Radiation therapy plays a large role in many gynecologic cancers. In cervical cancer, it can be used as curative treatment, often in the form of external beam radiation therapy (EBRT), followed by brachytherapy. For endometrial, vulvar, and vaginal cancers, often radiation can be used adjuvantly after surgery, but for patients with unresectable disease, or gross disease left in lymph nodes or elsewhere in the pelvis after surgery, it can also be used with definitive intent. In many of these situations, radiation must be given to relatively high doses in order to eradicate the disease. Although brachytherapy can be used to deliver high doses to the cervix, vagina, vulva, or endometrium, if there is gross nodal disease in the pelvic, para-aortic, or inguinal nodes, EBRT must be used to deliver the high dose of radiation. In the era of 2D or 3D conformal radiation therapy, these doses often exceeded the tolerance of other organs at risk (OAR), especially the small bowel and femoral heads. The advent of intensity-modulated radiation therapy (IMRT) made the delivery of higher doses of radiation feasible, while still respecting normal tissue tolerances. Prior to the use of IMRT, patients with pelvic, para-aortic, or inguinal lymphadenopathy could not be treated adequately with EBRT, and so received only palliative doses of radiation or chemotherapy alone.