Characterization of dose distributions through the max and mean dose concept.

A new approach for the determination of the equivalent uniform dose (EUD) for inhomogeneously irradiated normal organs is developed and tested. The EUD is calculated as a linear combination of the maximum and the mean dose: EUD = alphaDmax + (1 - alpha)D. We call this the max & mean model. The values of alpha are determined by a fit to the Emami tables for complication levels of 5% and 50%. The predictions of the max & mean model are compared with the Emami tables for different treatment volume fractions. The quality of the fit is also compared with the well-known power-law EUD model. The max & mean model makes it possible to make useful predictions of the EUD for organs having an organization anywhere between serial and parallel. The model can be fitted to the Emami tables within the same error range as the widely used power-law model (about 10%) and can be integrated into linear multicriteria optimization algorithms for planning of intensity-modulated radiotherapy.