In this comparative study, the investigators aim to compare prospective pediatric patients who receive total lymphoid irradiation (TLI) using tomotherapy with age- and disease-matched controls who receive conventional total body irradiation (TBI) as part of conditioning for haploidentical hematopoietic stem cell transplantation (HSCT) for both malignant and non-malignant diseases. The investigators shall evaluate graft failure-free, graft-versus-host disease (GVHD)-free survival, overall survival, frequency of rejection, GVHD, relapse of malignancy, adverse effects and post-transplant immunoreconstitution.