Program Information
Real-Time Pseudo-CT Creation From Orthogonal Two Dimensional Cinematic MRI for Tumor Tracking
M Mueller1*, C Paganelli2 , D Lee3 , P Keall4 , (1) German Cancer Research Center, Heidelberg, Germany, (2) Politecnico di Milano, Milan, Italy, (3) Virginia Commonwealth University, Richmond, VA, (4) University of Sydney, Camperdown,
Presentations
TH-AB-205-6 (Thursday, August 3, 2017) 7:30 AM - 9:30 AM Room: 205
Purpose: An important aim of modern MRI guided radiotherapy is real-time tumor tracking for lung. However, MRI guided radiotherapy faces is limited by high acquisition time for common MRI sequences and lack of electron density information. To overcome these problems, we proposed a method to achieve pseudo-CT estimation with motion field reshaping.
Methods: The proposed method uses fast-acquired 2D cine-MRIs to estimate corresponding 3D pseudo-CT for real-time adaptation. The first pre-treatment step was to create an electron density map that equaled the morphology described by an inhale MRI volume firstly, with multi-modal deformable image registration (DIR). Secondly, via mono-modal DIR from breath hold inhale to exhale MRI a 3D motion field was derived, which described the reference breathing motion.For real-time motion estimation, 467 sets of cinematic MRI (acquisition time: 250msec/slice) from one patient were used as real-time information, which could also be acquired during treatment on an MRI-linac. Principal Component Analysis was used to analyze the cine-MRI to rescale the reference 3D motion field to deform the inhale electron density map and achieve a real-time pseudo-CT. Chest surface and tumor contour were used to indicate unusual movement not caused by reference motion.
Results: For all tested cine-MRI sets, a 3D pseudo-CT was created successfully. Qualitative as well as quantitative validation showed that the diaphragm position alone delivered capable results to describe the 3D breathing motion when used for rescaling the reference motion field in regular cases. The difference in diaphragm position between estimated pseudo-CT and cine-MRI was less than 4.2mm for a total movement of 40±1.48mm, including registration uncertainties.
Conclusion: The feasibility and benefits of the developed method for real-time pseudo-CT creation from 2D cinematic MRI were demonstrated for the first time on the basis of breathing motion. Its clinical implementation can enable adaptive lung cancer treatment for MRI-linac machines.
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