FEW-FIELD RADIATION-THERAPY OPTIMIZATION IN THE PHASE-SPACE OF COMPLICATION-FREE TUMOR CENTRAL

The phase space of P-+, describing the probability of achieving tumor control without causing severe complications in normal tissues, has be en investigated for three different clinically relevant treatment geom etries. These include tumors in the head and neck region, thorax, and pelvis. Some general conclusions about the shape and properties of the P-+ phase space are given for the selected target volumes. The use of three different radiation beam types-strictly homogeneous, wedged, an d generally nonuniform beams-has been investigated and the considerabl e differences in the P-+ phase space are shown. One conclusion is that the exact selection of beam entry direction becomes gradually less im portant as the number of beam portals becomes larger. One of the most important results is that use of appropriately selected nonuniform bea m profiles reduces the number of necessary beam portals to such a low level that the treatment technique becomes simple and reliable at the same time as the probability of achieving tumor control without severe complications is almost as high as with an unlimited number of beams This means that most ordinary treatment units equipped with beam compe nsating filters can be used for closely optimal radiation therapy. (C) 1995 John Wiley and Sons, Inc.