FIG 2.

1D radial PTV shells discretize the dose volume. Strong dose anisotropies are handled by splitting each shell into in-field and out-of-field components, which are treated separately throughout the workflow. An OAR is thus discretized into regions defined by overlaps with the shells and the beam field (ie, OAR shells). Any OAR volume remaining outside the shells is assumed to be low-dose and will be used as a correction factor to the final DVH prediction (see DVH prediction). DVH, dose-volume histogram; OAR, organs-at-risk; PTV, planning target volume.