With vaginal cuff brachytherapy, do you treat to the surface or a depth and why?

We prescribe to the surface of the vagina but also attend to the dose at depth. For patients receiving only vaginal cuff irradiation we use a prescription of 6 Gy VSD x 5 qod. Although this is a modest dose, it appears to be very effective in preventing vaginal recurrences, even in high-risk cases. ...