Total body irradiation for bone marrow transplantation

Purpose/Objective: The primary goal of this course is to develop an understanding of the rationale for the use of total body irradiation (TBI) as a component of cytoreduction for bone marrow transplantation, the techniques used, and the results of changing important parameters, such as dose, dose rate, and fractionation. Materials and Methods: Basic radiobiological principles relevant to TBI are reviewed; in particular, emphasis is placed on cell and animal studies which suggest means of optimizing TBI delivery to achieve maximum tumor cell kill and immunosuppression along with minimal normal tissue damage. Techniques utilized at various centers are described, with some discussion of achieving homogeneity, as well as inhomogeneity when desired with partial shielding or 'boosting'. A review of clinical studies, both randomized and non-randomized, is done; these are then interpreted in terms of potential optimization of the TBI parameters. Finally, comparison of TBI-containing regimens with chemotherapy-only regimens is done. Results: Radiobiological studies suggest a potential advantage for fractionated TBI over single dose TBI. Clinical studies support this view: highly fractionated regimens have allowed higher total doses to be used to increase malignant cell kill and immunosuppression without increasing toxicity. Randomized studies of TBI combined with VP-16 or cyclophosphamide versus busulfan combined with cyclophosphamide have either shown an advantage with TBI (in acute myelocytic leukemia in first remission) or no difference (in chronic myelogenous leukemia, chronic phase). Conclusion: TBI has been an effective component of cytoreductive regimens for marrow transplantation in patients with malignant disease, especially leukemias, which constitute 73% of all marrow transplants worldwide. Evidence supports fractionated TBI, to doses ≥ 13 Gy, when compared with single dose TBI. Randomized studies support the continued use of TBI in AML, and suggest that busulfan may be able to replace TBI for CML, but long-term results are pending