1. Introduction
About 60 percent of cancer patients are treated with radiation at
some time during their course of treatment. Modern radiation
therapy treatment modalities such as intensity modulated radia-tion therapy (IMRT) are able to deliver dose that exquisitely con-forms to diseased tissue while sparing healthy tissue. Of ten these
treatments deposit dose in a complicated manner to produce steep,
three-dimensional dose gradients that conform to irregular
anatomical surfaces. The potential bene fi ts are greatly desirable,
including the reduction of side effects in normal tissue and the