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 Radiation-induced lung injury (RILI) is a general term for damage to the lungs as a result of exposure to ionizing radiation. In general terms, such damage is divided into early inflammatory damage (''radiation pneumonitis'') and later complicatio ...

. 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 Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

cells in the transplant recipient, increasing the likelihood that the transplant will be successful.

Dosage

Doses of total body irradiation used in bone marrow transplantation typically range from 10 to >12 Gy. For reference, an unfractionated (i.e. single exposure) dose of 4.5 Gy is fatal in 50% of exposed individuals without aggressive medical care. The 10-12 Gy is typically delivered across multiple fractions to minimise toxicities to the patient. In modern practice, total body irradiation is typically

fractionated Fractionation is a separation process in which a certain quantity of a mixture (of gases, solids, liquids, enzymes, or isotopes, or a suspension) is divided during a phase transition, into a number of smaller quantities ( fractions) in which t ...

, with smaller doses delivered in several sessions, rather than delivering the entire dose at once. 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. The time interval between fractions allows other normal tissues some time to repair some of the damage caused. However, the dosing is still high enough that the ultimate result is the destruction of both the patient's bone marrow (allowing donor marrow to engraft) and any 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.

Usage in other cancers

In addition to its use in bone marrow transplantation, total body irradiation has been explored as a

treatment modality A therapy or medical treatment (often abbreviated tx, Tx, or Tx) is the attempted remediation of a health problem, usually following a medical diagnosis. As a rule, each therapy has indications and contraindications. There are many different ...

for high-risk

Ewing sarcoma Ewing sarcoma is a type of cancer that forms in bone or soft tissue. Symptoms may include swelling and pain at the site of the tumor, fever, and a bone fracture. The most common areas where it begins are the legs, pelvis, and chest wall. In about ...

. 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 trials are prospective biomedical or behavioral research studies on human participants designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, diet ...

Fertility

Total body irradiation results in infertility in most cases, with recovery of gonadal function occurring in 10−14% of females. The number of pregnancies observed after

hematopoietic stem cell transplantation Hematopoietic stem-cell transplantation (HSCT) is the transplantation of multipotent hematopoietic stem cells, usually derived from bone marrow, peripheral blood, or umbilical cord blood in order to replicate inside of a patient and to produce ...

involving such a procedure is lower than 2%.

Fertility preservation Fertility preservation is the effort to help cancer patients retain their fertility, or ability to procreate. Research into how cancer, ageing and other health conditions effect reproductive health and preservation options are growing. Specifically ...

measures mainly include cryopreservation of ovarian tissue,

embryos An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...

oocyte An oocyte (, ), oöcyte, or ovocyte is a female gametocyte or germ cell involved in reproduction. In other words, it is an immature ovum, or egg cell. An oocyte is produced in a female fetus in the ovary during female gametogenesis. The femal ...

s. Gonadal function has been reported to recover in less than 20% of males after TBI.

References

{{authority control Transplantation medicine Radiobiology