OBJECTIVES: I. To establish the maximum tolerated dose [MTD] of large field image-guided IMRT, using helical tomotherapy when given in combination with intravenous cyclophosphamide and VP-16 as a preparative regimen for allogeneic hematopoietic stem cell transplantation (HSCT) from an human leukocyte antigen (HLA)-identical sibling or unrelated donor in patients with ALL or AML with induction failure or in relapse. (Phase I) II. To describe the toxicity at each dose level standard. (Phase I) III. To collect data on the radiation dose to normal organs and bone marrow using tomotherapy targeted total-body irradiation (TBI). (Phase I) IV. To estimate the overall survival probability, disease free survival probability and relapse rate associated with this regimen. (Phase II) V. To characterize the treatment related mortality and toxicity profile (early/late) associated with this regimen. (Phase II) VI. To descriptively compare the outcomes of patients treated on this protocol to a comparable patient population conditioned with whole body radiation. (Phase II)