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The Uniformity Index UI which can be extracted from the natural volume
dose histogram (Anderson 1986), is defined as:
Uniformity Index UI
u(HD)
-
u(PD)
u(PD)
*
V(PD)
HD)
-
V(PD
= UI
With PD the prescription dose, HD the dose at half maximum of the peak at the high
dose side, V(PD-HD) the volume receiving a dose between PD and HD, V(PD) the
volume receiving at least the prescription dose PD and u(D)= D
-3/2
.
This uniformity index, thus, depends not only on the uniformity of the dose
distribution but also on the choice of the reference isodose. It expresses the
amount of the treatment volume which is concentrated between the prescription
dose, PD, and the high dose side of the peak, HD.