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Unresolved issues with electron pencil beam
models
Dublin 2018
16
PB methods assume Gaussian characteristics of the incident beam. Hence,
influence from “non Gaussian” features (collimator scattering, etc) yield profile
errors and make output factors hard to calculate (has to be table lookup driven).
Penumbra modeling through manipulation of incident pencil width may wash
out effects of heterogeneities.
Requires homogeneous energy and directional distribution over the field.
Beam modeling:
Heterogeneities are well modeled at the first part of the depth range (since
voxels are larger than the FE pencil width).
At the end of the electron range, effects of localized heterogeneities (smaller
than the FE pencil width using semi-infinite slab approximation) get washed
out PB by models. “Redefinition” and “phase space evolution” models fix that,
to the cost of CPU&memory…
Heterogeneities: