Patient set-up and fixation

 
Accurate and repeatable patient setup is a pre-requisite for radiotherapy in order to limit the margin around the clinical target volume (CTV), i.e. the planning target volume (PTV), and consequently minimize the irradiation of healthy tissues responsible for early and late side effects.
If the CT is used not only for diagnostic purposes, a properly stored plane indexed tabletop shall belong to it on which the patient immobilizing devices can be fixed in a proper and reproducible way.
If the patient was positioned in conventional CT table, when planning-CT image was made, then the patient's organs and their relative positions change significantly during the treatment delivering, shown in Figure 1.

Figure 1: Patient set-up with different type of CT table; a. conventional CT table, b. treatment table

The most common set-up errors are:
- patient lies diagonally in the CT table (Figure 2.)
- patient fixation is not properly applied because the image set is not available for treatment planning (Figure 3.).

Figure 2.: Patient set-up error.

Figure 3.: The patient fixation isn’t properly used.