Total Marrow and Lymphoid Irradiation

This phase I studies the side effects and best dose of total marrow and lymphoid irradiation when given together with fludarabine and melphalan before donor stem cell transplant in treating participants with high-risk acute leukemia or myelodysplastic syndrome. Giving chemotherapy, such as fludarabine and melphalan, and total marrow and lymphoid irradiation before a donor stem cell transplant helps stop the growth of cells in the bone marrow, including normal blood-forming cells (stem cells) and cancer cells. When the healthy stem cells from a donor are infused into the patient they may help the patient's bone marrow make stem cells, red blood cells, white blood cells, and platelets.