For a patient with advanced serous fallopian tube carcinoma involving the uterus, cervix, and vagina who is now s/p interval debulking surgery, would you offer adjuvant vaginal brachytherapy if the upper vaginectomy margin was positive?

I would not. For advanced serous ovarian cancer, the risk of peritoneal recurrence is very high. I do not feel that vaginal brachytherapy would meaningfully affect recurrence rate or prognosis. If the patient has future isolated recurrence at the vagina, I might consider systemic therapy + radiation...

It’s a data-free zone, but based on the description, I would consider brachy alone (6 to 7 Gy x 5 prescribed to visible vaginal thickness) between chemotherapy.