Adjuvant Hypofractionated Whole Pelvis Radiation Therapy in Endometrial Cancer

Inclusion Criteria: * Patients with histologically confirmed stage I, II, or III endometrial cancer who require pelvic radiation as determined by their treating radiation oncologist and/or gynecologic oncologist. Patients may also be identified through the Gynecologic Oncology Multidisciplinary Tumor Board. The decision to include Stage I patients will be based on risk factors for recurrence including tumor grade, extent of myometrial invasion, presence of lymphovascular space invasion, and histology (endometrioid, papillary serous, clear cell, carcinosarcoma). Stage I patients may include those who are ineligible for vaginal cuff brachytherapy due to patient anatomy or those who are at higher risk for pelvic nodal recurrence and pelvic external beam radiotherapy is preferred over vaginal cuff brachytherapy. * Age ≥18 years. * ECOG performance status ≤2 (Karnofsky ≥60%). * Patients must have undergone total hysterectomy and bilateral salpingo-oophorectomy with or without pelvic and/or para-aortic lymph node dissection/sampling or sentinel lymph node (SLN) dissection. * Patients with a prior or concurrent malignancy whose natural history or treatment does not have the potential to interfere with the safety or efficacy assessment of the investigational regimen are eligible for this trial. * Ability to understand and the willingness to sign a written informed consent document. Exclusion Criteria: * Patients with an Inflammatory Bowel Disease diagnosis, regardless of disease activity. * Patients with current, active disease involving periaortic node(s). This is based on histologically positive para-aortic node(s) removed at time of surgery. * Patients with gross residual disease following surgical resection. Final pathologic margins must be negative (no tumor on ink). This may also be determined clinically by the gynecologic oncologist at time of surgery or post-operative imaging if applicable. Post-operative imaging is not required at time of surgery. * Patients who have ever had pelvic radiotherapy prior to entering the study. * Patients who are receiving any other investigational agents. Patients who have received other investigational agents previously who are no longer receiving these investigational agents may be eligible at the discretion of the PI. * Patients with uncontrolled intercurrent illness. * Patients with psychiatric illness/social situations that would limit compliance with study requirements.