TBI is complicated in both theory and practice. This is a very simplified summary of the how it is implemented.
In order to to have room for the entire body in one radiation field, the distance from the source to the skin must be increased, which can be achieved by setting the source to irradiate horizontally such that it is as far as possible from the wall in the bunker. The patient can be positioned 3-4 m away in the other end of the bunker in the desired position. The patiet can lie, stand, or sit in the fetal position depending on the distance allowed by the source whether irradiating with opposing anteroposterior field, lateral field, or a combination.
At Oslo University Hospital, the patient lies down sometimes with slightly angled legs in a bed. Half-way through each fraction, the bed is turned 180 degrees. The patient is also changed for every other fraction between laying supine and laterally. The arms are positioned such that they compensate for 'missing' soft tissue in the lungs in the fractions where the lungs are not shielded. The lungs are shielded for fractions 3, 7, of 10 and the patient keeps their arms away from the anterior planes of the lungs during these fractions. Oslo University Hospital uses a moulded mat of VacFix® to give the best possible reproducible lateral position. To achieve full coverage of the skin, a device must be used that functions as a bolus (blanket of tissue-equivalent bolus) or, as at Oslo University Hospital, a shield of plexiglass in a suitable position between the patient and the source generating scatter electrons.
Simulation of TBI is done 1-2 weeks before treatment in a procedure known as a test shot or test fraction. The entire procedure can take up to 1.5 hours.
A VacFix® is made to stabilize the patient in the lateral position and is used for the fractions where the lungs are to be blocked out (fraction 3 and 7 of 10).
The patient will then complete a simulated treatment with a low dose (<0.1 Gy) with a series of dosimeters placed at relevant measuring points on the body.
X-ray images are taken of the patient in the lateral position in the VacFix® for contouring of lung blocks.
The treating doctor will draw the lung blocks on the X-ray image. These are drawn analogous to the lung blocks for a mantle field. Blocks follow the lower border of the fourth rib cranially, laterally 0.5–1 cm into the lung tissue, caudally turning 0.5–1 cm above the diaphragm, and medially 1–1.5 cm from the mediastinum/hilum into the lung tissue. The hilar contours are most visible on the right side. On the left side, the contours are drawn equivalent so that part of the lung in front of the heart and parts of the stomach are under the block.
- During treatment, the patient is admitted to the hospital at the latest the day before treatment. The patient should begin with antiemetic treatment (ondansetron 8 mg x 2 or equivalent) and fluids before the first fraction the evening before starting treatment. A serotonin antagonist is supplemented during treatment with other treatment, if necessary.
- Fluids and nausea treatment is constant during TBI treatment. Standard treatment for adults is 2 L NaCl 0.9 % and 2 L glucose 5 %, alternating with 40 mmol KCl per 1000 ml fluid.
- During this treatment, the patient will start serious bone marrow aplasia and should be handled both at the ward and treatment unit as extra susceptible to infection.
- The radiation bunker is washed before each afternoon fraction, and the device the patient is in contact with is washed with alcohol before treatment. The patient will be the last patient of the afternoon and the first patient the following morning.
- Additional protection for infection may be necessary such as isolation for neutropenia and the danger of infection upon contact.
- For fractions 3 and 7, the treating doctor will check and approve the positioning of the lung blocks.