Lecture 19: Total Body Irradiation

Are standard LINAC vaults big enough for TBI?

No

Whole-body lethal dose (50% population kill)

6-8 Gy

High dose TBI with megavoltage photon beams is frequently used to…

1. Destroy bone marrow and leukemic cells

2. Immunosuppress the patient prior to receiving a bone marrow transplant

What is the major organ at risk in TBI?

Lung

What are advantages of TBI over chemotherapy?

1. Homogeneous dose, independent of blood supply

2. No cross resistance with other agents

3. No hazards of handling, excreting detoxifying chemical agents

4. Dose can be tailored by blocking and boosting

How many times a day does a patient receive dose for TBI? What is the minimum time between fractions?

1 to 3 times a day with a minimum of 6 hours between fractions

What is the typical number of treatments for TBI? How much dose is delivered per fraction?

5-11 treatments with 125-225 cGy/fx

What percentage should dose homogeneity be for TBI?

10%

Why is the dose rate smaller for TBI?

When there is less dose rate, there is less radiation pneumonitis (typically 5-20 cGy/min)

What distance is necessary to provide a field length of 1.8 m (6 ft) for TBI?

distance greater than 3.3 m

What is a spoiler/ degrader used for in TBI?

increase superficial dose by eliminating buildup region

Commissioning and MU Calc differences for TBI and conventional radiotherapy?