What dose fractionation would you recommend for large (>5 cm) perianal Bowen's disease (squamous cell CIS)?  

I think that peri-anal lesions such as this (and most invasive anal skin cancers as well) are almost always better managed surgically.  It would be the very rare patient who would not tolerate the surgery but would tolerate an aggressive RT course directed to the anal/perianal lesion.  If ...