Stage I Uterine Corpus Cancer

This randomized phase III trial studies short course vaginal cuff brachytherapy to see how well it works compared with standard of care vaginal cuff brachytherapy in treating participants with stage I-II endometrial cancer. Short course vaginal cuff brachytherapy, also known as internal radiation therapy, uses (over a shorter period) radioactive material placed directly into or near a tumor in the upper portion of the vagina to kill tumor cells. After completion of cohort 1 (108 participants), the protocol was expended to add a second cohort of 80 additional participants, and re-opened study recruitment.