Total Body Irradiation (TBI)
Lung Blocks used to reduce dose to lung
Total body irradiation (TBI) involves irradiation of the entire body. It is typically used in conjunction with high dose chemotherapy in adult and pediatric patients undergoing stem cell transplantation for leukemias, lymphomas and other hematologic conditions.
The purpose of TBI is to eradicate remaining cancer cells and to cause immunosuppression (depression of the immune system). Immunosuppresion is required to help reduce the risk of rejection of transplanted tissue. Since the immune cells of the body are widely dispersed, irradiation of the entire body is indicated.
Although the entire body is irradiated, care is taken to reduce the dose to the underlying normal lung tissue. This is done with the use of customized lung blocks fabricated with low-melting point metal alloy known as “cerrobend”. These blocks are carefully placed over the lungs at the time of treatment.
TBI treatment typically is delivered twice daily over 3 days. However, a variety of other approaches may be used depending on the tumor site and the individual protocol. A current multiple myeloma TBI regimen, for example, utilize a single fraction of 2 Gy. In most protocols, however, the total dose is 12 Gy.
IM-TBI plan. Note sparing of brain, lung and liver.
Increasing interest has recently been focused on the application of intensity modulated radiation therapy (IMRT) in patients undergoing TBI, a technique known as intensity modulated TBI (IM-TBI). In this approach, which remains experimental at the present time, sophisticated treatment planning computers are used to focus the radiation dose preferentially on the bone marrow, reducing dose delivered to adjacent critical tissues.
Dr. Mundt and his former colleagues at the University of Chicago have explored the feasibility of IM-TBI and it is hoped that clinical trials will evaluate the benefits of this technique in the coming years.
Click here to view a copy of their most recent study.