To deliver a desired dose to the target, a certain amount of radiative energy has to cross its surface, depending on the size. That energy fluence cannot be reduced. What can be influenced is the pattern in which this energy is delivered. The process of treatment planning attempts to find a pattern that strikes a reasonable compromise between the three competing priorities: target coverage, target dose homogeneity, and sparing of the adjacent OARs. A TPS optimizer is essentially a black box to the user. A set of numbers (objectives) is provided as an input, resulting in an output (a dose distribution typically further reduced to a set of DVHs). Ideally, the inputs should be intuitive, and the black box should be sensitive and linear (e.g., allow for an easy shift in the priorities and direct proportionality between the change in the input and corresponding output).