For a glioblastoma patient who had an MRI immediately postoperatively and you are able to repeat one closer to the time of CT simulation, do you use the more recent scan or the immediate postoperative scan for contouring (T2/FLAIR and T1 post)?

We usually obtain a repeat MRI closer to the time of CT sim, ideally on the day of sim, for several reasons. First, surgical cavities have a tendency to collapse which may impact target volume delineation. Secondly, peritumoral edema T2FLAIR signal infrequently subsides, which may also affect target...