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Conclusion
•Several different methods are available when characterizing, parameterizing and integrating
pencil kernels.
•Generally, the pencil kernel implementation is associated with a number of approximations
and limitations, related to the actual photon beam or the dose calculation object.
Some of these errors can be minimized through more advanced modelling while other errors,
mainly related to tissue heterogeneities, require algorithms employing explicit 3D-modelling.
•Pencil kernel algorithms are widely used in clinical treatment planning systems for photon
dose calculations. Their popularity is related to the fact that they offer a good
compromise
between flexibility, accuracy and speed. For this reason they are the dose engine of choice
used in plan optimisation calculations.