Inclusion Criteria:  Patient with histologically confirmed endometrial adenocarcinoma, serous or clear cell carcinoma.  Patient is a candidate for adjuvant pelvic radiation for uterine cancer (+/- vault brachytherapy), meeting one of the following conditions:  High grade histology (including serous and clear cell) OR Outer-half myometrial invasion and International Federation of Gynecology and Obstetrics (FIGO) grade 1-2 OR FIGO stage II - III.  Patients who are to receive adjuvant systemic therapy sequentially in addition to pelvic radiotherapy will be eligible. Age ≥18 years. Patient is willing and able to give informed consent to participate in this clinical trial.  Exclusion Criteria:  Patient has had prior pelvic radiotherapy. Patient has a contraindication to pelvic radiotherapy, such as but not limited to a connective tissue disease or inflammatory bowel disease. Patient planned for concurrent chemoradiation therapy.