This phase I trial studies the side effects and the best dose of intensity modulated total marrow irradiation (IMTMI) when given together with fludarabine phosphate and melphalan in treating patients with cancers of the blood (hematologic) that have returned after a period of improvement (relapsed) undergoing a second donor stem cell transplant. IMTMI is a type of radiation therapy to the bone marrow that may be less toxic and may also reduce the chances of cancer to return. Giving fludarabine phosphate, melphalan, and IMTMI before a donor stem cell transplant may help stop the growth of cells in the bone marrow, including normal blood-forming cells (stem cells) and cancer cells. It may also stop the patient's immune system from rejecting the donor's stem 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.