[Show abstract][Hide abstract] ABSTRACT: Background:
Quantitative microbial risk assessment (QMRA), the current method of choice for evaluating human health risks associated with disease-causing microorganisms, is often constrained by issues such as availability of required data, and inability to incorporate the multitude of factors influencing risk. Bayesian networks (BNs), with their ability to handle data paucity, combine quantitative and qualitative information including expert opinions, and ability to offer a systems approach to characterisation of complexity, are increasingly recognised as a powerful, flexible tool that overcomes these limitations.
We present a QMRA expressed as a Bayesian network (BN) in a wastewater reuse context, with the objective of demonstrating the utility of the BN method in health risk assessments, particularly for evaluating a range of exposure and risk mitigation scenarios. As a case study, we examine the risk of norovirus infection associated with wastewater-irrigated lettuce.
A Bayesian network was developed following a QMRA approach, using published data, and reviewed by domain experts using a participatory process.
Employment of a BN facilitated rapid scenario evaluations, risk minimisation, and predictive comparisons. The BN supported exploration of conditions required for optimal outcomes, as well as investigation of the effect on the reporting nodes of changes in 'upstream' conditions. A significant finding was the indication that if maximum post-treatment risk mitigation measures were implemented, there was a high probability (0.84) of a low risk of infection regardless of fluctuations in other variables, including norovirus concentration in treated wastewater.
BNs are useful in situations where insufficient empirical data exist to satisfy QMRA requirements and they are exceptionally suited to the integration of risk assessment and risk management in the QMRA context. They allow a comprehensive visual appraisal of major influences in exposure pathways, and rapid interactive risk assessment in multifaceted water reuse scenarios.
Science of The Total Environment 10/2015; 541:1393-1409. DOI:10.1016/j.scitotenv.2015.10.030 · 4.10 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: IntroductionTime-consuming manual methods have been required to register cone-beam computed tomography (CBCT) images with plans in the Pinnacle3 treatment planning system in order to replicate delivered treatments for adaptive radiotherapy. These methods rely on fiducial marker (FM) placement during CBCT acquisition or the image mid-point to localise the image isocentre. A quality assurance study was conducted to validate an automated CBCT-plan registration method utilising the Digital Imaging and Communications in Medicine (DICOM) Structure Set (RS) and Spatial Registration (RE) files created during online image-guided radiotherapy (IGRT).MethodsCBCTs of a phantom were acquired with FMs and predetermined setup errors using various online IGRT workflows. The CBCTs, DICOM RS and RE files were imported into Pinnacle3 plans of the phantom and the resulting automated CBCT-plan registrations were compared to existing manual methods. A clinical protocol for the automated method was subsequently developed and tested retrospectively using CBCTs and plans for six bladder patients.ResultsThe automated CBCT-plan registration method was successfully applied to thirty-four phantom CBCT images acquired with an online 0 mm action level workflow. Ten CBCTs acquired with other IGRT workflows required manual workarounds. This was addressed during the development and testing of the clinical protocol using twenty-eight patient CBCTs. The automated CBCT-plan registrations were instantaneous, replicating delivered treatments in Pinnacle3 with errors of ±0.5 mm. These errors were comparable to mid-point-dependant manual registrations but superior to FM-dependant manual registrations.Conclusion
The automated CBCT-plan registration method quickly and reliably replicates delivered treatments in Pinnacle3 for adaptive radiotherapy.
[Show abstract][Hide abstract] ABSTRACT: Bien Hoa Airbase was one of the bulk storage and supply facilities for defoliants during the Vietnam War. Environmental and biological samples taken around the airbase have elevated levels of dioxin. In 2007, a pre-intervention knowledge, attitude and practice (KAP) survey of local residents living in Trung Dung and Tan Phong wards was undertaken regarding appropriate strategies to reduce dioxin exposure. A risk reduction programme was implemented in 2008 and post-intervention KAP surveys were undertaken in 2009 and 2013 to evaluate the longer term impacts. Quantitative assessment was undertaken via a KAP survey in 2013 among 600 local residents randomly selected from the two intervention wards and one control ward (Buu Long). Eight in-depth interviews and two focus group discussions were also undertaken for qualitative assessment. Most programme activities had ceased and dioxin risk communication activities had not been integrated into local routine health education programmes; however, main results generally remained and were better than that in Buu Long. In total, 48.2% of households undertook measures to prevent exposure, higher than those in pre- and post-intervention surveys (25.8% and 39.7%) and the control ward (7.7%). Migration and the sensitive nature of dioxin issues were the main challenges for the programme's sustainability.
Global Public Health 08/2015; DOI:10.1080/17441692.2015.1062904 · 0.92 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Demonstrate the application of decision trees-classification and regression trees (CARTs), and their cousins, boosted regression trees (BRTs)-to understand structure in missing data.
Data taken from employees at 3 different industrial sites in Australia.
7915 observations were included.
The approach was evaluated using an occupational health data set comprising results of questionnaires, medical tests and environmental monitoring. Statistical methods included standard statistical tests and the 'rpart' and 'gbm' packages for CART and BRT analyses, respectively, from the statistical software 'R'. A simulation study was conducted to explore the capability of decision tree models in describing data with missingness artificially introduced.
CART and BRT models were effective in highlighting a missingness structure in the data, related to the type of data (medical or environmental), the site in which it was collected, the number of visits, and the presence of extreme values. The simulation study revealed that CART models were able to identify variables and values responsible for inducing missingness. There was greater variation in variable importance for unstructured as compared to structured missingness.
Both CART and BRT models were effective in describing structural missingness in data. CART models may be preferred over BRT models for exploratory analysis of missing data, and selecting variables important for predicting missingness. BRT models can show how values of other variables influence missingness, which may prove useful for researchers.
Researchers are encouraged to use CART and BRT models to explore and understand missing data.
Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.
BMJ Open 06/2015; 5(6):e007450. DOI:10.1136/bmjopen-2014-007450 · 2.27 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Population pharmacokinetic models combined with multiple sets of age-concentration biomonitoring data facilitate back-calculation of chemical uptake rates from biomonitoring data.
We back-calculated uptake rates of PBDEs for the Australian population from multiple biomonitoring surveys (top-down) and compared them to uptake rates calculated from dietary intake estimates of PBDEs and PBDE concentrations in dust (bottom-up).
Using three sets of PBDE elimination half-lives, we applied a population pharmacokinetic model to the PBDE biomonitoring data measured between 2002/03 and 2010/11 to derive the top-down uptake rates of four key PBDE congeners and six age groups. For the bottom-up approach we used PBDE concentrations measured around 2005.
Top-down uptake rates of ∑4BDE varies from 7.9 to 19 ng/kg/d for toddlers and from 1.2 to 3.0 ng/kg/d for adults; in most cases, they are for all age groups higher than the bottom-up uptake rates. The discrepancy was largest for toddlers with factors up to 7-15 depending on the congener. Despite different elimination half-lives of the four congeners, the age-concentration trends showed no increase in concentration with age and were similar for all congeners.
In the bottom-up approach, PBDE uptake is underestimated; currently known pathways are not sufficient to explain measured PBDE concentrations, especially in young children. While PBDE exposure of toddlers has declined in the past years, pre- and postnatal exposure to PBDEs has remained almost constant because the mothers' PBDE body burden has not yet decreased substantially.
Environmental Health Perspectives 03/2015; 123(10). DOI:10.1289/ehp.1408960 · 7.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Severe dioxin contamination at Bien Hoa and Da Nang airbases, Vietnam is of international concern. Public Health risk reduction programs were implemented in Bien Hoa in 2007-2009 and in Da Nang in 2009-2011. In 2009 and 2011 we reported the encouraging results of these interventions in improving the knowledge, attitude and practices (KAP) of local residents in reducing the dioxin exposure risk through foods. In 2013 we revisited these dioxin hot spots, aimed to evaluate whether the results of the intervention were maintained and to identify factors affecting the sustainability of the programs. To assess this, 16 in-depth interviews, six focus group discussions, and pre and post intervention KAP surveys were undertaken. 800 respondents from six intervention wards and 200 respondents from Buu Long Ward (the control site) were randomly selected to participate in the surveys. The results showed that as of 2013, the programs were rated as "moderately sustained" with a score of 3.3 out of 5.0 (cut off points 2.5 to <3.5) for Bien Hoa, and "well sustained" with a score of 3.8 out of 5.0 (cut off points 3.5 to <4.5) for Da Nang. Most formal intervention program activities had ceased and dioxin risk communication activities were no longer integrated into local routine health education programs. However, the main outcomes were maintained and were better than that in the control ward. Migration, lack of official guidance from City People's Committees and local authorities as well as the politically sensitive nature of dioxin issues were the main challenges for the sustainability of the programs.
Journal of Community Health 12/2014; 40(4). DOI:10.1007/s10900-014-9980-1 · 1.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Contexte
La chimiothérapie à base de cisplatine est de plus en plus le traitement retenu pour les patients atteints du cancer de la tête ou du cancer du cou. La surdité neurosensorielle, important effet secondaire à long terme de la chimioradiothérapie à base de cisplatine, pourrait entraîner une grande détérioration de la qualité de vie des patients traités.
Ce manuscrit avait pour objet d'examiner le mécanisme qui sous-tend la surdité neurosensorielle chez les patients qui subissent des traitements de chimioradiothérapie à base de cisplatine, dont l'incidence de cette affection, l'influence de la radiothérapie et du cisplatine sur celle-ci et l'impact de la toxicité sur la qualité de vie des patients.
Des recherches ont été effectuées dans des bases de données par l'intermédiaire de PubMed (National Centre for Biotechnolgy Information) et d'OvidSP Medline via le site Web de la bibliothèque de la Queensland University of Technology. En outre, des recherches générales d'articles ont été réalisées à l'aide du moteur de recherche en ligne Google Scholar. Les articles dont le contenu intégral n'était pas accessible et ceux qui n'étaient pas en anglais ou qui avaient été publiés avant 1990 ont été rejetés. Les mots-clés utilisés pour les recherches étaient hearing loss, ototoxicity, cancer, quality of life, cisplatin et radiotherapy.
Au total, les recherches ont donné accès à 290 articles. Après un tri basé sur les critères d'exclusion mentionnés ci-dessus, 129 de ces articles ont été jugés appropriés aux fins de l'examen. Il ressort de l'examen que la surdité neurosensorielle est un important effet secondaire à long terme chez les patients qui subissent des traitements de chimioradiothérapie à base de cisplatine. La littérature scientifique courante indique que les effets ototoxiques du cisplatine et l'irradiation crânienne sont considérés comme des entités distinctes; toutefois, il est rare qu'on aborde l'impact des traitements combinés de radiothérapie et de chimiothérapie sur la surdité neurosensorielle. Les facteurs de risque multiples liés à la surdité sont décrits, mais les opinions divergent quant à l'incidence et à la gravité de cet effet ainsi qu'au seuil de dose de rayonnement exact au-delà duquel les traitements combinés de radiothérapie et de chimiothérapie causent la surdité neurosensorielle chez les patients. Cette surdité induit un sous-ensemble de complexités chez les patients atteints du cancer de la tête ou du cancer du cou, qui subissent une importante diminution de leur qualité de vie.
La revue de la littérature réalisée révèle que la surdité neurosensorielle est un important effet secondaire chez les patients atteints du cancer de la tête ou du cancer du cou qui subissent des traitements de chimioradiothérapie à base de cisplatine. Il y a lieu de pousser la recherche afin d'évaluer la contribution de la chimioradiothérapie à base de cisplatine à la surdité neurosensorielle et l'effet ultérieur sur la qualité de vie des patients traités.
Journal of Medical Imaging and Radiation Sciences 09/2014; 45(3). DOI:10.1016/j.jmir.2013.11.003
[Show abstract][Hide abstract] ABSTRACT: Some perfluoroalkyl and polyfluoroalkyl substances (PFASs) have become widespread pollutants detected in human and wildlife samples worldwide. The main objective of this study was to assess temporal trends of PFAS concentrations in human blood in Australia over the last decade (2002-2011), taking into consideration age and sex trends. Pooled human sera from 2002/03 (n=26); 2008/09 (n=24) and 2010/11 (n=24) from South East Queensland, Australia were obtained from de-identified surplus pathology samples and compared with samples collected previously from 2006/07 (n=84). A total of 9775 samples in 158 pools were available for an assessment of PFASs. Stratification criteria included sex and age: <16years (2002/03 only); 0-4 (2006/07, 2008/09, 2010/11); 5-15 (2006/07, 2008/09, 2010/11); 16-30; 31-45; 46-60; and >60years (all collection periods). Sera were analyzed using on-line solid-phase extraction coupled to high-performance liquid chromatography-isotope dilution-tandem mass spectrometry. Perfluorooctane sulfonate (PFOS) was detected in the highest concentrations ranging from 5.3-19.2ng/ml (2008/09) to 4.4-17.4ng/ml (2010/11). Perfluorooctanoate (PFOA) was detected in the next highest concentration ranging from 2.8-7.3ng/ml (2008/09) to 3.1-6.5ng/ml (2010/11). All other measured PFASs were detected at concentrations <1ng/ml with the exception of perfluorohexane sulfonate which ranged from 1.2-5.7ng/ml (08/09) and 1.4-5.4ng/ml (10/11). The mean concentrations of both PFOS and PFOA in the 2010/11 period compared to 2002/03 were lower for all adult age groups by 56%. For 5-15year olds, the decrease was 66% (PFOS) and 63% (PFOA) from 2002/03 to 2010/11. For 0-4year olds the decrease from 2006/07 (when data were first available for this age group) was 50% (PFOS) and 22% (PFOA). This study provides strong evidence for decreasing serum PFOS and PFOA concentrations in an Australian population from 2002 through 2011. Age trends were variable and concentrations were higher in males than in females. Global use has been in decline since around 2002 and hence primary exposure levels are expected to be decreasing. Further biomonitoring will allow assessment of PFAS exposures to confirm trends in exposure as primary and eventually secondary sources are depleted.
Environment International 06/2014; 71C:74-80. DOI:10.1016/j.envint.2014.05.019 · 5.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In images with low contrast-to-noise ratio (CNR), the information gain from
the observed pixel values can be insufficient to distinguish foreground
objects. A Bayesian approach to this problem is to incorporate prior
information about the objects into a statistical model. This paper introduces a
method for representing spatial prior information as an external field in a
hidden Potts model of the image lattice. The prior distribution of the latent
pixel labels is a mixture of Gaussian fields, centred on the positions of the
objects at a previous point in time. This model is particularly applicable in
longitudinal imaging studies, where the manual segmentation of one image can be
used as a prior for automatic segmentation of subsequent images. The model is
demonstrated by application to cone-beam computed tomography (CT), an imaging
modality that exhibits distortions in pixel values due to X-ray scatter. The
external field prior results in a substantial improvement in segmentation
accuracy, reducing the mean pixel misclassification rate on our test images
from 87% to 6%.
[Show abstract][Hide abstract] ABSTRACT: A decision-making framework for image-guided radiotherapy (IGRT) is being developed using a Bayesian Network (BN) to graphically describe, and probabilistically quantify, the many interacting factors that are involved in this complex clinical process. Outputs of the BN will provide decision-support for radiation therapists to assist them to make correct inferences relating to the likelihood of treatment delivery accuracy for a given image-guided set-up correction. The framework is being developed as a dynamic object-oriented BN, allowing for complex modelling with specific subregions, as well as representation of the sequential decision-making and belief updating associated with IGRT. A prototype graphic structure for the BN was developed by analysing IGRT practices at a local radiotherapy department and incorporating results obtained from a literature review. Clinical stakeholders reviewed the BN to validate its structure. The BN consists of a sub-network for evaluating the accuracy of IGRT practices and technology. The directed acyclic graph (DAG) contains nodes and directional arcs representing the causal relationship between the many interacting factors such as tumour site and its associated critical organs, technology and technique, and inter-user variability. The BN was extended to support on-line and off-line decision-making with respect to treatment plan compliance. Following conceptualisation of the framework, the BN will be quantified. It is anticipated that the finalised decision-making framework will provide a foundation to develop better decision-support strategies and automated correction algorithms for IGRT.
Journal of Physics Conference Series 03/2014; 489:012074. DOI:10.1088/1742-6596/489/1/012074
[Show abstract][Hide abstract] ABSTRACT: Cone-beam computed tomography (CBCT) has enormous potential to improve the accuracy of treatment delivery in image-guided radiotherapy (IGRT). To assist radiotherapists in interpreting these images, we use a Bayesian statistical model to label each voxel according to its tissue type. The rich sources of prior information in IGRT are incorporated into a hidden Markov random field model of the 3D image lattice. Tissue densities in the reference CT scan are estimated using inverse regression and then rescaled to approximate the corresponding CBCT intensity values. The treatment planning contours are combined with published studies of physiological variability to produce a spatial prior distribution for changes in the size, shape and position of the tumour volume and organs at risk. The voxel labels are estimated using iterated conditional modes. The accuracy of the method has been evaluated using 27 CBCT scans of an electron density phantom. The mean voxel-wise misclassification rate was 6.2%, with Dice similarity coefficient of 0.73 for liver, muscle, breast and adipose tissue. By incorporating prior information, we are able to successfully segment CBCT images. This could be a viable approach for automated, online image analysis in radiotherapy.
Journal of Physics Conference Series 02/2014; 489(1). DOI:10.1088/1742-6596/489/1/012076
[Show abstract][Hide abstract] ABSTRACT: Brominated flame retardants (BFRs), are chemicals widely used in consumer products including electronics, vehicles, plastics and textiles to reduce flammability. Experimental animal studies have confirmed that these compounds may interfere with thyroid hormone homeostasis and neurodevelopment but to date health effects in humans have not been systematically examined.
To conduct a systematic review of studies on the health impacts of exposure to BFRs in humans, with a particular focus on children.
A systematic review was conducted using the MEDLINE and EMBASE electronic databases up to 1 February 2012. Published cohort, cross-sectional, and case-control studies exploring the relationship between BFR exposure and various health outcomes were included.
In total, 36 epidemiological studies meeting the pre-determined inclusion criteria were included. Plausible outcomes associated with BFR exposure include diabetes, neurobehavioral and developmental disorders, cancer, reproductive health effects and alteration in thyroid function. Evidence for a causal relationship between exposure to BFRs and health outcomes was evaluated within the Bradford Hill framework.
Although there is suggestive evidence that exposure to BFRs is harmful to health, further epidemiological investigations particularly among children, and long-term monitoring and surveillance of chemical impacts on humans are required to confirm these relationships.
[Show abstract][Hide abstract] ABSTRACT: Introduction
Patients with virally mediated head and neck cancer (VMHNC) often present with advanced nodal disease that is highly radioresponsive as demonstrated by tumour and nodal regression during treatment. The resultant changes may impact on the planned dose distribution and so adversely affect the therapeutic ratio. The aim of this study was to evaluate the dosimetric effect of treatment-induced anatomical changes in VMHNC patients who had undergone a replan.
Thirteen patients with virally mediated oropharyngeal or nasopharyngeal cancer who presented for definitive radiotherapy between 2005 and 2010 and who had a replan generated were investigated. The dosimetric effect of anatomical changes was quantified by comparing dose–volume histograms (DVH) of primary and nodal gross target volumes and organs at risk (OAR), including spinal cord and parotid glands, from the original plan and a comparison plan.
Eleven three-dimensional conformal radiation therapy (3DCRT) and two intensity modulated radiation therapy (IMRT) plans were evaluated. Dose to the spinal cord and brainstem increased by 4.1% and 2.6%, respectively. Mean dose to the parotid glands also increased by 3.5%. In contrast, the dose received by 98% of the primary and nodal gross tumour volumes decreased by 0.15% and 0.3%, respectively, when comparing the initial treatment plan to the comparison plan.
In this study, treatment-induced anatomical changes had the greatest impact on OAR dose with negligible effect on the dose to nodal gross tumour volumes. In the era of IMRT, accounting for treatment-induced anatomical changes is important as focus is placed on minimizing the acute and long-term side effects of treatment.