term1 Definition1term2 Definition2term3 Definition3
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can be specified as a maximum permissible percentage variation from the average dose across the central 80% of the full width at half maximum of the beam profile in a plane transverse to beam axis
flatness
is usually specified for both transverse directions, each along the direction of collimator motion, for several field sizes, for a particular depth in a phantom, and for several gantry angles
symmetry
purpose
to ensure that the symmetry and flatness of the radiation beam are at acceptable limits
deviations may result in:
unacceptable high or low dose regions in irradiated areas
5 things that may result in unacceptable beam profiles
changes in beam energy, beam alignment, bending magnet functions, target positions, and flattening filter selection
tolerance for flatness:
non IMRT for photons:
non IMRT for electrons
IMRT for both electron and photon:
2%
3%
1%
tolerance for symmetry:
non IMRT:
IMRT:
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