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Ade N.,University of Witwatersrand | Nam T.L.,University of Witwatersrand | Derry T.E.,University of Witwatersrand | Mhlanga S.H.,Charlotte Maxeke Johannesburg Academic Hospital
Radiation Physics and Chemistry | Year: 2014

Evaluation of the linear response of a radiation detector with absorbed dose rate should be of paramount importance in clinical dosimetry. As modelled by Fowler, electrical conductivity, σ, of a solid-state detector and absorbed dose rate, Dr, are related by σ~Dr δ where δ is the linearity index. The detector is thus independent of dose rate if δ is unity. This contribution investigates and evaluates the dependence of δ of synthetic diamond detectors of various types on therapy electron energy and its influence in relative electron dosimetry with the aim of selecting a suitable crystal. The study was conducted initially on one HPHT and eight CVD synthesised diamonds of optical grade (OG) and detector grade (DG) qualities using 6-14MeV electron therapy beams. For quality control, the diamond specimens were characterised by Raman spectroscopy and electron spin resonance (ESR). Values of δ ranging between 0.79 and 1.03 were obtained for all the nine diamond detectors at 1000V/cm for 7 and 12MeV electron beams. Whereas the δ values of the HPHT diamond were found not to vary with the electron energies, those of three CVD samples of a given class varied with the electron energies within 2%. In addition, a very strong variation of about 9% was observed for two OG crystals of another class. The δ values were found to decrease with increasing dose rate and there was a tendency for the δ values to change with defect levels present within the crystals. Due to the independence of the HPHT diamond[U+05F3]s δ values on electron energy and its better stability of response to radiation, a small-size HPHT crystal was then evaluated of its potential applications in small radiation fields. Relative dose distributions measured with the diamond probe on exposure to 6, 12 and 14MeV electron beams between 1×1cm2 and 10×10cm2 fields were compared with those obtained with reference ion chambers and a Dosimetry Diode E. The results showed that with careful selection of a suitable diamond crystal relative dose distributions taken with the diamond probe would compare favourably with those obtained with the reference detectors within or of the order of 1% with or without dose rate dependence corrections. In addition, the presented results have demonstrated for the CVD diamonds that δ may vary with electron energy and it could be influenced by defect levels. © 2014 Elsevier Ltd. Source


Feldman C.,Charlotte Maxeke Johannesburg Academic Hospital | Feldman C.,University of Witwatersrand | Anderson R.,University of Pretoria | Anderson R.,National Health Laboratory Service
Seminars in Respiratory and Critical Care Medicine | Year: 2012

Community-acquired pneumonia remains an important cause of disease and death in both developed and developing countries and therefore continues to have a major medical impact. The mortality remains high despite the ready availability of potent antimicrobial agents to which the organisms are susceptible. However, management of these infections is potentially complicated by the emerging resistance of many of the common pathogens to the different classes of antibiotics that are usually prescribed. Furthermore, it is also being recognized that antibiotic resistance or treatment failures may occur not only through traditional microbial antibiotic resistance mechanisms but also through less well defined mechanisms, particularly those developed by the microbes in relation to their quorum sensing/biofilm machinery. Much recent research in this field has been focused on evaluating the clinical impact of antibiotic resistance on optimal antibiotic treatment and antimicrobial choices, as well as alternative strategies to deal with antibiotic resistance and treatment failures. Copyright © 2012 by Thieme Medical Publishers, Inc. Source


Kawonga M.,Charlotte Maxeke Johannesburg Academic Hospital
Global health action | Year: 2013

In light of an increasing global focus on health system strengthening and integration of vertical programmes within health systems, methods and tools are required to examine whether general health service managers exercise administrative authority over vertical programmes. To measure the extent to which general health service (horizontal) managers, exercise authority over the HIV programme's monitoring and evaluation (M&E) function, and to explore factors that may influence this exercise of authority. This cross-sectional survey involved interviews with 51 managers. We drew ideas from the concept of 'exercised decision-space' - traditionally used to measure local level managers' exercise of authority over health system functions following decentralisation. Our main outcome measure was the degree of exercised authority - classified as 'low', 'medium' or 'high' - over four M&E domains (HIV data collection, collation, analysis, and use). We applied ordinal logistic regression to assess whether actor type (horizontal or vertical) was predictive of a higher degree of exercised authority, independent of management capacity (training and experience), and M&E knowledge. Relative to vertical managers, horizontal managers had lower HIV M&E knowledge, were more likely to exercise a higher degree of authority over HIV data collation (OR 7.26; CI: 1.9, 27.4), and less likely to do so over HIV data use (OR 0.19; CI: 0.05, 0.84). A higher HIV M&E knowledge score was predictive of a higher exercised authority over HIV data use (OR 1.22; CI: 0.99, 1.49). There was no association between management capacity and degree of authority. This study demonstrates a HIV M&E model that is neither fully vertical nor integrated. The HIV M&E is characterised by horizontal managers producing HIV information while vertical managers use it. This may undermine policies to strengthen integrated health system planning and management under the leadership of horizontal managers. Source


Feldman C.,Charlotte Maxeke Johannesburg Academic Hospital | Feldman C.,University of Witwatersrand | Anderson R.,University of Pretoria
Journal of Infection | Year: 2014

Pneumococcal polysaccharide vaccines (PPVs) and conjugate vaccines (PCVs), of which PPV23 and PCV13 are the current front runners, have had a significant, beneficial impact on public health. With regard to PPV23, there has been some debate, however, about its protective efficacy against all-cause pneumonia, as opposed to invasive pneumococcal disease, in high-risk cases. PCVs, on the other hand, have been included in many national immunisation programmes for prevention of severe pneumococcal disease in infants and young children, as well as for adults in various high-risk categories. Although innovative and effective, the protective efficacy of PCVs, the composition of which is based on the geographic prevalence and virulence of pneumococcal serotypes, is limited due to colonisation of the nasopharynx with non-vaccine serotypes. This phenomenon of serotype replacement has provided the impetus for development of new generation recombinant protein and whole cell pneumococcal vaccines with the potential to provide serotype-independent protection. In addition to an overview of the successes and limitations of PPVs and PCVs, this review is focused on emerging and pipeline protein-based and whole cell vaccines, preceded by a consideration of conserved pneumococcal virulence factors which are potential vaccine candidates. © 2014. Source


Kallenbach T.,Charlotte Maxeke Johannesburg Academic Hospital
Southern African Journal of Anaesthesia and Analgesia | Year: 2015

While beta thalassaemia is not a common disorder with an estimated 100 000 severely affected individuals worldwide, improved survival rates and increased global migration means an increased frequency of such patients being seen for various surgeries. The different aspects of this disorder have wide-ranging implications for anaesthesia. Thus, for safe anaesthetic care, the anaesthetist needs to have a good understanding of beta thalassaemia. Presented here is a case report of a 32-year-old gentleman with beta thalassaemia major presenting for elective laparoscopic cholecystectomy and splenectomy, followed by a discussion of the literature. © 2015 The Author(s). Source

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