A system for developing a radiotherapy treatment plan, the system comprising: a data storage device configured to hold magnetic resonance (MR) image data acquired using a magnetic resonance imaging (MRI) system; at least one processor configured to: receive the MR image data from the data storage device , wherein the MR image data include temporal reshuffled k-space data, and wherein the MR image data comprises 4D MR image data; apply corrections to the 4D MR image data to produce a series of corrected image data ; assemble the series of corrected image data to generate a set of relaxometry maps ; perform a segmentation of a plurality of regions of interest using the set of relaxometry maps ; classify the plurality of regions of interest, using the set of relaxometry maps, to yield a plurality of classified structures ; assign electron density values to the classified structures using an assignment process ; generate, using the electron density values of the classified structures, a set of corrected synthetic electron density images ; and perform a dose calculation using the corrected synthetic electron density images to develop a radiotherapy treatment plan . a data storage device configured to hold magnetic resonance (MR) image data acquired using a magnetic resonance imaging (MRI) system; at least one processor configured to: receive the MR image data from the data storage device , wherein the MR image data include temporal reshuffled k-space data, and wherein the MR image data comprises 4D MR image data; apply corrections to the 4D MR image data to produce a series of corrected image data ; assemble the series of corrected image data to generate a set of relaxometry maps ; perform a segmentation of a plurality of regions of interest using the set of relaxometry maps ; classify the plurality of regions of interest, using the set of relaxometry maps, to yield a plurality of classified structures ; assign electron density values to the classified structures using an assignment process ; generate, using the electron density values of the classified structures, a set of corrected synthetic electron density images ; and perform a dose calculation using the corrected synthetic electron density images to develop a radiotherapy treatment plan . receive the MR image data from the data storage device , wherein the MR image data include temporal reshuffled k-space data, and wherein the MR image data comprises 4D MR image data; apply corrections to the 4D MR image data to produce a series of corrected image data ; assemble the series of corrected image data to generate a set of relaxometry maps ; perform a segmentation of a plurality of regions of interest using the set of relaxometry maps ; classify the plurality of regions of interest, using the set of relaxometry maps, to yield a plurality of classified structures ; assign electron density values to the classified structures using an assignment process ; generate, using the electron density values of the classified structures, a set of corrected synthetic electron density images ; and perform a dose calculation using the corrected synthetic electron density images to develop a radiotherapy treatment plan . <EOS>