I agree that it's a good idea to ask for a copy of the MRI and look for yourself. There is a measurement tool included in the software which is easy to use.
I just had my four year post GK scan. My doctor ordered the scan with and without contrast. He insists on contrast even though I don't have any symptoms or problems. When I arrived at the imaging facility I simply told them I didn't want contrast and they didn't force the issue. The next week when I reviewed the MRI results with my doctor he didn't mention the contrast issue. So I didn't either. Of course, should I have problems in the future I will have no problem having a scan with contrast. But for routine monitoring follow up scans it doesn't seem necessary.
Let me reinforce the good advice by rupert, BradL and many others. Take a look at the MRI yourself. Take measurements yourself. The key thing is to have the same person at the same time make the relative measurements. The best candidate is you. Not that you would discount a radiologist, neurosurgeon or radiosurgeon. If you want an interchangeable measurement method, take at look at
https://www.anausa.org/smf/index.php?topic=23670.msg979775078#msg979775078I used to angonise about the correct measurement points when measuring my tumor. However, more recently I've realised that what's more important than size is symptoms and relative change. So even if you measure vertically and horizontally, the relative measurements will be valid.
BTW, after your diagnostic MRI with contrast, a T2 weighted (not to be confused with a 2T MRI machine, which refers to the magnetic strength of 2 Teslas) will allow you to make measurements. And try to get fine slices. I get 0.5 mm slices. 1 mm is probably OK, but 3 mm slices in only going to give you a rough idea.