Intensity-Modulated Radiation Therapy to the Pelvis With or Without Chemotherapy in Treating Patients With Endometrial Cancer or Cervical Cancer That Has Been Removed By Surgery

DISEASE CHARACTERISTICS: * Must have undergone a hysterectomy (total abdominal, vaginal, radical, or laparoscopic-assisted vaginal) within 7 weeks prior to study entry * Patients with endometrial cancer must have also undergone a bilateral salpingo-oophorectomy * Histologically confirmed diagnosis of 1 of the following: * Endometrial cancer meeting 1 of the following criteria: * Stage IB grade 3, IC grade 1-3, IIA, or IIB disease requiring postoperative pelvic radiotherapy * Unstaged (no lymph node dissection or sampling) stage IB grade 2 disease * Stage IIIC with all of the following: * Pelvic lymph node positive only * Para-aortic nodes sampled negative * Not receiving chemotherapy * Cervical cancer meeting 1 of the following criteria: * Post-radical hysterectomy and requires postoperative pelvic radiotherapy due to any of the following: * Positive pelvic nodes (negative para-aortic nodes) * Microscopic parametrial involvement and negative margins * Disease qualified by Sedlis criteria must have 2 of the following risk factors: * 1/3 or more stromal invasion * Lymph-vascular space invasion * Large clinical tumor diameter (≥ 4 cm) * Post-simple hysterectomy with negative margins and negative nodes by CT scan, MRI, or positron emission tomography-CT scan * No requirement for extended-field radiotherapy beyond the pelvis * No histologically confirmed papillary serous, clear cell, or n…