Total body irradiation-based conditioning in allogeneic transplantation in patients with hematological malignancies: impact in outcomes by stem-cell source.

PURPOSE: Total body irradiation is widely used in conditioning regimens before allogeneic hematopoietic stem-cell transplantation (allo-HSCT), most often in high-risk acute lymphoblastic leukemia. This study assessed survival outcomes and treatment-related toxicity in patients who underwent TBI-based myeloablative conditioning. METHODS: We conducted a retrospective single-center study of patients who underwent allo-HSCT after TBI-based conditioning at a reference TBI-unit serving transplant across the Community of Madrid. Between 2011 and 2020, most patients (n = 52) received 10 Gy in 2 Gy fractions twice daily. Primary endpoints were overall survival (OS), disease-free survival (DFS), and relapse; secondary endpoints included non-relapse mortality (NRM), disease-related mortality (DRM), and toxicity. RESULTS: 58 patients underwent TBI-based conditioning using peripheral blood stem cells (PBSC; n = 37), umbilical cord blood (UCB; n = 19), or bone marrow (BM; n = 1); one patient died before graft infusion. Diagnoses were B-ALL (79.3%), followed by T-ALL (15.5%), non-Hodgkin lymphoma (3.4%), and acute myeloid leukemia (1.7%). Median follow-up was 28 months. At 12 months, OS, DFS, and relapse were 64%, 48%, and 29%, respectively. PBSC transplantation had significantly higher 12-month OS than UCB (78% vs. 37%, p < 0.001). Six-month NRM was 5% and 8% in PBSC recipients vs. 43% and 54% in UCB (p < 0.001). Graft-versus-host disease occurred in 51.7%, pulmonary complications in 32.8%, and neurological toxicity in 25.9%. Secondary malignancies were reported in four patients. CONCLUSION: TBI-based conditioning achieved acceptable outcomes in PBSC recipients but was associated with markedly higher NRM in UCB recipients. These findings highlight graft source as a critical determinant of survival and support individualized strategies in allo-HSCT.