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Wollongong, Australia

Yu P.,University of Wollongong | Gandhidasan S.,Wollongong Hospital | Miller A.A.,Illawarra Cancer Care Center
International Journal of Medical Informatics | Year: 2010

Background and purpose: The experience of clinicians at two public hospitals in Sydney, Australia, with the introduction and use of an oncology information system (OIS) was examined to extract lessons to guide the introduction of clinical information systems in public hospitals. Methods and materials: Semi-structured interviews were conducted with 12 of 15 radiation oncologists employed at the two hospitals. The personnel involved in the decision making process for the introduction of the system were contacted and their decision making process revisited. The transcribed data were analyzed using NVIVO software. Themes emerged included implementation strategies and practices, the radiation oncologists' current use and satisfaction with the OIS, project management and the impact of the OIS on clinical practice. Results: The hospitals had contrasting experiences in their introduction and use of the OIS. Hospital A used the OIS in all aspects of clinical documentation. Its implementation was associated with strong advocacy by the Head of Department, input by a designated project manager, and use and development of the system by all staff, with timely training and support.With no vision of developing a paperless information system, Hospital B used the OIS only for booking and patient tracking. A departmental policy that data entry for the OIS was centrally undertaken by administrative staff distanced clinicians from the system. All the clinicians considered that the OIS should continuously evolve to meet changing clinical needs and departmental quality improvement initiatives. Conclusions: This case study indicates that critical factors for the successful introduction of clinical information systems into hospital environment were an initial clear vision to be paperless, strong clinical leadership and management at the departmental level, committed project management, and involvement of all staff, with appropriate training. Clinician engagement is essential for post-adoption evolution of clinical information systems. © 2010 Elsevier Ireland Ltd. Source

Oborn B.M.,Illawarra Cancer Care Center | Metcalfe P.E.,Illawarra Cancer Care Center | Butson M.J.,University of Wollongong | Rosenfeld A.B.,Illawarra Cancer Care Center | Keall P.J.,University of Sydney
Medical Physics | Year: 2012

Purpose: In recent times, longitudinal field MRI-linac systems have been proposed for 6 MV MRI-guided radiotherapy (MRIgRT). The magnetic field is parallel with the beam axis and so will alter the transport properties of any electron contamination particles. The purpose of this work is to provide a first investigation into the potential effects of the MR and fringe magnetic fields on the electron contamination as it is transported toward a phantom, in turn, providing an estimate of the expected patient skin dose changes in such a modality. Methods: Geant4 Monte Carlo simulations of a water phantom exposed to a 6 MV x-ray beam were performed. Longitudinal magnetic fields of strengths between 0 and 3 T were applied to a 30 30 20 cm 3 phantom. Surrounding the phantom there is a region where the magnetic field is at full MRI strength, consistent with clinical MRI systems. Beyond this the fringe magnetic field entering the collimation system is also modeled. The MRI-coil thickness, fringe field properties, and isocentric distance are varied and investigated. Beam field sizes of 5 5, 10 10, 15 15 and 20 20 cm 2 were simulated. Central axis dose, 2D virtual entry skin dose films, and 70 m skin depth doses were calculated using high resolution scoring voxels. Results: In the presence of a longitudinal magnetic field, electron contamination from the linear accelerator is encouraged to travel almost directly toward the patient surface with minimal lateral spread. This results in a concentration of electron contamination within the x-ray beam outline. This concentration is particularly encouraged if the fringe field encompasses the collimation system. Skin dose increases of up to 1000 were observed for certain configurations and increases above Dmax were common. In nonmagnetically shielded cases, electron contamination generated from the jaw faces and air column is trapped and propagated almost directly to the phantom entry region, giving rise to intense dose hot spots inside the x-ray treatment field. These range up to 1000 or more of Dmax at the CAX, depending on field size, isocenter, and coil thickness. In the case of a fully magnetically shielded collimation system and the lowest MRI field of 0.25 T, the entry skin dose is expected to increase to at least 40, 50, 65, and 80 of Dmax for 5 5, 10 10, 15 15, and 20 20 cm 2, respectively. Conclusions: Electron contamination from the linac head and air column may cause considerable skin dose increases or hot spots at the beam central axis on the entry side of a phantom or patient in longitudinal field 6 MV MRIgRT. This depends heavily on the properties of the magnetic fringe field entering the linac beam collimation system. The skin dose increase is also related to the MRI-coil thickness, the fringe field, and the isocenter distance of the linac. The results of this work indicate that the properties of the MRI fringe field, electron contamination production, and transport must be considered carefully during the design stage of a longitudinal MRI-linac system. © 2012 American Association of Physicists in Medicine. Source

Gargett M.,University of Wollongong | Oborn B.,University of Wollongong | Oborn B.,Illawarra Cancer Care Center | Metcalfe P.,University of Wollongong | And 2 more authors.
Medical Physics | Year: 2015

Purpose: MRI-guided radiation therapy systems (MRIgRT) are being developed to improve onlineimaging during treatment delivery. At present, the operation of single point dosimeters and anionization chamber array have been characterized in such systems. This work investigates a novel 2Ddiode array, named magic plate, for both single point calibration and 2D positional performance, thelatter being a key element of modern radiotherapy techniques that will be delivered by these systems.Methods: GEANT 4 Monte Carlo methods have been employed to study the dose response of a silicondiode array to 6 MV photon beams, in the presence of in-line and perpendicularly aligned uniformmagnetic fields. The array consists of 121 silicon diodes (dimensions 1.5×1.5×0.38 mm3) embeddedin kapton substrate with 1 cm pitch, spanning a 10×10 cm2 area in total. A geometrically identical,water equivalent volume was simulated concurrently for comparison. The dose response of the silicondiode array was assessed for various photon beam field shapes and sizes, including an IMRT field, at1 T. The dose response was further investigated at larger magnetic field strengths (1.5 and 3 T) for a4×4 cm2 photon field size.Results: The magic plate diode array shows excellent correspondence (<±1%) to water dose in thein-line orientation, for all beam arrangements and magnetic field strengths investigated. The perpendicularorientation, however, exhibits a dose shift with respect to water at the high-dose-gradientbeam edge of jaw-defined fields [maximum (4.3 ±0.8)% over-response, maximum (1.8 ±0.8)%under-response on opposing side for 1 T, uncertainty 1?]. The trend is not evident in areas within-field dose gradients typical of IMRT dose maps.Conclusions: A novel 121 pixel silicon diode array detector has been characterized by MonteCarlo simulation for its performance inside magnetic fields representative of current prototype andproposed MRIlinear accelerator systems. In the in-line orientation, the silicon dose is directlyproportional to the water dose. In the perpendicular orientation, there is a shift in dose responserelative to water in the highest dose gradient regions, at the edge of jaw-defined and single-segmentMLC fields. The trend was not observed in-field for an IMRT beam. The array is expected to bea valuable tool in MRIgRT dosimetry. ©2015 American Association of Physicists in Medicine. Source

Butson M.J.,City University of Hong Kong | Butson M.J.,Illawarra Cancer Care Center | Butson M.J.,University of Wollongong | Yu P.K.N.,City University of Hong Kong | And 2 more authors.
Radiation Measurements | Year: 2010

Gafchromic EBT2, Radiochromic film is assessed for its change in optical density response to x-ray radiation over a broad energy range, from low energy kilovoltage to megavoltage x-rays. A small energy dependence was found with variations in the change in optical density when scanned in the red component of a desktop scanner light source per unit dose of 6.5% from 50 kVp to 10 MV. This produces a slightly smaller and thus even more energy independent film than its predecessor, EBT film whose response varied by 7.7% over the same energy range. The energy response peaked at 100 kVp with a 5% over response compared to 6 MV x-rays and the minimum response found at both 50 kVp and 250 kVp being a 1.5% under response. It should be noted that the shape of the energy dependence response curve increases from 50 kVp up to 100 kVp followed by a decrease through to higher energies whilst the original EBT was found to increase in response from 50 kVp through to 10 MV. A reflected net optical density change of 0.215 ± 0.006 OD for the first Gray of radiation was found for EBT2 analysed in reflection mode at 6 MV x-ray energy. The minimal energy dependence of the EBT2 film provides further enhancement compared to EBT for its accuracy with respect to spectral changes in the beam to measure beams such as IMRT where complex field and multileaf collimator configurations exist causing small spectral changes to occur over the treatment field or at depth where spectral changes also occur. © 2010 Elsevier Ltd. All rights reserved. Source

Huang C.-Y.,University of New South Wales | Oborn B.M.,Illawarra Cancer Care Center | Oborn B.M.,University of Wollongong | Guatelli S.,University of Wollongong | Allen B.J.,University of New South Wales
Medical Physics | Year: 2012

Purpose: Metastatic melanoma lesions experienced marked regression after systemic targeted alpha therapy in a phase 1 clinical trial. This unexpected response was ascribed to tumor antivascular alpha therapy (TAVAT), in which effective tumor regression is achieved by killing endothelial cells (ECs) in tumor capillaries and, thus, depriving cancer cells of nutrition and oxygen. The purpose of this paper is to quantitatively analyze the therapeutic efficacy and safety of TAVAT by building up the testing Monte Carlo microdosimetric models. Methods: Geant4 was adapted to simulate the spatial nonuniform distribution of the alpha emitter 213Bi. The intraluminal model was designed to simulate the background dose to normal tissue capillary ECs from the nontargeted activity in the blood. The perivascular model calculates the EC dose from the activity bound to the perivascular cancer cells. The key parameters are the probability of an alpha particle traversing an EC nucleus, the energy deposition, the lineal energy transfer, and the specific energy. These results were then applied to interpret the clinical trial. Cell survival rate and therapeutic gain were determined. Results: The specific energy for an alpha particle hitting an EC nucleus in the intraluminal and perivascular models is 0.35 and 0.37 Gy, respectively. As the average probability of traversal in these models is 2.7% and 1.1%, the mean specific energy per decay drops to 1.0 cGy and 0.4 cGy, which demonstrates that the source distribution has a significant impact on the dose. Using the melanoma clinical trial activity of 25 mCi, the dose to tumor EC nucleus is found to be 3.2 Gy and to a normal capillary EC nucleus to be 1.8 cGy. These data give a maximum therapeutic gain of about 180 and validate the TAVAT concept. Conclusions: TAVAT can deliver a cytotoxic dose to tumor capillaries without being toxic to normal tissue capillaries. © 2012 American Association of Physicists in Medicine. Source

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