Al's Comment:

 This one may apply to most people interested in brain tumors.  MRIs are not as accurate as you think they are. Many times the doctors are not sure if what they see on the scan is new tumor growth or pseudoprogression - which are changes relating to radiation injuries and treatment effects.  This doctor has a way to help tell the difference.  It can also tell earlier if a treatment  is working or not, so you have more time to change to a different treatment. Very important stuff.