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https://hdl.handle.net/2440/49926
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Type: | Journal article |
Title: | The prediction of transmitted dose distributions using a 3D treatment planning system |
Author: | Reich, P. Bezak, E. Mohammadi, M. Fog, L. |
Citation: | Australasian Physical and Engineering Sciences in Medicine, 2006; 29(1):18-29 |
Publisher: | Australasian College of Physical Scientists and Engineers in Medicine |
Issue Date: | 2006 |
ISSN: | 0158-9938 1879-5447 |
Statement of Responsibility: | P. Reich, E. Bezak, M. Mohammadi and L. Fog |
Abstract: | Patient dose verification is becoming increasingly important with the advent of new complex radiotherapy techniques such as conformal radiotherapy (CRT) and intensity-modulated radiotherapy (IMRT). An electronic portal imaging device (EPID) has potential application for in vivo dosimetry. In the current work, an EPID has been modelled using a treatment planning system (TPS) to predict transmitted dose maps. A thin slab of RW3 material used to initially represent the EPID. A homogeneous RW3 phantom and the thin RW3 slab placed at a clinical distance away from the phantom were scanned using a CT simulator. The resulting CT images were transferred via DICOM to the TPS and the density of the CT data corresponding to the thin RW3 slab was changed to 1 g/cm3. Transmitted dose maps (TDMs) in the modelled EPID were calculated by the TPS using the collapsed-cone (C-C) convolution superposition (C/S) algorithm. A 6 MV beam was used in the simulation to deliver 300 MU to the homogenous phantom using an isocentric and SSD (source-to-surface) technique. The phantom thickness was varied and the calculated TDMs in the modelled EPID were compared with corresponding measurements obtained from a calibrated scanning liquid-filled ionisation chamber (SLIC) EPID. The two TDMs were compared using the gamma evaluation technique of Low et al. The predicted and measured TDMs agree to within 2 % (averaged over all phantom thicknesses) on the central beam axis. More than 90 % of points in the dose maps (excluding field edges) produce a gamma index less than or equal to 1, for dose difference (averaged over all phantom thicknesses), and distance-to-agreement criteria of 4 %, 3.8 mm, respectively. In addition, the noise level on the central axis in the predicted dose maps is less than 0.1 %. We found that phantom thickness changes of approximately 1 mm, which correspond to dose changes on the central beam axis of less than 0.6 %, can be detected in the predicted transmitted dose distributions. |
Keywords: | Humans Neoplasms Radiographic Image Interpretation, Computer-Assisted Imaging, Three-Dimensional Subtraction Technique Radiotherapy, Conformal Radiotherapy Dosage Radiotherapy Planning, Computer-Assisted Sensitivity and Specificity Reproducibility of Results Radiometry Body Burden Phantoms, Imaging Relative Biological Effectiveness Algorithms Scattering, Radiation Models, Biological Computer Simulation |
DOI: | 10.1007/BF03178824 |
Published version: | http://dx.doi.org/10.1007/bf03178824 |
Appears in Collections: | Aurora harvest Chemistry and Physics publications |
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