What is the first step before a TBI patient enters the treatment room?
Prepare the treatment room by ensuring sterility, including reverse ventilation, sterile gowns and masks for therapists, and placing a gurney or TBI immobilization device in the room.
What must therapists wear during TBI setup to maintain a sterile environment?
Sterile gowns and masks.
What type of room environment is required for TBI setup?
A sterile room with reverse ventilation.
What equipment may be needed in the room for patient positioning during TBI?
A gurney or other TBI immobilization device.
What is an ideal anatomical landmark to use as an isocenter reference for TBI?
The umbilicus.
What is the standard collimator field size used for TBI?
40 cm by 40 cm.
What role does beam divergence play in TBI field setup?
Beam divergence is used to help cover the entire body beyond the 40 cm x 40 cm collimator opening.
Which patient positioning technique provides a more homogeneous dose distribution for TBI?
AP/PA (anterior-posterior/posterior-anterior) positioning.
What is an advantage of AP/PA positioning in TBI?
Easier shielding of critical structures and more consistent dose distribution.
What is a disadvantage of bilateral positioning in TBI?
Less dose homogeneity due to variable body density; requires compensating blocks.
Why might bilateral positioning still be chosen for TBI?
Improved patient comfort.
What is the alternative method to static beam setups in TBI?
Sweeping beam method.
What is the goal of dose uniformity in TBI?
+/- 10% of the prescribed dose throughout the body, with a best-case scenario of +/- 5%.
What are the typical dose prescriptions for TBI?
- High Dose: 13.2 Gy in 6 fractions over 3 days
- Standard Dose: 12 Gy in 6 fractions over 3 days
- Low Dose: 2 Gy in a single fraction
What are the dose-limiting structures in TBI?
The lungs and lenses of the eyes (limited to 10 Gy).
What is the purpose of TBI in stem cell or bone marrow transplantation?
To eradicate diseased marrow, suppress the immune system to reduce graft rejection, create space in the bone marrow, and destroy genetically abnormal cells.
Why is TBI considered a systemic radiation treatment?
Because it irradiates the entire body, unlike conventional localized radiation treatments.
What are some acute side effects of TBI?
- Nausea
- Vomiting
- Fatigue
- Headache
- Ocular dryness
- Mucositis
- Esophagitis
- Erythema
- Hyperpigmentation
- Diarrhea
- Fever
- Loss of appetite
What are some chronic complications from TBI?
- Sterility
- Cataracts
- Growth retardation
- Neurologic retardation
What is a theoretical modern method for delivering TBI with better critical structure sparing?
Using a tomotherapy unit (e.g., Halcyon), though it is complex and difficult to reproduce positionally for full-body planning.
To determine the distance the patient should stand from the collimator so that a 40 cm × 40 cm field size (at 100 cm from the source) covers their entire body length, you use the inverse divergence formula based on similar triangles:
