Monte Carlo calculations of electron beam output factors for a medical linear accelerator

The purpose of this study was to investigate the application of the Monte Carlo technique to the calculation and analysis of output factors for electron beams used in radiotherapy. The code EGS4/BEAM was used to obtain phase-space files for 6, 12 and 20 MeV clinical electron beams from a scattering-foil linac (Varian Clinac 2100C) for a clinically representative range of applicator and square or rectangular insert combinations. The source-to-surface distance used was 100 cm. The field sizes ranged from 1 x 1 cm2 to 20 x 20 cm2. These phase-space files were analysed to study the intrinsic beam characteristics and used as source input for relative dose and output factor computations in homogeneous water phantoms using the code EGS4/DOSXYZ. The calculated relative central-axis depth-dose and transverse dose profiles at various depths of clinical interest agreed with the corresponding measured dose profiles to within 2% of the maximum dose. Calculated output factors for the fields studied agreed with measured output factors to about 2%. This demonstrated that for the Varian Clinac 2100C linear accelerator, electron beam dose calculations in homogeneous water phantoms can be performed accurately at the 2% level using Monte Carlo simulations.     

Energy and dose rate dependence of a diamond detector in the dosimetry of 4-25 MV photon beams

Motion of the left ventricular cavity center during the cardiac cycle was compared using transthoracic and intracardiac echocardiography. Rotation was comparable for the 2 methods, however, translation of the left ventricular cavity area center was greater with intracardiac echocardiography.     

Receiving support as a mixed blessing: Evidence for dual effects of support on psychological outcomes.

Although social support is thought to boost feelings of closeness in dyadic relationships, recent findings have suggested that support receipt can increase distress in recipients. The authors investigated these apparently contrary findings in a large daily diary study of couples over 31 days leading up to a major stressor. Results confirm that daily support receipt was associated with greater feelings of closeness and greater negative mood. These average effects, however, masked substantial heterogeneity. In particular, those recipients showing greater benefits on closeness tended to show lesser cost on negative mood, and vice versa. Self-esteem was examined as a possible moderator of support effects, but its role was evident in only a subset of recipients. These results imply that models of dyadic support processes must accord a central role to between-individual heterogeneity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

TWIP950在某新车型前纵梁的应用可行性研究

本文对第二代AHSS典型钢种TWIP950的机械性能包括拉伸强度、n值、r值和烘烤硬化性进行了试验.采用1.5 mm厚度TWIP950替代1.6 mm厚度DC05进行轻量化设计的前纵梁正碰仿真结果表明,使用TWIP钢在减重6.25%的同时具有更佳的吸能效果.通过冲压仿真和现场试制对两种材料的冲压成形性进行了比较,结果表明TWIP950在具有更好成形性的同时也面临更大的回弹.总之,在模具设计时进行有效的回弹控制并保证钢板理想的边缘状态,TWIP950具备在前纵梁的轻量化应用可行性.     

Low energy X-ray depth dose data for use in radiotherapy--comments on the review of BJR Supplement 17

Percentage depth dose data acquired during the revision of BJR Supplement 17: Central Axis Depth Dose Data for Use in Radiotherapy have been reviewed. Coverage of the half value layer (HVL) and field diameter rang was broad, although gaps were apparent at HVLs of 3-5 and 6-7 mm A1 and field diameters > 14 cm. Comparisons of submitted data with that in Supplement 17 indicate a generally even spread of data about the existing PDD values. Most data agreed to within +/- 5% at 2 cm and +/- 15% at 10 cm depth. Systematic discrepancies may be due to the use of different phantom materials. There is evidence that the spread of data is at least partially due to the problems of beam quality specification. The inadequacy of the first HVL as a specifier of beam quality is a well known and a more realistic specifier might be defined in terms of a broad beam dose ratio at defined depths, for a given beam geometry.     

Evidence for cAMP-independent mechanisms mediating the effects of adrenomedullin, a new inotropic peptide

OBJECTIVE: To determine the relation of skeletal body build and obesity to blood pressure and the prevalence of hypertension. DESIGN: Cross-sectional data obtained from the baseline recruitment of the EPIC-Potsdam Study, which is part of the European Prospective Investigation into Cancer and Nutrition (EPIC). SUBJECTS: A total of 10,303 subjects (4387 men, aged 40-65 y and 5916 women, aged 35-65 y) were recruited between January 1995 and July 1996. MEASUREMENTS: Anthropometric measures included body mass index (BMI), waist-hip ratio (WHR) and metrik index (MIX) as a measure of body build that is derived from the relation of chest depth and breadth to body height. Systolic and diastolic blood pressure was obtained using automatic oscillometric devices. Hypertension was defined as blood pressure > or = 160/95 mmHg or current use of antihypertensive medication. Information on lifestyle factors were obtained by personal interview. STATISTICAL ANALYSIS: Logistic regression was used to define the association of categories of BMI, WHR, and MIX and the prevalence of hypertension. Odds ratios (ORs) of being hypertensive were estimated comparing the highest to the lowest quintile, adjusting for age, smoking status, alcohol intake level, educational attainment, physical activity categories, and each of the anthropometric variables. RESULTS: The simultaneously adjusted OR of being hypertensive, comparing the highest vs the lowest category, was for BMI 2.3 (95% confidence interval (CI) = 1.6-3.2) in men and 1.8 (95% CI = 1.4-2.5) in women, for WHR 1.8 (95% CI = 1.4-2.4) in men and 1.5 (95% CI = 1.2-2.0) in women, and for MIX (largest chest size vs lowest chest size relative to body height) 2.0 (95% CI = 1.4-2.8) in men and 2.2 (95% CI = 1.6-3.1) in women. CONCLUSION: In addition to measures of overall obesity (BMI) as well as central obesity (WHR), skeletal body build (MIX) was independently associated with the prevalence of hypertension. The biological mechanism relating MIX to hypertension, however, is still unclear and needs further exploration.     

Serotonin axons of the neostriatum show a higher affinity for striatal than for ventral mesencephalic transplants: a quantitative study in adult and immature recipient rats

Tight junctions (TJ) govern ion and solute diffusion through the paracellular space (gate function), and restrict mixing of membrane proteins and lipids between membrane domains (fence function) of polarized epithelial cells. We examined roles of the RhoA and Rac1 GTPases in regulating TJ structure and function in MDCK cells using the tetracycline repressible transactivator to regulate RhoAV14, RhoAN19, Rac1V12, and Rac1N17 expression. Both constitutively active and dominant negative RhoA or Rac1 perturbed TJ gate function (transepithelial electrical resistance, tracer diffusion) in a dose-dependent and reversible manner. Freeze-fracture EM and immunofluoresence microscopy revealed abnormal TJ strand morphology and protein (occludin, ZO-1) localization in RhoAV14 and Rac1V12 cells. However, TJ strand morphology and protein localization appeared normal in RhoAN19 and Rac1N17 cells. All mutant GTPases disrupted the fence function of the TJ (interdomain diffusion of a fluorescent lipid), but targeting and organization of a membrane protein in the apical membrane were unaffected. Expression levels and protein complexes of occludin and ZO-1 appeared normal in all mutant cells, although ZO-1 was more readily solubilized from RhoAV14-expressing cells with Triton X-100. These results show that RhoA and Rac1 regulate gate and fence functions of the TJ, and play a role in the spatial organization of TJ proteins at the apex of the lateral membrane.     

Evidence for higher reaction time variability for children with ADHD on a range of cognitive tasks including reward and event rate manipulations.

Objective: The purpose of the research study was to examine the manifestation of variability in reaction times (RT) in children with attention deficit hyperactivity disorder (ADHD) and to examine whether RT variability presented differently across a variety of neuropsychological tasks, was present across the two most common ADHD subtypes, and whether it was affected by reward and event rate (ER) manipulations. Method: Children with ADHD-combined type (n = 51), ADHD-predominantly inattentive type (n = 53), and 47 controls completed five neuropsychological tasks (Choice Discrimination Task, Child Attentional Network Task, Go/No-Go task, Stop Signal Task, and N-back task), each allowing trial-by-trial assessment of RTs. Multiple indicators of RT variability including RT standard deviation, coefficient of variation and ex-Gaussian tau were used. Results: Children with ADHD demonstrated greater RT variability than controls across all five tasks as measured by the ex-Gaussian indicator tau. There were minimal differences in RT variability across the ADHD subtypes. Children with ADHD also had poorer task accuracy than controls across all tasks except the Choice Discrimination task. Although ER and reward manipulations did affect children's RT variability and task accuracy, these manipulations largely did not differentially affect children with ADHD compared to controls. RT variability and task accuracy were highly correlated across tasks. Removing variance attributable to RT variability from task accuracy did not appreciably affect between-groups differences in task accuracy. Conclusions: High RT variability is a ubiquitous and robust phenomenon in children with ADHD. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The risk of acute leukemia in patients treated for Hodgkin's disease is significantly higher aft [see bined modality programs than after chemotherapy alone and is correlated with the extent of radiotherapy and type and duration of chemotherapy: a case-control study

BACKGROUND AND OBJECTIVE: Patients treated for Hodgkin's disease have an increased risk of developing subsequent acute leukemia. This co-operative study was conducted to assess the relative risk associated with several candidate factors including age, splenectomy, combined modality therapy and cumulative drug dose including alkylating agents and nitrosurea derivatives. DESIGN AND METHODS: This study evaluated the risk of acute leukemia according to pretreatment variables and therapy modalities among 1659 patients treated for Hodgkin's disease and followed for a median time of 10 years. Both case-control and actuarial risk studies were performed. Median age was 34 years (range: 12-83); 53% of patients were splenectomized. As to the overall therapy, 348 patients (21%) were given radiotherapy (RT) alone, 375 (23%) chemotherapy (CT) alone (including MOPP, MOPP + ABVD or MOPP + ABVD + lomustine); 936 (56%) received both CT and RT, either as primary or salvage treatment. RESULTS: The overall 15-year actuarial risk of leukemia was 4.2%; the hazard function curve showed two peaks of risk at the 3th and the 8th year from the initiation of therapy and no leukemia beyond the 12th year of follow-up. Risk of leukemia was 0.3% after RT alone, 2.8% after CT alone (2.2% after MOPP; 4.4% after MOPP + ABVD + lomustine), and 5.4% in patients given combined modality therapy (10.2% for RT + MOPP; 15.6% for RT + MOPP + lomustine). No leukemia occurred after ABVD alone and the risk was low (0.6%) when neither mechlorethamine nor lomustine were utilized. Patients who had received extended radiotherapy including abdomen and pelvis in addition to MOPP showed a significantly higher risk of leukemia compared to those given limited RT + MOPP (P = 0.01). Case-control analysis indicated advanced stage, type and duration (> 8 months) of CT and extension of RT as significant risk factors for leukemia. Compared to RT alone, the odds ratio was 5.9 after MOPP + extended RT, and 8 when a lomustine-containing regimen was used, as well. Neither age nor splenectomy were independent risk factors for leukemia; splenectomy was influential only when patients had been given MOPP chemotherapy, as well. INTERPRETATIONS AND CONCLUSIONS: Both case-control and actuarial analyses indicated that: a) combined modality therapy with MOPP and extensive RT (including abdomen and pelvis), and the use of lomustine added to the leukemogenic risk of MOPP alone; b) programs without mechlorethamine, procarbazine and lomustine were almost devoid of leukemogenic risk.