RecruitingRadiation therapyStandard-of-Care Reduced-Intensity Conditioning (RIC) With 200 Versus 400 cGy of Total Body Irradiation (TBI) in Patients With Acute Leukemia Undergoing First Allogeneic Blood or Marrow Transplantation (BMT)This is a randomized phase II trial of standard-of-care reduced-intensity conditioning (RIC) with 200 versus 400 cGy of total body irradiation (TBI) in patients with acute leukemia undergoing first allogeneic blood or marrow Transplantation (BMT). The primary objective is to compare the rates of graft-versus-host disease-free and relapse-free survival (GRFS) between patients in the two cohorts.