Physical optimization

One of the two prerequisites for the clinical application ofIMRTwas the development of inverse planning strategies - simply because the available forward planning strategies couldnotbe applied to theoptimizationof the enormous number of treatment parameters suddenly required for the efficient delivery of intensity modulatedtreatmentfields. Theconceptof 'physical optimization' was the first strategy implemented in commercial inverse planning systems and still currently is the 'working horse' of most available planning platforms. Even the modifications of the original concept often referred to as 'biological optimization', described below, basically keep the same logical structure of the optimization while only the mathematical formulation of the objectives of the optimization is modified. One common factor of both approaches is the selection of the energy fluence profiles for a pre-selected set of beam ports as the only treatment parameters to be optimized in the planning process. We consider the respective physical optimization as the current 'standard model' of IMRT optimization and review some of its detailed features later. The more recent extensions of this concept that attempt to include further physical degrees of freedom in the optimization process are described. The reader should be aware that the following brief discussion cannot aim to reflect all aspects of the physical optimization approach for IMRT.Aby farmore complete review about inverse planning and IMRT optimization and their details can be found in the papers of T. Bortfeld [1, 2] and S.Webb [3, 4].