This study will investigate if a shorter treatment course (known as "hypofractionation") for pelvic radiation is safe for women with endometrial cancer. Doctors leading the study will also determine the safest and most tolerable dose of shortened radiation (hypofractionation) used to treat women in this study. Because this study will shorten the radiation course typically used to treat endometrial cancer, each daily treatment given to women in this study will be slightly higher than normal to ensure that the total radiation dose they receive is still effective and similar to the radiation dose they would receive if they were not participating in this study (standard treatment).

Inclusion Criteria:

• Diagnosis of primary cervical cancer or uterine cancer of any histology
• Age ≥ 18 years.
• Non-metastatic disease according to the International Federation of Gynecology and Obstetrics (FIGO).
• Must have been treated with definitive intent, including standard-of-care hysterectomy, without any gross residual disease post-operatively. Nodal dissection is not required, but if it is not performed, then diagnostic imaging to confirm absence of gross pelvic or para-aortic disease should be obtained pre- or post-operatively.
• Recommended to undergo whole pelvic radiotherapy without concurrent chemotherapy or para-aortic radiation. Chemotherapy before or after radiotherapy is acceptable.
• Eastern Cooperative Oncology Group (ECOG) PS≤ 2
• Able to provide informed consent and willingness to sign an approved consent form

Exclusion Criteria:

• Distant metastases as determined clinically or radiographically based upon standard-of-care work-up for endometrial cancer.
• Concurrent (or other) chemotherapy occurring at the time of study.
• Gross residual disease (cancer cells that remain after attempts to remove the cancer have been made) post-operatively and/or at the time of radiation based upon pre-op or post-op imaging, intra-operative findings, and gynecologic oncologists' judgment.
• History of small bowel obstruction, inflammatory bowel disease, irritable bowel syndrome, connective tissue disorder requiring ongoing active medical management, or prior radiation therapy directed to the pelvis.
• Unresolved grade 2 or higher chemotherapy-associated diarrhea or abdominopelvic pain requiring medication prior to the initiation of radiation.
• Recommendation to undergo para-aortic nodal irradiation.