Surgery With or Without Postoperative Intensity Modulated Radiation Therapy in Treating Patients With Urothelial Bladder Cancer

Inclusion Criteria (A patient cannot be considered eligible for this study unless ALL of the following conditions are met.): * Initial histological diagnosis of muscle invasive urothelial carcinoma * Patients must have undergone a radical cystectomy (reconstructed urinary diversion may be non-continent diversions (eg, ileal conduits) or continent non-orthotopic catheterizable diversions (eg, Indiana pouch) or continent orthotopic diversions (eg, Studer pouch or neobladder)for urothelial bladder carcinoma within 105 days prior to registration. Final cystectomy pathology must be either pure urothelial carcinoma or dominant urothelial carcinoma with admixture of other histologies excluding small cell variants. * Neoadjuvant (preoperative) or adjuvant (postoperative) chemotherapy for the bladder cancer is permitted; however, all patients, even those who will receive adjuvant chemotherapy, must be registered within 105 days after completing cystectomy regardless of whether adjuvant chemotherapy has started. Patients who will be receiving adjuvant (postoperative) chemotherapy will be randomized within 28 days of completing that chemotherapy. * Patients with the following pTNM stages per the American Joint Committee on Cancer (AJCC) 7th ed. are eligible: * pT3apN0; pN1; pN2 provided less than 10 nodes dissected and/or positive surgical margins * pT3bpN0; pN1; pN2 * pT4apN0; pN1; pN2 * pT4bpN0; pN1; pN2 * Appropriate stage for study entry based on the following diagnostic workup: * History/physical examination =\< 45 days prior to registration; * CT or MRI or positron emission tomography(PET)-CT that includes chest, abdomen and pelvis should be performed for initial radiological staging. This may be performed pre- or post-surgery ≤ 90 days prior to registration except in patients getting postoperative adjuvant chemotherapy, who will require CT, MRI or PET-CT including the chest and abdomen and pelvis no more than 30 days prior to registration. Imaging performed postoperatively should show no evidence of residual disease. * Age \>=18 * Zubrod performance status 0-2 =\< 45 days prior to registration * Complete blood count (CBC)/differential obtained ≤ 14 days prior to registration with adequate bone marrow function defined as follows: * Absolute neutrophil count (ANC) \>= 1,500 cells/mm\^3 * Platelets \>= 100,000 cells/mm\^3 * Hemoglobin \>= 8.0 g/dl (NOTE: the use of transfusion or other intervention to achieve hemoglobin \[Hgb\] \>= 8.0 g/dl is acceptable) * The patient must provide study-specific informed consent prior to study entry * The patient must provide study-specific informed consent prior to study entry. Exclusion Criteria (Patients with any of the following conditions are NOT eligible for this study.): * Definitive clinical or radiologic evidence of metastatic disease; pN3 disease is not allowed (positive common iliac node). * Prior invasive solid tumor or hematological malignancy (except non-melanomatous skin cancer and incidentally discovered prostate cancer at time of cystoprostatectomy) unless disease free for a minimum of 3 years * Prior radiotherapy to the pelvis * Patients with a history of inflammatory bowel disease * Patients who have required any treatment (medical or surgical) for bowel obstruction prior to diagnosis of bladder cancer or who have required surgical treatment for bowel obstruction after the cystectomy * Severe, active co-morbidity defined as follows: * Unstable angina and/or congestive heart failure requiring hospitalization within the last 6 months; * Transmural myocardial infarction within the last 6 months; * Acute bacterial or fungal infection requiring intravenous antibiotics at the time of registration; * Severe hepatic disease, defined as a diagnosis of Child-Pugh Class B or C hepatic disease; * HIV positive with CD4 count \< 200 cells/microliter. Note that patients who are HIV positive are eligible, provided they are under treatment with highly active antiretroviral therapy (HAART) and have a CD4 count ≥ 200 cells/microliter within 30 days prior to registration. Note also that HIV testing is not required for eligibility for this protocol. * Other major medical illness which requires hospitalization or precludes study therapy at the time of registration. * Women who are breastfeeding