Hi Brad,
the waiting game post-radiation is certainly tricky and frustrating. 2 mm is typically considered within the margin of error of the MRI scan. Additionally, swelling is not uncommon for up to 2 years post treatment, and could account for the symptoms that you described. Darkening is a good sign, but by itself is not a definitive indicator of treatment success. My AN did show darkening at 6 and 12 months post-GK, but unfortunately continued to grow.
Radiologists will typically compare scans to the previous ones, and may interpret slight changes in different ways. It is important to have the same person interpreting your MRI each time. Also, watch not so much the variations between subsequent scans, but for the long term trend. If the changes are within the margin of error, there should be some fluctuation. If there is consistent growth in the long term, then you must be ready to seek alternative treatment.
I suppose you are in Manitoba and obviously there aren't many specialists around. There are quite a few specialists in Canada, so if needed you do have options.
Good luck and I do hope that your treatment works.
Marianna