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New Lambton, Australia

Fuangrod T.,University of Newcastle | Rowshanfarzad P.,University of Western Australia | Greer P.B.,University of Newcastle | Greer P.B.,Hunter Region Mail Center | Middleton R.H.,University of Newcastle
Physica Medica

A new tool with the potential to verify and track jaw position during delivery has been developed. The method should be suitable for independent quality assurance for jaw position during jaw tracking dynamic IMRT and VMAT treatments. The jaw detection and tracking algorithm developed consists of five main steps. Firstly, the image is enhanced by removing a normalised predicted EPID image (that does not include the collimator transmission) from each cine EPID image. Then, using a histogram clustering technique a global intensity threshold level was determined. This threshold level was used to classify each pixel of the image as either under the jaws or under the MLC. Additionally, the collimator angle was automatically detected and used to rotate the image to vertical direction. Finally, this rotation allows the jaw positions to be determined using vertical and horizontal projection profiles. Nine IMRT fields (with static jaws) and a single VMAT clinical field (with dynamic jaws) were tested by determining the root mean square difference between planned and detected jaw positions. The test results give a detection accuracy of ±1mm RMS error for static jaw IMRT treatments and ±1.5mm RMS error for the dynamic jaw VMAT treatment. This method is designed for quality assurance and verification in modern radiation therapy; to detect the position of static jaws or verify the position of tracking jaws in more complex treatments. This method uses only information extracted from EPID images and it is therefore independent from the linear accelerator. © 2014 Associazione Italiana di Fisica Medica. Source

Cox M.B.,Hunter Medical Research Institute | Ban M.,University of Cambridge | Bowden N.A.,Hunter Medical Research Institute | Baker A.,University of Cambridge | And 3 more authors.
Multiple Sclerosis Journal

Background: The environmental influence of sun exposure and vitamin D in particular and its implication with multiple sclerosis (MS) has recently received considerable attention. Current evidence based on genetic and epidemiological studies indicate that vitamin D is implicated in the aetiology of this disease.Methods: We examined two common variants in the vitamin D receptor (VDR) gene in 1153 trio families and 726 cases and 604 controls. We also examined epistatic interactions between the VDR SNPs rs731236 and rs2228570 with the tagging single nucleotide polymorphism (SNP) rs3135388 for the HLA-DRB*1501 locus containing a highly conserved vitamin D responsive element within its promoter region.Results: We found weak evidence for an association between the rs731236C allele and MS, while there was no direct association with rs2228570. When examining the interaction between the VDR gene variations and the DRB1*1501 tagging SNP a more complex relationship was observed. Although the interaction was not statistically significant, there appeared to be a trend of increasing risk of MS in participants who were homozygous for the HLA-DRB1*1501 allele in association with the more active form of the VDR (Fok1).Conclusion: We have identified weak evidence of an association between a common variation within the VDR gene and MS, in the largest study reported to date of this candidate gene. There appears to be a relationship between polymorphisms in the VDR and the risk of MS, which is potentially modified by HLA-DRB1*1501. © SAGE Publications 2012. Source

Acquisition of teleseismic data in south-western New South Wales during 2007 formed the latest stage of a rolling deployment of seismometers over south-eastern Australia, and allowed a revised tomographic model to be constructed for the lithospheric mantle under Victoria and southern NSW. Our aim here is to link the observed distribution of upper-mantle P-wave velocity to the major geological features of the upper crust, which here comprise terranes of the Delamerian and Lachlan orogens. We have extended the definition of the boundaries of these terranes under cover by the use of the tilt-filter of total magnetic intensity, which provides an image with detailed resolution for sources at depths down to ∼5km. We proceed to infer the distribution of deeper sources in the middle and lower crust by two approaches to the use of potential-field images: we exploit the relationship between wavenumber and source depth, through the application of a 20-km low-pass filter to the total magnetic intensity grid; and we take advantage of the lower sensitivity of gravity anomalies to depth of source, compared to magnetic anomalies with dipolar sources, by defining broad features in the isostatic gravity grid. Our interpretation of the low-pass magnetic and isostatic gravity imagery confirms the relationship between high mantle velocity and the Proterozoic Delamerian Orogen, and indicates that a salient of high mantle velocity under the Palaeozoic Stawell Zone results from an underthrust wedge of Delamerian basement. High mantle velocity under the Palaeozoic Wagga-Omeo Zone may be a result of lithospheric thickening that is a corollary of mid- to lower crustal thrust faulting indicated by the potential field data. Low mantle velocity under part of the Melbourne Zone may result from thermochemical resetting of its Proterozoic microcontinental basement by the thermal event responsible for the extensive Cainozoic volcanism in western Victoria; low mantle velocity under the Hay-Booligal Zone, which also appears to be anomalous, may similarly be related to a heat pulse that engendered the swarm of diatremes that is distributed across the zone. © ASEG 2010. Source

Woodruff H.C.,University of Newcastle | Fuangrod T.,University of Newcastle | Rowshanfarzad P.,University of Newcastle | McCurdy B.M.C.,Cancercare Manitoba | And 3 more authors.
Medical Physics

Purpose: Pretreatment verification of volumetric modulated arc therapy (VMAT) dose delivery with electronic portal imaging device (EPID) uses images integrated over the entire delivery or over large subarcs. This work aims to develop a new method for gantry-angle-resolved verification of VMAT dose delivery using EPID. Methods: An EPID dose prediction model was used to calculate EPID images as a function of gantry angle for eight prostate patient deliveries. EPID image frames at 7.5 frames per second were acquired during delivery via a frame-grabber system. The gantry angle for each image was encoded in kV frames which were synchronized to the MV frames. Gamma analysis results as a function of gantry angle were assessed by integrating the frames over 2°subarcs with an angle-to-agreement tolerance of 0.5°about the measured image angle. Results: The model agreed with EPID images integrated over the entire delivery with average Gamma pass-rates at 2%, 2 mm of 99.7% (10% threshold). The accuracy of the kV derived gantry angle for each image was found to be 0.1°(1 SD) using a phantom test. For the gantry-resolved analysis all Gamma pass-rates were greater than 90% at 3%, 3 mm criteria (with only two exceptions), and more than 90% had a 95% pass-rate, with an average of 97.3%. The measured gantry angle lagged behind the predicted angle by a mean of 0.3°± 0.3°, with a maximum lag of 1.3°. Conclusions: The method provides a comprehensive and highly efficient pretreatment verification of VMAT delivery using EPID. Dose delivery accuracy is assessed as a function of gantry angle to ensure accurate treatment. © 2013 American Association of Physicists in Medicine. Source

Pretto J.J.,Hunter Region Mail Center | Pretto J.J.,University of Newcastle | Roebuck T.,Alfred Sleep Disorders and Ventilatory Failure Service | Beckert L.,Canterbury District Health Board | And 3 more authors.

Pulse oximetry provides a simple, non-invasive approximation of arterial oxygenation in a wide variety of clinical settings including emergency and critical-care medicine, hospital-based and ambulatory care, perioperative monitoring, inpatient and outpatient settings, and for specific diagnostic applications. Pulse oximetry is of utility in perinatal, paediatric, adult and geriatric populations but may require use of age-specific sensors in these groups. It plays a role in the monitoring and treatment of respiratory dysfunction by detecting hypoxaemia and is effective in guiding oxygen therapy in both adult and paediatric populations. Pulse oximetry does not provide information about the adequacy of ventilation or about precise arterial oxygenation, particularly when arterial oxygen levels are very high or very low. Arterial blood gas analysis is the gold standard in these settings. Pulse oximetry may be inaccurate as a marker of oxygenation in the presence of dyshaemoglobinaemias such as carbon monoxide poisoning or methaemoglobinaemia where arterial oxygen saturation values will be overestimated. Technical considerations such as sensor position, signal averaging time and data sampling rates may influence clinical interpretation of pulse oximetry readings. © 2013 The Authors. Respirology © 2013 Asian Pacific Society of Respirology. Source

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