For anal cancer, daily CBCT for the first three fractions to evaluate bladder filling mostly (and to make sure there's not surprise excessive gas in the anus/rectum). After that, KV daily and CBCT weekly. If treating with a vaginal dilator in, I may CBCT more frequently to evaluate its position.

I use daily kv imaging, including for prone IMRT, which is how I most often treat anal cancer. I have not found that cone beam CT scans lead to changes in set up, but this is a controversial area and I am very open to hearing from others who find weekly or even daily CBCT scans helpful.

Agree that the above approaches are reasonable and @Harvey J. Mamon's comment that this is a controversial area. Nevertheless, IGRT parameters should be individualized. There are pitfalls in using across-the-board departmental IGRT policies based on organ site. A rectal cancer patient getting 3-fie...