Total Body Irradiation

During the 60’s was achieved a milestone in the treatment of haematopoietic system diseases through the development of high-dose therapy followed by stem cell transplantation. The total body irradiation (TBI) is usually part of an interdisciplinary comprehensive treatment and is used in the context of high-dose therapy in certain leukemias, in lymphomas, in bone marrow or blood stem cell transplantation. TBI brings an important contribution to conditioning of the patient, before blood stem cell transplantation. The aim of the conditioning is the destruction of the tumor cells, the myeloablation and the suppression of the immune system to allow a proliferation in the donor cells. The individual period of therapy is perfectly timed to ensure the best treatment.

The applied dose with TBI treatment may vary depending on the particular indication and the chemotherapy protocol used. Usual total doses are in the range of 8-12 Gy, divided in dose-fractions of 2 Gy, where the patient is irradiated twice a day with at least 7 hours time-interval between fractions. The only organs at risk in the whole body irradiation are the lungs, with a well defined dose-limit. An overdose in the lungs can developed pneumonitis and fibrosis as a result of their high sensitivity to radiation. Therefore, when the prescribed dose is in the range between 10 to 12 Gy, the total dose in the lungs is reduced to an average of 9 Gy using specific lung blocks for each patient.

The target volume in TBI is the entire body, including the skin. In conventional radiotherapy the target volume is limited to a size of 40 cm x 40 cm. In order to cover the whole body, the patient is positioned on a special bed, which stands directly on the floor. The distance to the focus of the linear accelerator is thus increased to 219 cm. By an arc-based radiation, which rotates from 320° to 60°, the entire body can be irradiated in about 5 minutes. The treatment is carried out using 2 arcs, one will irradiate the supine position and the other the prone position of the patient. During the irradiation, nine semiconductors are positioned directly on the patient-skin to monitor the dose in defined anatomical points. To compensate the dose increase in the first 1.5 cm of the body, a spoiler is positioned between the spotlight and patient.


Figure 1: schematic drawing of TBI setup

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last modified: 21-Apr-15
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