|Fig. 1: Gordon Isaacs was the first patient to receive radiation treatment via linear accelerator in 1957. (Source: Wikimedia Commons)|
Total body irradiation is often performed when patients are preparing for a bone marrow transplant. The role of total body irradiation is to to first eliminate the unhealthy bone marrow already existing in the patient's body so that there is room for healthy bone marrow to operate once the transplant is complete.  Total body irradiation is applied to the entire body of the patient, however lead protective aprons are often placed over the patient's lungs so that the risk of radiation induced lung injury is minimized.  Therapy via total body irradiation is carried out when a linear accelerator (see Fig. 1) which sends high energy radiation beams to specific parts of the body.  Total body irradiation is also of the utmost importance in the process of preparing patients for bone marrow transplants because they help to weaken the immune system so that the donor bone marrow can be accepted, thus inhibiting the potentially fatal immunologic rejection of donor tissue.  Thus total body irradiation is especially important in transplant procedures in which the transplanted organs are being transferred between two people who are not related, so that the patient does not experience an autoimmune overreaction to the donor organs. Furthermore, the treatment also helps to eradicate residual cancer cells. Unfortunately, total body irradiation still has its drawbacks as it causes female infertility since only 10 - 14% of women experience full gonadal recovery after receiving treatment. 
Doses of total body irradiation exposure range from about 10 - 12 Gy on average when treatment is required for bone marrow transplant procedures.  More than 2 grays can cause strong reactions (symptoms include symptoms include vomiting and nausea) that demand immediate medical treatment.  This is a significant amount of exposure since one in two people who experience 4.5 Gy of radiation exposure and fail to receive adequate medical treatment does not survive. 
Over time, the practice of applying radiation to different parts of the body instead of applying radiation to the entire body all at once has become commonplace. This procedure is referred to as fractionating. Fractionating saw its popularity rise after research done by Nobel Prize winning physician E. Donnall Thomas showed that fragmenting total body irradiation into smaller doses was a more efficient way to treat patients because of its lower toxicity.  The smaller individual doses sum to a greater amount of total body irradiation than the amount of exposure that is applied when doses are administered simultaneously. Fractionating is useful its staggered treatment allows for the patient's tissue to recover in between sessions - thus preventing excessive harm from occurring to the patient's body while the treatment is still very effective as it allows for existing tissue to be exterminated and donor bone marrow is afforded the room to engraft. permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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