Intensity-Modulated Radiation Therapy, Etoposide, and Cyclophosphamide Followed By Donor Stem Cell Transplant in Treating Patients With Relapsed or Refractory Acute Lymphoblastic Leukemia or Acute Myeloid Leukemia

Inclusion Criteria: * Patients with acute lymphocytic leukemia or acute myelogenous leukemia who are not in first or second remission (i.e., after failing remission induction therapy or in relapse or beyond second remission) * All candidates for this study must have a human leukocyte antigen (HLA) (A, B, C, DR) identical sibling who is willing to donate bone marrow or primed blood stem cells or a 10/10 allele matched unrelated donor; a single allele mismatch at A, B, C, DR, or DQ and a KIR mismatch at C will be allowed; all ABO blood group combinations of the donor/recipient are acceptable since even major ABO compatibilities can be dealt with by various techniques * Prior therapy with VP-16, Busulfan, and Cytoxan is allowed * A cardiac evaluation with an electrocardiogram showing no ischemic changes or abnormal rhythm and an ejection fraction of \>= 50% established by multi gated acquisition scan (MUGA) or echocardiogram * Patients must have a serum creatinine of less than or equal to 1.2 or creatinine clearance \> 80 ml/min * A bilirubin of less than or equal to 1.5 * Serum glutamic oxaloacetic transaminase (SGOT) less than 5 times the upper limit of normal * Serum glutamate pyruvate transaminase (SGPT) less than 5 times the upper limit of normal * Pulmonary functioning tests including diffusing capacity of carbon monoxide (DLCO) will be performed; forced expiratory volume in one second (FEV1) and DLCO should be greater than 50% of the predicted normal value * The time fro…