The Wesley Medical Center

Auchenflower, Australia

The Wesley Medical Center

Auchenflower, Australia
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Moutrie V.,Princess Alexandra Hospital | Moutrie V.,University of Wollongong | Kairn T.,The Wesley Medical Center | Rosenfeld A.,University of Wollongong | Charles P.H.,Princess Alexandra Hospital
Australasian Physical and Engineering Sciences in Medicine | Year: 2015

To achieve accurate dose calculations in radiation therapy the electron density of patient tissues must be known. This information is ordinarily gained from a computed tomography (CT) image that has been calibrated to allow relative electron density (RED) to be determined from CT number. When high density objects such as metallic prostheses are involved, direct use of the CT data can become problematic due to the artefacts introduced by high attenuation of the beam. This requires manual correction of the density values, however the properties of the implanted prosthetic are not always known. A method is introduced where the RED of such an object can be determined using the treatment beam of a linear accelerator with an electronic portal imaging device. The technique was tested using a metallic hip replacement that was placed within a container of water. Compared to the theoretical RED of 6.8 for cobalt–chromium alloy, these measurements calculated a value of 6.4 ± 0.7. This would allow the distinction of an implant as Co–Cr or steel, which have similar RED, or titanium, which is much less dense with an RED of 3.7. © 2015, Australasian College of Physical Scientists and Engineers in Medicine.


Charles P.H.,Queensland University of Technology | Crowe S.B.,Queensland University of Technology | Kairn T.,Queensland University of Technology | Kairn T.,the Wesley Medical Center | And 6 more authors.
Journal of Physics: Conference Series | Year: 2014

To obtain accurate Monte Carlo simulations of small radiation fields, it is important model the initial source parameters (electron energy and spot size) accurately. However recent studies have shown that small field dosimetry correction factors are insensitive to these parameters. The aim of this work is to extend this concept to test if these parameters affect dose perturbations in general, which is important for detector design and calculating perturbation correction factors. The EGSnrc C++ user code cavity was used for all simulations. Varying amounts of air between 0 and 2 mm were deliberately introduced upstream to a diode and the dose perturbation caused by the air was quantified. These simulations were then repeated using a range of initial electron energies (5.5 to 7.0 MeV) and electron spot sizes (0.7 to 2.2 FWHM). The resultant dose perturbations were large. For example 2 mm of air caused a dose reduction of up to 31% when simulated with a 6 mm field size. However these values did not vary by more than 2 % when simulated across the full range of source parameters tested. If a detector is modified by the introduction of air, one can be confident that the response of the detector will be the same across all similar linear accelerators and the Monte Carlo modelling of each machine is not required. © Published under licence by IOP Publishing Ltd.


Kairn T.,Queensland University of Technology | Kairn T.,The Wesley Medical Center | Aland T.,The Wesley Medical Center | Franich R.D.,RMIT University | And 9 more authors.
Physics in Medicine and Biology | Year: 2010

This work is focussed on developing a commissioning procedure so that a Monte Carlo model, which uses BEAMnrc's standard VARMLC component module, can be adapted to match a specific Brain LAB m3 micro-multileaf collimator (μMLC). A set of measurements are recommended, for use as a reference against which the model can be tested and optimized. These include radiochromic film measurements of dose from small and offset fields, as well as measurements of μMLC transmission and interleaf leakage. Simulations and measurements to obtain μMLC scatter factors are shown to be insensitive to relevant model parameters and are therefore not recommended, unless the output of the linear accelerator model is in doubt. Ultimately, this note provides detailed instructions for those intending to optimize a VARMLC model to match the dose delivered by their local Brain LAB m3 μMLC device. © 2010 Institute of Physics and Engineering in Medicine Printed in the UK.


Hung Y.-C.,University of Queensland | Bauer J.D.,University of Queensland | Bauer J.D.,The Wesley Research Institute | Horsely P.,The Wesley Hospital | And 4 more authors.
Nutrition | Year: 2014

Objective: The aim of this study was to assess the agreement between detected changes in body composition determined by bioimpedance spectroscopy (BIS) and air-displacement plethysmography (ADP) among patients with cancer undergoing peripheral blood stem cell transplantation (PBSCT); and to assess the agreement of absolute values of BIS with ADP and dual energy x-ray (DXA). Methods: Forty-four adult hematologic cancer patients undergoing PBSCT completed both BIS and ADP assessment at preadmission and at 3 mo after transplantation. A subsample (n = 11) was assessed by DXA at 3 mo after transplantation. Results were examined for the BIS instrument's default setting and three alternative predictive equations from the literature. Agreement was assessed by the Bland-Altman limits of agreement analysis while correlation was examined using the Lin's concordance correlation. Results: Changes in body composition parameters assessed by BIS were comparable with those determined by ADP regardless of the predictive equations used. Bias of change in fat-free mass was clinically acceptable (all <1 kg), although limits of agreement were wide (more than ±6 kg). Overall, the BIS predictive equation accounting for body mass index performed the best. Absolute body composition parameters predicted by the alternative predictive equations agreed with DXA and ADP better than the BIS instrument's default setting. Conclusion: Changes predicted by BIS were similar to those determined by ADP on a group level; however, agreement of predicted changes at an individual level should be interpreted with caution due to wide limits of agreement. © 2014 Elsevier Inc.


Kakakhel M.B.,Pakistan Institute of Engineering and Applied Sciences | Kairn T.,The Wesley Medical Center | Charles P.,Queensland University of Technology | Trapp J.V.,Queensland University of Technology
Journal of Applied Clinical Medical Physics | Year: 2014

This study extends the 'zero scan' method for CT imaging of polymer gel dosimeters to include multislice acquisitions. Multislice CT images consisting of 24 slices of 1.2mm thickness were acquired of an irradiated polymer gel dosimeter and processed with the zero scan technique. The results demonstrate that zero scan-based gel readout can be successfully applied to generate a three-dimensional image of the irradiated gel field. Compared to the raw CT images, the processed figures and cross-gel profiles demonstrated reduced noise and clear visibility of the penumbral region. Moreover, these improved results further highlight the suitability of this method in volumetric reconstruction with reduced CT data acquisition per slice. This work shows that 3D volumes of irradiated polymer gel dosimeters can be acquired and processed with X-ray CT.


Kakakhel M.B.,Queensland University of Technology | Kakakhel M.B.,Pakistan Institute of Engineering and Applied Sciences | Kairn T.,Queensland University of Technology | Kairn T.,The Wesley Medical Center | And 4 more authors.
Physica Medica | Year: 2013

In this study the interplay effects for Enhanced Dynamic Wedge (EDW) treatments are experimentally investigated. Single and multiple field EDW plans for different wedge angles were delivered to a phantom and detector on a moving platform, with various periods, amplitudes for parallel and perpendicular motions. A four field 4D CT planned lung EDW treatment was delivered to a dummy tumor over four fractions. For the single field parallel case the amplitude and the period of motion both affect the interplay resulting in the appearance of a step function and penumbral cut off with the discrepancy worst where collimator-tumor speed is similar. For perpendicular motion the amplitude of tumor motion is the only dominant factor. For large wedge angle the dose discrepancy is more pronounced compared to the small wedge angle for the same field size and amplitude-period values. For a small field size i.e. 5 × 5 cm2 the loss of wedged distribution was observed for both 60° and 15° wedge angles for parallel and perpendicular motions. Film results from 4D CT planned delivery displayed a mix of over and under dosages over 4 fractions, with the gamma pass rate of 40% for the averaged film image at 3%/1 mm DTA (Distance to Agreement). Amplitude and period of the tumor motion both affect the interplay for single and multi-field EDW treatments and for a limited (4 or 5) fraction delivery there is a possibility of non-averaging of the EDW interplay. © 2012 Associazione Italiana di Fisica Medica.


PubMed | The Wesley Medical Center
Type: Journal Article | Journal: Physics in medicine and biology | Year: 2012

The quality assurance of stereotactic radiotherapy and radiosurgery treatments requires the use of small-field dose measurements that can be experimentally challenging. This study used Monte Carlo simulations to establish that PAGAT dosimetry gel can be used to provide accurate, high-resolution, three-dimensional dose measurements of stereotactic radiotherapy fields. A small cylindrical container (4 cm height, 4.2 cm diameter) was filled with PAGAT gel, placed in the parietal region inside a CIRS head phantom and irradiated with a 12-field stereotactic radiotherapy plan. The resulting three-dimensional dose measurement was read out using an optical CT scanner and compared with the treatment planning prediction of the dose delivered to the gel during the treatment. A BEAMnrc/DOSXYZnrc simulation of this treatment was completed, to provide a standard against which the accuracy of the gel measurement could be gauged. The three-dimensional dose distributions obtained from Monte Carlo and from the gel measurement were found to be in better agreement with each other than with the dose distribution provided by the treatment planning systems pencil beam calculation. Both sets of data showed close agreement with the treatment planning systems dose distribution through the centre of the irradiated volume and substantial disagreement with the treatment planning system at the penumbrae. The Monte Carlo calculations and gel measurements both indicated that the treated volume was up to 3 mm narrower, with steeper penumbrae and more variable out-of-field dose, than predicted by the treatment planning system. The Monte Carlo simulations allowed the accuracy of the PAGAT gel dosimeter to be verified in this case, allowing PAGAT gel to be utilized in the measurement of dose from stereotactic and other radiotherapy treatments, with greater confidence in the future.


PubMed | The Wesley Medical Center, University of Queensland and The Wesley Hospital
Type: Comparative Study | Journal: Nutrition (Burbank, Los Angeles County, Calif.) | Year: 2014

The aim of this study was to assess the agreement between detected changes in body composition determined by bioimpedance spectroscopy (BIS) and air-displacement plethysmography (ADP) among patients with cancer undergoing peripheral blood stem cell transplantation (PBSCT); and to assess the agreement of absolute values of BIS with ADP and dual energy x-ray (DXA).Forty-four adult hematologic cancer patients undergoing PBSCT completed both BIS and ADP assessment at preadmission and at 3 mo after transplantation. A subsample (n = 11) was assessed by DXA at 3 mo after transplantation. Results were examined for the BIS instruments default setting and three alternative predictive equations from the literature. Agreement was assessed by the Bland-Altman limits of agreement analysis while correlation was examined using the Lins concordance correlation.Changes in body composition parameters assessed by BIS were comparable with those determined by ADP regardless of the predictive equations used. Bias of change in fat-free mass was clinically acceptable (all <1 kg), although limits of agreement were wide (more than 6 kg). Overall, the BIS predictive equation accounting for body mass index performed the best. Absolute body composition parameters predicted by the alternative predictive equations agreed with DXA and ADP better than the BIS instruments default setting.Changes predicted by BIS were similar to those determined by ADP on a group level; however, agreement of predicted changes at an individual level should be interpreted with caution due to wide limits of agreement.


PubMed | The Wesley Medical Center
Type: Journal Article | Journal: Australasian physical & engineering sciences in medicine | Year: 2011

In response to the clinical need for a dosimetry system with both high resolution and minimal angular dependence, this study demonstrates the utility of Gafchromic EBT2 radiochromic dosimetry film for the quality assurance of micro-collimated IMRT, RapidArc and TomoTherapy treatments. Firstly, preliminary measurements indicated that the dose response of EBT2 film does not appreciably vary with either the angle of incidence of the radiation beam or the depth in water at which the film is placed. Secondly, prostate treatment plans designed for delivery using static-beam IMRT (collimated using the BrainLab m3 microMLC), RapidArc and TomoTherapy were investigated by comparing dose planes obtained from treatment planning calculations with EBT2 film measurements. For all treatment plans, the proportion of dose points agreeing with the film measurements to within (3%,3mm) was found to be above 95%, with all points agreeing within 5%. The film images provided sufficient information to verify that the treatments could be delivered with an acceptable level of accuracy, while also providing additional information on low-level dose variations that were not predicted by the treatment planning systems. This information included: the location and extent of dose from inter-leaf leakage (in the RapidArc plan) and helical field junctioning (in the TomoTherapy plan), as well as the existence of small regions where the treatment planning system under-predicted the dose from very small treatment segments (in the micro-collimated IMRT plan).

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