Organ-Sparing Marrow-Targeted Irradiation Before Stem Cell Transplant in Treating Patients With High-Risk Hematologic Malignancies

This pilot clinical trial aims to assess feasibility and tolerability of using an LINAC based "organ-sparing marrow-targeted irradiation" to condition patients with high-risk hematological malignancies who are otherwise ineligible to undergo myeloablative Total body irradiation (TBI)-based conditioning prior to allogeneic stem cell transplant. The target patient populations are those with ALL, AML, MDS who are either elderly (\>50 years of age) but healthy, or younger patients with worse medical comorbidities (HCT-Specific Comorbidity Index Score (HCT-CI) \> 4). The goal is to have the patients benefit from potentially more efficacious myeloablative radiation based conditioning approach without the side effects associated with TBI.

PRIMARY OBJECTIVES: I. To assess feasibility and tolerability of OSMI based hematopoietic stem cell transplant (HSCT) as defined by transplant-related mortality (TRM) at day 30 as well as rate of grade II/III organ toxicity (defined by Bearman Regimen-Related Toxicities Scale) attributable to conditioning occurring within 30 days. SECONDARY OBJECTIVES: I. Day 100 transplant-related mortality (TRM). II. Donor chimerism assessment at day 100 (to assess failure of engraftment rate). III. Incidence of acute graft-versus-host disease (aGVHD) by day 100. IV. Incidence of chronic GVHD at one year. V. Cumulative incidence of grade II organ toxicity through day 100. VI. Rate and kinetics of hematopoietic recovery. VII. Incidence of graft failure (primary and secondary). VIII. Rate of infectious complications. IX. Cumulative incidence of relapse, overall survival, and progression-free survival at 1 year. OUTLINE: CONDITIONING REGIMEN: Patients undergo organ-sparing marrow irradiation twice daily (BID) on days -6 to -4 and receive cyclophosphamide intravenously (IV) over 1-2 hours every 24 hours on days -3 to -2. Patients with an unrelated donor also receive anti-thymocyte globulin every 24 hours on days -4 to -2. GVHD PROPHYLAXIS: Patients receive tacrolimus IV or orally (PO) beginning on day -1 and continuing for at least 6 months and methotrexate IV on days 1, 3, 6, and 11. TRANSPLANT: Patients undergo allogeneic peripheral blood progenitor cell or bone marrow transplant on day 0. After completion of study treatment, patients are followed up weekly for 12 weeks, at day 100, and then at 6 and 12 months.