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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