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6 Cards in this Set

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Define TBI
Total body irradiation

-Most commonly used as part of the conditioning regimen for bone marrow transplantation.
What are the typical techniques for TBI?
Bilateral technique: This technique involves bilateral fields (left and right lateral opposing fields) with the patient seated on a couch in a semi-fetal position.

- Compensators are needed for head and neck, lungs, and legs to achieve dose uniformity within approximately +- 10% along the sagittal axis of the body.

- Dose prescription is specified by the relevant protocol and, for bilateral technique, is usually at the midpoint of the body cross section at the level of umbilicus.

AP/PA technique: The patient is irradiated AP/PA by parallel-opposed fields while positioned in a standing upright position at the TBI distance.

-The standing AP/PA technique allows shielding of certain critical organs (lungs and brain) from excessive photon dose and boosting the dose to superficial tissues in the shadow of the blocks with electrons to makeup for the deficit.

-The AP/PA technique can also be adopted for treating small children in the reclining position.
What is the typical energy used for TBI TX?
6 MV should be used for patients with a thickness less than 35 cm. For a patient thickness greater than 35 cm, energies higher than 6 MV should be used to minimize the tissue lateral effect.
What do the compensators in TBIs compensate for?
Compensators are required to achieve dose uniformity along the body axis to within +- 10%.
What is in vivo dosimetry?
In vivo dosimetry check may be performed using TLDs or diodes placed on the patient's surface.

The measured dose should be compared with the expected doses at the surface under the dose buildup conditions.

An agreement of +-5% between calculated and measured doses is considered acceptable.
How do you implement a TBI program?
A TBI team should be formed which includes a radiation oncologist, medical physicist, medical dosimetrist, and radiation therapist.

Key members of this team should visit another institution that has an active TBI program to learn all aspects of the TBI procedure including patient measurements, patient setup, dosimetry, quality assurance procedures, and worksheets specifically designed for TBI.