4.3 - Immobilisation Devices

List in order of increasing reproducibility, the various setup/immobilisation techniques and devices used on your linac.

The reproducibility of treatment is dependent on the degree of immobilisation. Treatments which have less reproducibility have a higher tolerance, and this reduction in accuracy is compensated for by an enlargement of the planning target volume (PTV).

Least Accurate

Breast board (1 cm tolerance)

Somewhat Accurate

Vacbag immobilisation (7 mm tolerance)

Moderately Accurate

Prostate treatments - using wingboard, kneefix, footfix with indexing (5 mm tolerance)

Most Accurate

Thermoplastic mask (3 mm tolerance)


Stereotactic immobilisation (1 mm tolerance)