This clinical trial studies how well cesium-131 low-dose rate interstitial brachytherapy works as an organ-preserving radiation technique in the treatment of patients with cervical and endometrial cancer that has come back in the vagina after a period of improvement following pelvic radiation therapy (vaginal recurrence). In cervical and endometrial cancer patients with vaginal recurrence following pelvic radiation therapy, the only curative option involves a major surgical procedure which removes all the contents of the pelvic cavity, such as the uterus, cervix, bladder, rectum, vagina, and vulva. This procedure is complex and comes with many side effects; therefore, a need remains to improve radiation treatment techniques so radiation therapy can be offered as an alternative treatment option for these patients. Cesium-131 low-dose rate interstitial brachytherapy is a form of internal radiation therapy called brachytherapy. It uses grain-of-rice-sized radioactive seeds implanted directly into or near where the tumor has returned. The implanted seeds give off radiation to kill tumor cells for only a short time after they are placed. Most of the radiation is gone within a few weeks. The seeds stay in the body permanently, but they become inactive quickly. Cesium-131 low-dose rate interstitial brachytherapy may be an effective organ-preserving radiation technique for the treatment of cervical and endometrial cancer patients with vaginal recurrence following pelvic radiation therapy

Inclusion Criteria:

• Patients must have histologically or cytologically confirmed vaginal recurrence of endometrial (endometrioid adenocarcinoma, uterine serous, carcinosarcoma, clear cell) or cervical (squamous, adenosquamous, or adenocarcinoma) cancer and prior history of pelvic radiation.
• Patients must have vaginal recurrence that is amenable to cesium implant for salvage
• Patients must have a vaginal lesion that is measurable according to RECIST 1.1 criteria; that is, at least 1 cm upon measurement by CT, or MRI if the patient cannot have a CT with contrast or lesion is not visualized on CT scan, or measurement by calipers if the lesion is not seen on CT or MRI.
• Patients must have previous external beam radiation treatment to the pelvis for the uterine cervix or endometrial malignancy that has recurred to be eligible for this study, so long as the prior exposure does not exceed tolerance at the discretion of the treating physician.
• Gynecologic Oncology Group performance status of 0, 1, or 2 (see Appendix A).
• There are no minimum organ/marrow function requirements because patients will not be receiving systemic therapy.
• Ability to understand and the willingness to sign a written informed consent document.

Exclusion Criteria:

• Patients who have another concurrent, active invasive malignancy or have had a prior invasive malignancy diagnosed within the last three years, with the following two exceptions: [a] non-melanoma skin cancer and/or [b] prior in situ carcinoma of the cervix and/or [c] in situ bladder cancer.
• Patients who have metastatic or regional lymph node metastases who have radiographic evidence of disease at time of study enrollment. Patients who have had metastasis or lymph nodes previously treated without radiographic disease at time of study enrollment may be considered at discretion of the treating radiation oncologist.
• Receipt of epoetin alpha (Procrit, Epogen) within 1 month of study screening.
• History of allergic reactions attributed to compounds of similar chemical or biologic composition to Cesium-131 implant or other agents used in this study.
• Pregnant women are excluded from this study because radiation is a known teratogen. Patient must agree to use two forms of birth control if they are of child-bearing potential. For this reason, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry, throughout duration of active treatment and for two months after completion of radiation. Should a woman become pregnant or suspect she is pregnant while she is participating in this study, she should inform her treating physician immediately.