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Total body irradiation (TBI) is a form of radiotherapy used primarily as part of the preparative regimen for haematopoietic stem cell (or bone marrow) transplantation. As the name implies, TBI involves irradiation of the entire body, though in modern practice the lung
Lung

The lung is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart....
s are often partially shielded to lower the risk of radiation-induced lung injury. In addition, smaller doses of radiation may be used to treat the lungs, in order to destroy any marrow in the area without inflicting the severe harm that the more intense radiation would likely cause in this sensitive region.






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Total body irradiation (TBI) is a form of radiotherapy used primarily as part of the preparative regimen for haematopoietic stem cell (or bone marrow) transplantation. As the name implies, TBI involves irradiation of the entire body, though in modern practice the lung
Lung

The lung is the essential respiration organ in air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located in the chest on either side of the heart....
s are often partially shielded to lower the risk of radiation-induced lung injury. In addition, smaller doses of radiation may be used to treat the lungs, in order to destroy any marrow in the area without inflicting the severe harm that the more intense radiation would likely cause in this sensitive region. Total body irradiation in the setting of bone marrow transplantation serves to destroy or suppress the recipient's immune system, preventing immunologic rejection
Transplant rejection

Transplant rejection occurs when a Organ transplant organ or tissue is not accepted by the body of the transplant recipient. This is explained by the concept that the immune system of the recipient attacks the transplanted organ or tissue....
 of transplanted donor bone marrow
Bone marrow

Bone marrow is the flexible biological tissue found in the hollow interior of bones. In adults, marrow in large bones produces new blood cells....
 or blood stem cells. Additionally, high doses of total body irradiation can eradicate residual cancer
Cancer

Cancer is a class of diseases in which a group of cell display uncontrolled growth , invasion , and sometimes metastasis . These three malignant properties of cancers differentiate them from benign tumors, which are self-limited, do not invade or metastasize....
 cells in the transplant recipient, increasing the likelihood that the transplant will be successful.

Doses of total body irradiation used in bone marrow transplantation typically range from 10 to >12 Gy
Gray (unit)

The gray is the SI unit of absorbed dose due to ionizing radiation ....
. 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
E. Donnall Thomas

Dr. Edward Donnall Thomas is an American physician, professor emeritus at the University of Washington, and director emeritus of the clinical research division at the Fred Hutchinson Cancer Research Center....
 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 trial
Clinical trial

In health care, clinical trials are conducted to allow safety and efficacy data to be collected for new drugs or devices. These trials can only take place once satisfactory information has been gathered on the quality of the product and its non-clinical safety, and Institutional review board approval is granted in the country where the trial...
s.