FIG 4.

OARs contoured far outside the dose volume are likely not to be encompassed by the shell discretization (Fig 3). Such remainder volume is assumed to be low-dose and added artificially to the differential DVH of the last (ie, outermost) OAR shell (upper plot). The remainder volume is distributed in the same manner as the shell volume—according to the kernel. This correction ensures that the cumulative DVH prediction (lower plot) reflects the total OAR volume as quoted in the TPS. Note the relatively low dose range over which this correction differs from the uncorrected DVH. DVH, dose-volume histogram; OAR, organs-at-risk.