con la población de pacientes con TEPT que no había presentado TEC. Resultados: La muestra estuvo constituida por 32 pacientes con TEC leve (62,5% posterior a un accidente de tránsito). Los pacientes fueron derivados a Salud Mental en promedio a los 70 días del accidente; el tratamiento duró 3 meses o menos en el 31,2% de ellos y sólo el 25% estuvo asintomático al momento del alta. En comparación con un grupo de 453 pacientes con TEPT de diverso origen, los pacientes con TEPT y TEC se caracterizaron por haber sido derivados más tardíamente a salud mental, haber sufrido más accidentes de tránsito, haber presentado más lesiones físicas asociadas y haber requerido un tratamiento más prolongado. Conclusiones: En esta muestra de pacientes con TEPT y TEC este último diagnóstico constituyó un factor de peor pronóstico en la evolución del TEPT.

Fetal cord blood: aspects of heightened immune responses.

Neonatal immune responses have been associated with the development of atopy in childhood. We assessed in cord blood mononuclear cells (CBMC) whether increased allergen/mitogen-induced lymphoproliferation (LP) is associated with pro-allergic Th2 cytokine IL-13 or Th1 cytokine IFN-gamma secretion. We determined whether LP to one allergen is related to heightened lymphocyte function to other allergens/mitogen. CBMC from 135 neonates were stimulated with house dust mite (Derf1), cockroach, ovalbumin, or mitogen. LP to one allergen was associated with significantly increased LP to other allergens/mitogen. Increased Derf1-LP was associated with increased Derf1-induced IL-13 secretion (r = 0.21, p = 0.01). After adjusting for neonatal gender, race, and maternal smoking, Derf1-LP remained associated with Derf1-IL-13 (OR 3.08, 95% CI 1.56-6.10). Increased mitogen-induced proliferation was associated with increased mitogen-induced IL-13 secretion (r = 0.37, p < 0.001). For some individuals, a predisposition to a heightened immune response is already evident at birth. Whether this phenotype results in atopy in childhood warrants further investigation.

Síntomas depresivos posinfarto al miocardio: detección precoz en una población hospitalizada / Depressive symptoms after an acute myocardial infarction

Background: Depression after myocardial infarction (MI) is a frequent disorder and it increases the long-term risk of cardiac mortality. Aim: To assess the frequency of depressive symptoms and the history of depression in hospitalized post-MI patients. Patients and Methods: During three months, depressive symptoms and history of depression were studied in 47 consecutive patients (mean age 59,8±9,5 years, 68 percent male), admitted for MI to the Barros Luco Trudeau Hospital. The Beck Depression Inventory (BDI) and the Composite International Diagnostic Interview (CIDI 2.1) were used with DSM-IV diagnosis criteria. Results: According to the results obtained using the CIDI, 27,7 percent of the patients had a history of depression. This occurred in 53,3 percent of women and 15,6 percent of men (p <0.01). During the hospitalization, 38,3 percent of patients had depressive symptoms (BDI ³ 17 points), affecting 60 percent of women and 28,1 percent of men (p <0.02). In women and patients with history of depression, depressive symptoms tended to be more common and more severe. Conclusions: Depressive symptoms in post-MI patients are frequent and attending physicians should actively detect them.

Response of a tissue equivalent proportional counter to neutrons.

The absorbed dose as a function of lineal energy was measured at the CERN-EC Reference-field Facility (CERF) using a 512-channel tissue equivalent proportional counter (TEPC), and neutron dose equivalent response evaluated. Although there are some differences, the measured dose equivalent is in agreement with that measured by the 16-channel HANDI tissue equivalent counter. Comparison of TEPC measurements with those made by a silicon solid-state detector for low linear energy transfer particles produced by the same beam, is presented. The measurements show that about 4% of dose equivalent is delivered by particles heavier than protons generated in the conducting tissue equivalent plastic.

The influence of neighborhood disadvantage, collective socialization, and parenting on African American children's affiliation with deviant peers.

This study focused on hypotheses about the contributions of neighborhood disadvantage, collective socialization, and parenting to African American children's affiliation with deviant peers. A total of 867 families living in Georgia and Iowa, each with a 10- to 12-year-old child, participated. Unique contributions to deviant peer affiliation were examined using a hierarchical linear model. Community disadvantage derived from census data had a significant positive effect on deviant peer affiliations. Nurturant/involved parenting and collective socialization processes were inversely associated, and harsh/inconsistent parenting was positively associated, with deviant peer affiliations. The effects of nurturant/involved parenting and collective socialization were most pronounced for children residing in the most disadvantaged neighborhoods.

A dynamical model of kinesin-microtubule motility assays.

A two-dimensional stochastic model for the dynamics of microtubules in gliding-assay experiments is presented here, which includes the viscous drag acting on the moving fiber and the interaction with the kinesins. For this purpose, we model kinesin as a spring, and explicitly use parameter values to characterize the model from experimental data. We numerically compute the mean attachment lifetimes of all motors, the total force exerted on the microtubules at all times, the effects of a distribution in the motor speeds, and also the mean velocity of a microtubule in a gliding assay. We find quantitative agreement with the results of J. Howard, A. J. Hudspeth, and R. D. Vale, Nature. 342:154-158. We perform additional numerical analysis of the individual motors, and show how cancellation of the forces exerted by the many motors creates a resultant longitudinal force much smaller than the maximum force that could be exerted by a single motor. We also examine the effects of inhomogeneities in the motor-speeds. Finally, we present a simple theoretical model for microtubules dynamics in gliding assays. We show that the model can be analytically solved in the limit of few motors attached to the microtubule and in the opposite limit of high motor density. We find that the speed of the microtubule goes like the mean speed of the motors in good quantitative agreement with the experimental and numerical results.

The use of 188Re to treat in-stent re-stenosis of coronary arteries.

A pilot study has been conducted in which coronary arteries subject to re-stenosis after angioplasty and stenting have been irradiated following further angioplasty. The method of irradiation has been to use radioactive 188Re in an angioplasty balloon. This paper considers all aspects of the procedure including elution of the rhenium from a tungsten/rhenium generator, its concentration, dispensing and safe delivery to the patient using specially designed equipment to reduce staff doses and radioactive spills. In the pilot study of 28 lesions in 26 patients only 1 was recorded as having angiographic re-stenosis in the treated region at 6 months although 4 other patients had edge re-stenosis. This represents less than 18% re-stenosis in a population that would have been expected to exhibit at least 50% re-stenosis at 6 months. A total of 72 patients have been treated either in the pilot study or a subsequent trial. In only one case has a minor spill of radioactivity occurred and in no case has the balloon burst. Radiation doses to staff are approximately 20 microSv per procedure and are therefore not of serious consequence. It is concluded that this procedure is safe, feasible and effective in reducing in-stent re-stenosis.

Self-esteem, self-serving cognitions, and health risk behavior.

The current article reviews prospective and experimental research on the relation between self-esteem and perceptions of vulnerability. These studies demonstrate that individuals with high self-esteem who engage in risk behavior often utilize a variety of self-serving cognitive strategies that protect them from fully acknowledging their vulnerability to the potential negative consequences of their behavior; e.g., they minimize their estimates of personal risk and overestimate the prevalence of the risk behavior among their peers. The article also provides data on an additional self-serving cognitive strategy employed by adolescents with high self-esteem--alteration of perceptions of others' reactions to their own risk behavior. Finally, the article reviews the emerging literature on the relation between these cognitive strategies and maladaptive health behavior, and proposes that whether these strategies are maladaptive depends on the nature of the threat and the availability of opportunities to engage in compensatory self-enhancement.

Protection and vulnerability processes relevant for early onset of substance use: a test among African American children.

This research tested predictions from a self-regulation model of factors relevant for early onset of tobacco and alcohol use with a community sample of 889 African American children (mean age = 10.5 years). Criterion variables were peer substance use, willingness to use substances, and resistance efficacy (intention to refuse substance offers). Structural modeling indicated effects of temperament dimensions were mediated through self-control and risk-taking constructs, which were related to school involvement, life events, and perceived vulnerability to harmful effects of substances. Peer use was predicted by life events, poor self-control, and parent-child conflict; willingness was predicted by life events, risk taking, and (inversely) parental support; and resistance efficacy was predicted by perceived vulnerability and (inversely) poor self-control. Findings are discussed with reference to theoretical models of early protection and vulnerability processes.

Social comparison as a mediator of response shift.

Previous research in the domain of social comparison theory has suggested that the same factors that have been hypothesized as antecedents to response shift, primarily significant life events, also prompt an increase in interest in social comparison. Based on this research, it is suggested that social comparison, or more specifically, change in social comparison, is a mediator of the relation between significant life events and the change in self-perspective--or response shift--that they often produce. Evidence supporting this claim is reviewed and new data are presented. Finally, the implications of this mediational relation, including those relevant to the design of interventions, are discussed.

The effect of peers' alcohol consumption on parental influence: a cognitive mediational model.

OBJECTIVE: The current study was designed to elucidate familial and social influences on adolescent alcohol consumption by testing three hypotheses derived from the prototype/willingness model of adolescent risk behavior: (1) parents' prototypes of adolescent drinkers affect adolescent consumption through their impact on adolescents' prototypes, (2) strong parent-child relationships are associated with acceptance of parental influence regarding drinking and thus with less adolescent drinking and (3) association with peers who drink dilutes parental influence over adolescents' alcohol consumption. METHOD: Two hundred sixty-six rural adolescents, ages 15 through 17 at Time 1, and their parents and siblings completed questionnaires about drinking behavior and drinking-related cognitions at 1-year intervals for 3 years. RESULTS: Structural equation models provided evidence of transmission of prototypes of adolescent drinkers from parents to adolescents and evidence that these prototypes mediate adolescent alcohol consumption. They also provide evidence that although parents' prototypes and parent-adolescent relationships are important in shaping the adolescents' drinking, association with peers who drink significantly attenuates this influence. CONCLUSIONS: These data suggest that parents can influence their children's drinking, but that this influence has more of an impact if the adolescent is not involved in a drinking-conducive peer environment. The current analyses also suggest that the process of becoming an adolescent drinker involves an active rejection of parents' influence rather than a passive movement away from parents' attitudes and beliefs-a process that is accelerated by association with peers who drink.

Effect of fast duration on disposition of an intraduodenal glucose load in the conscious dog.

UNLABELLED: The effects of prior fast duration (18 h, n = 8; 42 h, n = 8) on the glycemic and tissue-specific responses to an intraduodenal glucose load were studied in chronically catheterized conscious dogs. [3-3H]glucose was infused throughout the study. After basal measurements, glucose spiked with [U-14C]glucose was infused for 150 min intraduodenally. Arterial insulin and glucagon were similar in the two groups. Arterial glucose (mg/dl) rose approximately 70% more during glucose infusion after 42 h than after an 18-h fast. The net hepatic glucose balance (mg. kg-1. min-1) was similar in the two groups (basal: 1.8 +/- 0.2 and 2.0 +/- 0.3; glucose infusion: -2.2 +/- 0.5 and -2.2 +/- 0.7). The intrahepatic fate of glucose was 79% glycogen, 13% oxidized, and 8% lactate release after a 42-h fast; it was 23% glycogen, 21% oxidized, and 56% lactate release after an 18-h fast. Net hindlimb glucose uptake was similar between groups. The appearance of intraduodenal glucose during glucose infusion (mg/kg) was 900 +/- 50 and 1,120 +/- 40 after 18- and 42-h fasts (P < 0.01). CONCLUSION: glucose administration after prolonged fasting induces higher circulating glucose than a shorter fast (increased appearance of intraduodenal glucose); liver and hindlimb glucose uptakes and the hormonal response, however, are unchanged; finally, an intrahepatic redistribution of carbons favors glycogen deposition.

Individual differences in social comparison: development of a scale of social comparison orientation.

Development and validation of a measure of individual differences in social comparison orientation (the Iowa-Netherlands Comparison Orientation Measure [INCOM]) are described. Assuming that the tendency toward social comparison is universal, the scale was constructed so as to be appropriate to and comparable in 2 cultures: American and Dutch. It was then administered to several thousand people in each country. Analyses of these data are presented indicating that the scale has good psychometric properties. In addition, a laboratory study and several field studies are described that demonstrated the INCOM's ability to predict comparison behavior effectively. Possible uses of the scale in basic and applied settings are discussed.

The effect of risk communication on risk perceptions: the significance of individual differences.

The purpose of this paper is to address the literature on the relation between risk communication and the initiation of health behavior change. More specifically, we examine the evidence that providing risk information is an effective way to change risk perceptions, as well as the more limited evidence that altering risk perceptions influences risk behavior. The paper discusses significant developments in the research on these issues, describes specific studies that represent trends in this research, and discusses methodologic issues important to the development of the field. Although there are relatively few studies that demonstrate causal links between risk communication and behavior change, recent developments in the field point to the importance of tailoring risk communications to the individual characteristics of targets. Such tailoring has taken a variety of forms, including providing individualized feedback concerning risk status or genetic vulnerability and assessing readiness for behavior change. Future intervention efforts should combine individualized risk status feedback with assessment of individual differences in previous behavior and acceptance of personal vulnerability.

Enhanced muscle glucose uptake facilitates nitrogen efflux from exercised muscle.

The hypothesis that glucose ingestion in the postexercise state enhances the synthesis of glutamine and alanine in the skeletal muscle was tested. Glucose was infused intraduodenally for 150 min (44.5 micromol . kg-1 . min-1) beginning 30 min after a 150-min period of exercise (n = 7) or an equivalent duration sedentary period (n = 10) in 18-h-fasted dogs. Prior exercise caused a twofold greater increase in limb glucose uptake during the intraduodenal glucose infusion compared with uptake in sedentary dogs. Arterial glutamine levels fell gradually with the glucose load in both groups. Net hindlimb glutamine efflux increased in response to intraduodenal glucose in exercised but not sedentary dogs (P < 0. 05-0.01). Arterial alanine levels, depleted by 50% with exercise, rose with intraduodenal glucose in exercised but not sedentary dogs (P < 0.05-0.01). Net hindlimb alanine efflux also rose in exercised dogs in response to intraduodenal glucose (P < 0.05-0.01), whereas it was not different from baseline in sedentary controls for the first 90 min of glucose infusion. Beyond this point, it, too, rose significantly. We conclude that oral glucose may facilitate recovery of muscle from prolonged exercise by enhancing the removal of nitrogen in the form of glutamine and alanine.

Reasoned action and social reaction: willingness and intention as independent predictors of health risk.

Three studies are described that assess elements of a new model of adolescent health-risk behavior, the prototype/willingness (P/W) model (F. X. Gibbons & M. Gerrard, 1995, 1997). The 1st analysis examined whether a central element of the prototype model, behavioral willingness, adds significantly to behavioral expectation in predicting adolescents' smoking behavior. The 2nd set of analyses used structural-equation-modeling procedures to provide the 1st test of the complete model in predicting college students' pregnancy-risk behavior. Finally, the 3rd study used confirmatory factor analysis to assess the independence of elements of the model from similar elements in other health behavior models. Results of the 3 studies provided support for the prototype model and, in particular, for 2 of its primary contentions: (a) that much adolescent health-risk behavior is not planned and (b) that willingness and intention are related but independent constructs, each of which can be an antecedent to risk behavior.

Self-esteem and the relation between risk behavior and perceptions of vulnerability to unplanned pregnancy in college women.

This article reports 2 studies testing the hypothesis that individuals with high self-esteem are more likely than those with low self-esteem to interpret information about their personal vulnerability to health risks in a self-serving manner. Study 1 used an experimental paradigm to demonstrate that self-esteem moderates the influence of review of sexual and contraceptive behavior on college women's perceptions of vulnerability to unplanned pregnancy (N = 125). Study 2 used a longitudinal design to demonstrate that self-esteem also moderates the relation between naturally occurring changes in college women's sexual behavior and changes in their risk perception (N = 273). Together, these studies provide evidence that people with high self-esteem use self-serving cognitive strategies to maintain their risk perceptions.

Cognitive reactions to smoking relapse: the reciprocal relation between dissonance and self-esteem.

Perceptions of health risk associated with smoking, commitment to quitting, and self-concept were assessed among smokers before, during, and after their participation in cessation clinics. Consistent with expectations derived from cognitive dissonance theory, results indicated that relapsers' perception of risk declined after they resumed smoking, although the decline was significant only for relapsers with high self-esteem; high self-esteem relapsers experienced a significantly greater decline in commitment to quitting than did low self-esteem relapsers; and decline in risk perception among relapsers was associated with maintenance of self-esteem. The implications of these results for dissonance theory and the study of smoking relapse and cessation are discussed.

Smoker networks and the "typical smoker": a prospective analysis of smoking cessation.

Perceptions of the typical smoker (i.e., prototype) were assessed in a sample of 174 adult smokers when they first joined a cessation clinic and were used to predict smoking status at 6-month follow-up. As predicted, consistent with a prototype-based model of health risk behavior (F. X. Gibbons & M. Gerrard, 1995, in press), smokers with more favorable perceptions were more likely to have relapsed at follow-up. Also as predicted, this prospective effect was moderated by smokers' social networks: Prototypes did not predict status among those who had a lot of friends and family members who smoked, suggesting that these other smokers were inhibiting smokers' attempts to distance themselves psychologically from the prototype. Implications of the results for interventions that use prototypes to discourage smoking are discussed.