Radiation therapy planning and simulation with magnetic resonance images
2008
We present a system which allows for use of magnetic resonance (MR) images as primary RT workflow modality alone
and no longer limits the user to computed tomography data for radiation therapy (RT) planning, simulation and patient
localization. The single steps for achieving this goal are explained in detail.
For planning two MR data sets, MR1 and MR2 are acquired sequentially. For MR1 a standardized Ultrashort TE (UTE)
sequence is used enhancing bony anatomy. The sequence for MR2 is chosen to get optimal contrast for the target and the
organs at risk for each individual patient. Both images are naturally in registration, neglecting elastic soft tissue
deformations. The planning software first automatically extracts skin and bony anatomy from MR1. The user can semi-automatically
delineate target structures and organs at risk based on MR1 or MR2, associate all segmentations with MR1
and create a plan in the coordinate system of MR1. Projections similar to digitally reconstructed radiographs (DRR)
enhancing bony anatomy are calculated from the MR1 directly and can be used for iso-center definition and setup
verification. Furthermore we present a method for creating a Pseudo-CT data set which assigns electron densities to the
voxels of MR1 based on the skin and bone segmentations. The Pseudo-CT is then used for dose calculation.
Results from first tests under clinical conditions show the feasibility of the completely MR based workflow in RT for
necessary clinical cases. It needs to be investigated in how far geometrical distortions influence accuracy of MR-based
RT planning.
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