A patch-based pseudo-CT approach for MRI-only radiotherapy in the pelvis
Daniel Andreasen1, Koen Van Leemput2, Jens M Edmund3
1Department of Applied Mathematics and Computer Science, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark and Radiotherapy Research Unit, Department of Oncology, Gentofte and Herlev Hospital, University of Copenhagen, 2730 Herlev, Denmark.
Medical Physics
|August 5, 2016
Summary
This study shows a patch-based method accurately converts MRI scans to pseudo-CT (pCT) for pelvic radiotherapy. This approach, faster than previous methods, improves electron density estimation from MRI data.
Area of Science:
- Medical Physics
- Radiotherapy Technology
- Image Processing
Background:
- Radiotherapy planning requires accurate electron density information, typically from CT scans.
- Magnetic Resonance Imaging (MRI) is increasingly used in radiotherapy, but lacks direct electron density information.
- Converting MRI to pseudo-CT (pCT) is crucial for MRI-only radiotherapy.
Purpose of the Study:
- To evaluate a patch-based method for generating pelvic pseudo-CT (pCT) from T1-weighted MRI scans.
- To assess the accuracy and efficiency of this pCT method compared to a baseline approach.
- To investigate the clinical applicability of the patch-based method in the challenging pelvic region.
Main Methods:
- A patch-based algorithm using T1-weighted MRI and affine registrations was applied to 10 prostate cancer patients.
- Generated pCTs were compared to CT scans using voxel-wise mean absolute error (MAEvox) and path length deviations.
- Dosimetric accuracy was evaluated using dose-volume histogram (DVH) points and gamma index analysis.
Main Results:
- The patch-based method achieved an average MAEvox of 54 HU and a gamma index pass rate of 0.97 (1%/1 mm).
- Median DVH point deviations were below 0.4%, significantly outperforming the baseline water pCT.
- The parallelized approximate patch search reduced pCT generation time by 70x, averaging 20.8 minutes.
Conclusions:
- A T1-weighted MRI-based patch-matching method can accurately generate pCTs for pelvic radiotherapy.
- The primary discrepancies between pCT and CT were attributed to air pockets and anatomical variations.
- The improved speed and accuracy support the clinical utility of this pCT method for MRI-guided radiotherapy.
