Hi,
I was preparing an answer for this thread and I just realized that you have done your search already.
So yes, I want to reiterate that I have checked and double checked what is the relevant measurement for radiation. I have also asked the Drs at the Cyberknife forum. The general consensus is that the portion that is located in the CPA is relevant when judging the cutoff for radiation. BUT the shape can also be important - the less spherical it is, the more difficult it is to map treatment. So only a qualified radiation oncologist can judge each individual case. Also, it is my personal observation from reading posts on this forum that neurosurgeons will tend to report the largest size (including the portion inside the IAC), whereas radiation oncologists may report only the portion in the CPA. This can be the cause of big discrepancies in the reported size and a lot of confusion.
I can see Tumbleweed's point about your husbands' measurements: An "additional" 1.3 cm seems a bit too much. For example my AN (which I consider "large", is 2.9 cm in the transverse direction with "only" an additional 0.5 cm in the IAC.). So I wonder how exactly the radiologists measures the additional 1.3 cm. As mentioned before, the only way to figure this out is to talk to a qualified specialist. And I will agree with TW, the sooner the better, given the uncertainty about the size.
All the best,
Marianna