RecruitingRadiation therapyPartial Stem Cell Transplant for Sickle Cell Disease From Matched DonorsThis is a non-ablative (partial) stem cell transplant for patients with severe sickle cell disease or beta-thalassemia requiring red cell transfusions. The intensity of the transplant is slightly increased from our previous transplant regimens. The goal is to aim for higher percentage of donor cells to stably remain in the recipients long term.