Total body irradiation

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 lungs are often partially shielded to lower the risk of radiation-induced lung injury. [cite journal |author=Gore EM, Lawton CA, Ash RC, Lipchik RJ |title=Pulmonary function changes in long-term survivors of bone marrow transplantation |journal=Int. J. Radiat. Oncol. Biol. Phys. |volume=36 |issue=1 |pages=67–75 |year=1996 |month=August |pmid=8823260 |doi= |url=http://linkinghub.elsevier.com/retrieve/pii/S036030169600123X] [cite journal |author=Soule BP, Simone NL, Savani BN, "et al" |title=Pulmonary function following total body irradiation (with or without lung shielding) and allogeneic peripheral blood stem cell transplant |journal=Bone Marrow Transplant. |volume=40 |issue=6 |pages=573–8 |year=2007 |month=September |pmid=17637691 |doi=10.1038/sj.bmt.1705771 |url=] Total body irradiation in the setting of bone marrow transplantation serves to destroy or suppress the recipient's immune system, preventing immunologic rejection of transplanted donor bone marrow or blood stem cells. Additionally, high doses of total body irradiation can eradicate residual cancer 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. For reference, a dose of 4.5 Gy is fatal in 50% of exposed individuals without aggressive medical care. [ [http://www1.va.gov/emshg/docs/Radiological_Medical_Countermeasures_Indexed-Final.pdf Department of Homeland Security Working Group on Radiological Dispersal Device (RDD) Preparedness] , from the United States Department of Homeland Security. Accessed May 29 2008.] 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. [cite journal |author=Thomas ED, Buckner CD, Clift RA, "et al" |title=Marrow transplantation for acute nonlymphoblastic leukemia in first remission |journal=N. Engl. J. Med. |volume=301 |issue=11 |pages=597–9 |year=1979 |month=September |pmid=381925 |doi= |url=] [cite journal |author=Thomas ED, Clift RA, Hersman J, "et al" |title=Marrow transplantation for acute nonlymphoblastic leukemic in first remission using fractionated or single-dose irradiation |journal=Int. J. Radiat. Oncol. Biol. Phys. |volume=8 |issue=5 |pages=817–21 |year=1982 |month=May |pmid=7050046 |doi= |url=]

In addition to its use in bone marrow transplantation, total body irradiation has been explored as a treatment modality for high-risk Ewing sarcoma. [cite journal |author=Kinsella TJ, Glaubiger D, Diesseroth A, "et al" |title=Intensive combined modality therapy including low-dose TBI in high-risk Ewing's Sarcoma Patients |journal=Int. J. Radiat. Oncol. Biol. Phys. |volume=9 |issue=12 |pages=1955–60 |year=1983 |month=December |pmid=9463099 |doi= |url=] However, subsequent findings suggest that TBI in this setting causes toxicity without improving disease control, [cite journal |author=Burdach S, Meyer-Bahlburg A, Laws HJ, "et al" |title=High-dose therapy for patients with primary multifocal and early relapsed Ewing's tumors: results of two consecutive regimens assessing the role of total-body irradiation |journal=J. Clin. Oncol. |volume=21 |issue=16 |pages=3072–8 |year=2003 |month=August |pmid=12915596 |doi=10.1200/JCO.2003.12.039 |url=] and TBI is not currently used in the treatment of Ewing sarcoma outside of clinical trials.

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