Congratulations, clarmst!
I have read in reports that some AN patients have had their tumor swell over three years after CK, although that's highly unusual.
It is pretty clear to me that the "growth" your doctor reported was simply swelling due to the radiation. The dramatic shrinkage occurred after the swelling phase ended, when your body began to eliminate the dead tissue. At least, this is a much more plausible explanation than failed CK followed by spontaneous and dramatic shrinkage for no apparent reason.
My case is similar to yours, although the timelines are different. My tumor swelled 33% in volume in the first five months following CK and then shrank 59% in the following six months.
I am curious what the measurements of your AN were just prior to treatment. Is it smaller now than it was right before you received CK?
Anyway, whatever the reason is for your good fortune, we all celebrate with you this wonderful outcome. Best wishes for continued good health.
TW