The prediction of transmitted dose distributions using a 3D treatment planning system. Australasian physical & engineering sciences in medicine / supported by the Australasian College of Physical Scientists in Medicine and the Australasian Association of Physical Sciences in Medicine. [Australas Phys Eng Sci Med] Journal article

Title	The prediction of transmitted dose distributions using a 3D treatment planning system.
Author(s)	Reich P, Bezak E, Mohammadi M, Fog L
Institution	School of Chemistry and Physics, University of Adelaide, Australia. preich@mail.rah.sa.gov.au
Source	Australas Phys Eng Sci Med 2006 Mar; 29(1):18-29.
MeSH	Algorithms Body Burden Computer Simulation Humans Imaging, Three-Dimensional Models, Biological Neoplasms Phantoms, Imaging Radiographic Image Interpretation, Computer-Assisted Radiometry Radiotherapy Dosage Radiotherapy Planning, Computer-Assisted Radiotherapy, Conformal Relative Biological Effectiveness Reproducibility of Results Research Support, Non-U.S. Gov't Scattering, Radiation Sensitivity and Specificity Subtraction Technique
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.
Language	eng
Pub Type(s)	Evaluation Studies Journal Article
PubMed ID	16623218

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