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Total and half-body irradiation




Introduction

Total body irradiation (TBI) is a special radiotherapeutic technique that delivers to a patient’s whole body a uniform dose using megavoltage photon beams. Such large field techniques encompass irradiation of the whole body, half body irradiation and total nodal irradiation. TBI is used primarily as part of a preparatory cytoreductive conditioning regimen prior to bone marrow transplantation. TBI is a complex treatment modality requiring strict adherence to specific quality assurance protocols, and often includes in vivo dosimetry at several locations on the patient’s body.


Important Principles

Cobalt-60 gamma rays or megavoltage x rays are used for TBI, applying either stationary beams with field sizes encompassing the whole patient, or moving beams with smaller field sizes in translational or rotational motion to cover the whole patient. Usually parallel-opposed irradiations are used and the patient’s position is switched between the two irradiations. TBI treatment techniques are carried out with treatment machines specially designed for total body irradiation, or by using conventional megavoltage radiotherapy equipment at large SSD. The TBI dose is generally prescribed to the midpoint at the level of the umbilicus. Uniformity of dose throughout the body is achieved with the use of bolus, partial attenuators, and compensators. Because the lung is an organ at risk, often additional lung shielding is applied during TBI.


Introduction to References

Various aspects of early techniques of TBI, including requirements for a QA programme, were summarised in the initial AAPM Report. More recent developments in the field of TBI can be found in J. Van Dyk’s Compendium, the Practical Radiotherapy Planning Textbook, the IAEA Handbook, and the Handbook of Radiotherapy Physics.