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Conclusions
April 2017
47
The results from this study show that contrary to the popular
perception, conventional photon dose calculation using water with
relative electron densities produces dose distributions that are much
closer to Monte Carlo calculated dose-to-medium distributions than to
dose-to-water distributions converted using mass stopping-power ratios
of water to bone…
… explained by the fact that the photon dose deposition depends
mainly on the electron density since the predominant mode of
interaction is Compton scattering for photon beams of radiotherapy
interest.
Thus, the dose deposition scaled based on the relative electron density
is effectively dose to medium (with the corresponding electron density),
as implemented in many commercial treatment planning dose
algorithms in spite of their initial intentions or claimed applications.
Ma and Li, 2011