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Causes of differences between TPS &

measured dose

Source

Unintentional Errors

Accepted Limitations

TPS

Beam data incorrectly measured

such as small field output factors, MLC

Transmission

Accepted TPS Beam Model Limitations ex.T&G

modelling inaccurate

Settings changed accidently ex.

gantry resolution for VMAT calculation

Continuous treatment segmented into static fields

at a pre-set gantry resolution

Linac

Data transfer errors

Dynamic Gantry Tolerance = 0.5°

Dynamic MU Tolerance = 0.2 MU

Linac component fall’s out of

specification (MLC calibration,

Energy, Flatness/Symmetry)

Dynamic MLC Tolerance = 5mm

Tolerance on Symmetry/Flatness with rotation and

@ low DR’s

Tolerance on MLC calibration