GBM possible recurrence help

Hi all, my brother diagnosed with gbm last year april 2016 and got his surgery, radiation and temodal immediately after that. This year around feb 2017 during his 3months mri checkup the doctor noted a 0.75cm mass suspected as gbm. Bc its too small the doctor decided to wait for next mri to see how it goes. At may 2017 my bro undergo another mri and found out it was clear! But at next mri aug 2017 they found the 'dissapeared' mass to have grown to 1.4cm. The doctor have decided that it must be gbm recurrence, and he said that the missing mass in between these mri must be the gbm 'hiding'. Is it really possible gbm to be 'missed' during mri?

And we also really confused to the best solution in handling this 'possible gbm recurrence'. We have asked diff doctors including neurosurgeons and oncologists. Doctor A said we should go with gamma knife, Doctor B said we should go with Surgery instead cause Gamma knife wont guaranteed as clear as Surgery. Doctor C said Surgery is dangerous cause the mass is in a critical location that can 'paralyzed', and Gamma knife not effective so we should go with Cyberknife instead. Anyone who have experienced gamma or cyber which one is actually more effective for gbm? And for gamma knife do the patient need to undergo chemotherapy after the gamma knife operation like using Avastin? Or they can only wait for the gamma to works? We really appreacite any recommendations or sharing of experience. Thank you!

Regards,
Milee