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Illustration of margin calculations. (a) CTV-to-PTVMinDose margin MD (ϕ,θ). The solid arrow indicates the margin (minimum separation) in the direction (ϕ,θ). (b) Right nodal volumes. Because they are adjacent to the prostate PTV, CTVNodes and PTVNodes share a common surface. Because the high dose region is centered on the PTV, the PTVNodesMinDose surface extends around both the PTV and right/left nodal volumes.
