An atlas-based electron density mapping method for magnetic resonance imaging (MRI)-alone treatment planning and adaptive MRI-based prostate radiation therapy

Dowling, Jason A., Lambert, Jonathan, Parker, Joel, Salvado, Olivier, Fripp, Jurgen, Capp, Anne, Wratten, Chris, Denham, James W. and Greer, Peter B. (2012) An atlas-based electron density mapping method for magnetic resonance imaging (MRI)-alone treatment planning and adaptive MRI-based prostate radiation therapy. International Journal of Radiation: Oncology - Biology - Physics, 83 1: E5-E11.


Author Dowling, Jason A.
Lambert, Jonathan
Parker, Joel
Salvado, Olivier
Fripp, Jurgen
Capp, Anne
Wratten, Chris
Denham, James W.
Greer, Peter B.
Title An atlas-based electron density mapping method for magnetic resonance imaging (MRI)-alone treatment planning and adaptive MRI-based prostate radiation therapy
Journal name International Journal of Radiation: Oncology - Biology - Physics  (ERA 2012 Listed)    (ERA 2010 Rank A)   Check publisher's open access policy
Publication date 2012-05-01
Sub-type Article
DOI 10.1016/j.ijrobp.2011.11.056
Volume number 83
Issue number 1
ISSN 0360-3016; 1879-355X
Start page E5
End page E11
Total pages 7
Place of publication Philadelphia, PA, United States
Publisher Elsevier
Collection year 2013
Language eng
Formatted abstract Purpose: Prostate radiation therapy dose planning directly on magnetic resonance imaging (MRI) scans would reduce costs and uncertainties due to multimodality image registration. Adaptive planning using a combined MRI-linear accelerator approach will also require dose calculations to be performed using MRI data. The aim of this work was to develop an atlas-based method to map realistic electron densities to MRI scans for dose calculations and digitally reconstructed radiograph (DRR) generation.
Methods and Materials: Whole-pelvis MRI and CT scan data were collected from 39 prostate patients. Scans from 2 patients showed significantly different anatomy from that of the remaining patient population, and these patients were excluded. A whole-pelvis MRI atlas was generated based on the manually delineated MRI scans. In addition, a conjugate electron-density atlas was generated from the coregistered computed tomography (CT)-MRI scans. Pseudo-CT scans for each patient were automatically generated by global and nonrigid registration of the MRI atlas to the patient MRI scan, followed by application of the same transformations to the electron-density atlas. Comparisons were made between organ segmentations by using the Dice similarity coefficient (DSC) and point dose calculations for 26 patients on planning CT and pseudo-CT scans.
Results: The agreement between pseudo-CT and planning CT was quantified by differences in the point dose at isocenter and distance to agreement in corresponding voxels. Dose differences were found to be less than 2%. Chi-squared values indicated that the planning CT and pseudo-CT dose distributions were equivalent. No significant differences (p > 0.9) were found between CT and pseudo-CT Hounsfield units for organs of interest. Mean ± standard deviation DSC scores for the atlas-based segmentation of the pelvic bones were 0.79 ± 0.12, 0.70 ± 0.14 for the prostate, 0.64 ± 0.16 for the bladder, and 0.63 ± 0.16 for the rectum.
Conclusions: The electron-density atlas method provides the ability to automatically define organs and map realistic electron densities to MRI scans for radiotherapy dose planning and DRR generation. This method provides the necessary tools for MRI-alone treatment planning and adaptive MRI-based prostate radiation therapy.
Keyword Electron density
MRI
Prostate cancer
Radiotherapy planning
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status Non-UQ

 
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