Optimization of MRI pulse sequences and gadobutrol-doped polymer gel for real time 4D radiation dosimetry on the MRI-Linac

Different MRI pulse sequences can be applied to acquire real time dose distributions on an MRI-Linac. The temporal resolution is affected by the MRI pulse sequence type, the MRI pulse sequence parameters and the NMR relaxation-dose response of the polymer gel. To obtain a sufficiently high temporal resolution, it is crucial to optimize the MRI pulse sequence parameters such as TE, TR and flip angle. The optimization goal is to obtain the highest dose resolution within the shortest time frame, i.e. the smallest temporal uncertainty. We here also demonstrate that it is possible to further improve the temporal uncertainty of the polymer gel dosimeter by adding an MRI contrast agent. The optimization of two MRI pulse sequences in combination with a gadobutrol-doped MAGAT polymer gel dosimeter is discussed.