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Australasian Physical & Engineering Sciences in Medicine: The Official Journal of the Australasian College of Physical Scientists and Engineers in Medicine (v.34, #1)
DART, a platform for the creation and registration of cone beam digital tomosynthesis datasets by Vikren Sarkar; Chengyu Shi; Niko Papanikolaou (pp. 5-13).
Digital tomosynthesis is an imaging modality that allows for tomographic reconstructions using only a fraction of the images needed for CT reconstruction. Since it offers the advantages of tomographic images with a smaller imaging dose delivered to the patient, the technique offers much promise for use in patient positioning prior to radiation delivery. This paper describes a software environment developed to help in the creation of digital tomosynthesis image sets from digital portal images using three different reconstruction algorithms. The software then allows for use of the tomograms for patient positioning or for dose recalculation if shifts are not applied, possibly as part of an adaptive radiotherapy regimen.
Keywords: Tomosynthesis; Toolkit; Data creation; Registration
An automatic method of the isocentre position verification for micromultileaf collimator based radiosurgery system by Jacek Chojnowski; Romuald Gajewski (pp. 15-21).
An efficient procedure has been developed using an electronic portal imaging device (EPID) and in-house written software for verification of a target simulator alignment with the radiation isocentre. A 5 mm tungsten ball is aligned to a linac isocentre based on a lasers intersection point. The BrainLab® m3™ add-on multileaf collimator (MLC) forms a rectangular open field of 1.8 × 1.8 cm2. At five different gantry and couch positions, EPID images are acquired. A computer search algorithm determines the centres of both a radiation field and a tungsten ball for each image. Based on the geometric differences between those centres, the optimum three-dimensional shift of a tungsten ball is calculated in order to minimise the misalignment error between a target simulator and a radiation isocentre. A decision can then be made whether or not the tungsten ball and lasers intersection point should be corrected. The accuracy and precision of the procedure has been tested and found to be 0.04 and 0.24 mm respectively at 95% confidence interval. The procedure is also quicker, easier and more reliable to perform compared to the previous method based on irradiating a radiographic film.
Keywords: Target positioning; Stereotactic radiosurgery; Electronic portal imaging
Method for selection of femoral component in total knee arthroplasty (tka) by Dawie van den Heever; Cornie Scheffer; Pieter Erasmus; Edwin Dillon (pp. 23-30).
A method is proposed enabling a surgeon to preoperatively determine the preeminent type and size of prosthesis, from those available, to be used in a particular patient undergoing knee replacement surgery. Parameters of healthy knee geometry were estimated by employing an unsupervised neural network. These estimated parameters were then applied in a χ2 goodness of fit (GoF) test to determine which femoral prosthesis type and size delivers the most appropriate fit. This approach was used to determine the most suitable match of three implants for 34 different cases. Implant C performed the best and was the optimal fit in 59% of the cases, Implant A was the best fit in 38% of the cases and Implant B the best fit in 3% of the cases. This method shows promise in aiding a surgeon to select the optimal prosthesis type and size from an array of different conventional total knee replacements.
Keywords: Femoral component; Goodness of fit; Method of selection; Prosthesis type; Total knee arthroplasty
A percolation-like model for simulating inter-cellular diffusion in the context of bystander signalling in tumour by C. R. Moulton; A. J. Fleming; M. A. Ebert (pp. 31-39).
Despite ongoing active research, the role of the radiation bystander effect in modifying local tissue response to an ionising radiation dose remains unclear. The present study aims to provide new insight by simulating the diffusion-mediated inter-cellular communication processes in 2D and 3D cell-like structures to calculate likely signal ranges in the diffusion limited case. Random walks of individual signalling molecules were tracked between cells with inclusion of molecule-receptor interactions. The resulting diffusion anomaly is a function of cell density, signal uptake probability and the spatial arrangement of cells local to the signal origin. Uptake probability effects dominate percolation effects in disordered media. Diffusion through 2D structures is more conducive to anomalous diffusion than diffusion through 3D structures. Values for time-dependent diffusion constants and permeability are derived for typical simulation parameters. Even at low signal uptake probabilities the communication range is restricted to a mean value of less than 100 μm owing to complete signal uptake by 600 s. This should be considered in light of the potential influence of signal relaying, flow-dynamics or vasculature-mediated signalling.
Keywords: Diffusion modelling; Bystander effect; Percolation theory; Monte Carlo simulations
Using fuzzy association rule mining in cancer classification by Hamid Mahmoodian; M. Hamiruce Marhaban; Raha Abdulrahim; Rozita Rosli; Iqbal Saripan (pp. 41-54).
The classification of the cancer tumors based on gene expression profiles has been extensively studied in numbers of studies. A wide variety of cancer datasets have been implemented by the various methods of gene selection and classification to identify the behavior of the genes in tumors and find the relationships between them and outcome of diseases. Interpretability of the model, which is developed by fuzzy rules and linguistic variables in this study, has been rarely considered. In addition, creating a fuzzy classifier with high performance in classification that uses a subset of significant genes which have been selected by different types of gene selection methods is another goal of this study. A new algorithm has been developed to identify the fuzzy rules and significant genes based on fuzzy association rule mining. At first, different subset of genes which have been selected by different methods, were used to generate primary fuzzy classifiers separately and then proposed algorithm was implemented to mix the genes which have been associated in the primary classifiers and generate a new classifier. The results show that fuzzy classifier can classify the tumors with high performance while presenting the relationships between the genes by linguistic variables.
Keywords: Fuzzy classifier; Breast cancer; Gene selection; Gene expression profile
Plan evaluation and dosimetric comparison of IMRT using AAPM TG119 test suites and recommendations by Sathiyan Saminathan; Ravikumar Manickam; Varatharaj Chandraraj (pp. 55-61).
In order to verify intensity modulated radiotherapy quality assurance procedure and to establish the practical base line commissioning, American Association of Physicists in Medicine-Task Group 119 test suite DICOM-RT images and structure were downloaded for planning and dosimetric comparison. The square slab phantom of water equivalent plastic was used for the measurement. This phantom can permit point dose measurement with ionization chamber by placing the chamber at 7.5 cm depth in the slab phantom. The planar dose measurements were carried out by positioning the Matrixx detector at 10 cm depth. The planning and measurements were performed as per AAPM TG119 guidelines. The test suite includes AP:PA field, band test, multitarget, prostate, head and neck and C-shape. The ion chamber measurements were within 3% of the planned dose for target and avoidance structure region. The ion chamber measurement results are in good agreement with the TG119 recommendation of ±3% for all the test suites. The planar dose measurements were performed with Matrixx for individual fields at the planned gantry angle. The results show that the pass criteria for γ ≤ 1 were between 93 to 97% for all the test cases. Our results are in good agreement with the TG119 recommendation. The present study aimed to compare the measured dose with the planned dose using computer planning system. The test suites were used to assess the planning and delivery systems so as to provide the basis for IMRT commissioning and QA.
Keywords: IMRT; Commissioning; Quality assurance; Ion chamber; Matrixx
Validation of co-registration of clinical lung ventilation and perfusion SPECT by Steven Marsh; Leighton Barnden; Darin O’Keeffe (pp. 63-68).
Ventilation (V) and perfusion (Q) image data from 20 patients undergoing a routine clinical SPECT V/Q study were aligned via rigid coregistration using intrinsic image intensity values with the software package ‘Qonsub’. Accuracy of the coregistration was quantified by an independent technique that used Tc-99m filled fiducial markers which had been adhered to the patient’s skin prior to imaging. These were visible on both the V and Q scans, but were removed from the images for the coregistration step. The level of inter-marker displacement between scans was monitored to ensure it did not invalidate the assessment of coregistration accuracy. Once coregistered, results showed that for 65% of patients in the survey co-registration accuracy was better than 1 pixel (3.8 mm), 30% were co-registered with an accuracy of between 1 and 2 pixels and 5% were co-registered with an accuracy of between 2 and 3 pixels.
Keywords: SPECT V/Q; Coregistration accuracy analysis; Fiducial markers
On the use of published radiobiological parameters and the evaluation of NTCP models regarding lung pneumonitis in clinical breast radiotherapy by Patricia Svolos; Ioannis Tsougos; Georgios Kyrgias; Constantine Kappas; Kiki Theodorou (pp. 69-81).
In this study we sought to evaluate and accent the importance of radiobiological parameter selection and implementation to the normal tissue complication probability (NTCP) models. The relative seriality (RS) and the Lyman–Kutcher–Burman (LKB) models were studied. For each model, a minimum and maximum set of radiobiological parameter sets was selected from the overall published sets applied in literature and a theoretical mean parameter set was computed. In order to investigate the potential model weaknesses in NTCP estimation and to point out the correct use of model parameters, these sets were used as input to the RS and the LKB model, estimating radiation induced complications for a group of 36 breast cancer patients treated with radiotherapy. The clinical endpoint examined was Radiation Pneumonitis. Each model was represented by a certain dose–response range when the selected parameter sets were applied. Comparing the models with their ranges, a large area of coincidence was revealed. If the parameter uncertainties (standard deviation) are included in the models, their area of coincidence might be enlarged, constraining even greater their predictive ability. The selection of the proper radiobiological parameter set for a given clinical endpoint is crucial. Published parameter values are not definite but should be accompanied by uncertainties, and one should be very careful when applying them to the NTCP models. Correct selection and proper implementation of published parameters provides a quite accurate fit of the NTCP models to the considered endpoint.
Keywords: Radiobiological modeling; Radiotherapy; Radiation pneumonitis; NTCP
Validation and automation of the DYNJAWS component module of the BEAMnrc Monte Carlo code by M. B. Kakakhel; E. S. Baveas; A. L. Fielding; T. Kairn; J. Kenny; J. V. Trapp (pp. 83-90).
The purpose of this work is to validate and automate the use of DYNJAWS; a new component module (CM) in the BEAMnrc Monte Carlo (MC) user code. The DYNJAWS CM simulates dynamic wedges and can be used in three modes; dynamic, step-and-shoot and static. The step-and-shoot and dynamic modes require an additional input file defining the positions of the jaw that constitutes the dynamic wedge, at regular intervals during its motion. A method for automating the generation of the input file is presented which will allow for the more efficient use of the DYNJAWS CM. Wedged profiles have been measured and simulated for 6 and 10 MV photons at three field sizes (5 cm × 5 cm, 10 cm × 10 cm and 20 cm × 20 cm), four wedge angles (15°, 30°, 45° and 60°), at d max and at 10 cm depth. Results of this study show agreement between the measured and the MC profiles to within 3% of absolute dose or 3 mm distance to agreement for all wedge angles at both energies and depths. The gamma analysis suggests that dynamic mode is more accurate than the step-and-shoot mode. The DYNJAWS CM is an important addition to the BEAMnrc code and will enable the MC verification of patient treatments involving dynamic wedges.
Keywords: Enhanced dynamic wedges (EDWs); Monte Carlo; DYNJAWS; Automation; BEAMnrc