Is radiation therapy a treatment option for refractory Paget's disease of the vulva extending onto skin of buttocks and anal margin?
I have treated localized peri-anal Paget's Disease with good outcomes, and there is some data to support this. I have not treated a patient with such widespread vulvar Paget's and I suspect that the morbidity would be significant given the doses required, and the volume to be treated in the case you describe. I think the better approach is probably to use surgery, including repeated surgeries, rather than RT, in more of a "management of chronic disease" kind of philosophy. However, I could see using focal RT in a few selected cases with multiple recurrent focal diseases, but not in the case described.
I would use topical imiquimod cream, an effective and underused modality. It can be used either as curative, or as an adjuvant to radiation. It can either eliminate the need for radiation or greatly decrease the size of the field you will need.
It can cause a skin reaction that looks similar to a radiation reaction, and should be managed the same way. If the reaction is too severe, just put them on a break, until it can be resumed. Healthy skin has a little reaction, preclinical or microscopic involvement will react, so it exposes the area of preclinical involvement.
It has an advantage over radiation in that, an extensive area can be treated piecemeal if necessary, i.e. one part at a time to improve patient tolerance, with no worries about overlap.
If any disease remains after imiquimod, a small radiation field can be used.