Doses of total body irradiation used in bone marrow transplantation typically range from 10 to >12 Gy. For reference, a dose of 4.5 Gy is fatal in 50% of exposed individuals without aggressive medical care. At these doses, total body irradiation both destroys the host's bone marrow (allowing donor marrow to engraft) and kills residual cancer cells. Non-myeloablative bone marrow transplantation uses lower doses of total body irradiation, typically about 2 Gy, which do not destroy the host bone marrow but do suppress the host immune system sufficiently to promote donor engraftment.
In modern practice, total body irradiation is typically fractionated. That is, the radiation is delivered in multiple small doses rather than one large dose. Early research in bone marrow transplantation by E. Donnall Thomas and colleagues demonstrated that this process of splitting TBI into multiple smaller doses resulted in lower toxicity and better outcomes than delivering a single, large dose.
In addition to its use in bone marrow transplantation, total body irradiation has been explored as a treatment modality for high-risk Ewing sarcoma. However, subsequent findings suggest that TBI in this setting causes toxicity without improving disease control, and TBI is not currently used in the treatment of Ewing sarcoma outside of clinical trials.
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