6 months to a Gbm patient could be eternity. Wow!!! where do you live? I can't imagine a doctor doing a follow up MRI every 6 months. I would change doctors ASAP !!! Believe me, I know what I talking about-been there and did those MRI's every 2 months not 6. Any other disease and I would say maybe, but with GBM-no way-sorry just my 2 cents.
Joe