ADVANCED INTERACTIVE PLANNING TECHNIQUES FOR CONFORMAL THERAPY - HIGH-LEVEL BEAM DESCRIPTIONS AND VOLUMETRIC MAPPING TECHNIQUES

Purpose: To aid in design of conformal radiation therapy treatment pla ns involving many conformally shaped fields, this work investigates th e use of two methodologies to enhance the ease of interactive treatmen t planning: high-level beam constructs and beam's-eye view volumetric mapping. Methods and Materials: High-performance computer graphics run ning on various workstations using a graphical visualization system (A VS) have been used in this work. Software specific to this application has been written in standard FORTRAN and C languages. A new methodolo gy is introduced by defining radiation therapy ''fields'' to be compos ed of multiple beam ''segments.'' Fields can then be defined as higher -level entities such as arcs, tones, and other shapes. A ''segmental c one'' field, for example, is defined by a symmetry axis and a cone ang le, and can be used to rapidly place a series of beam segments that co nverge at the target volume, while reducing the degree of overlap else where. A new beam's-eye view (BEV) volumetric mapping technique is pre sented to aid in selecting the placement of conformal radiation fields . With this technique, the relative average dose within an organ of in terest is calculated for a sampling of isocentric, conformally shaped beams and displayed either as a ''globe,'' which can be combined with the display of anatomical surfaces, or as a two-dimensionally mapped p rojection. The dose maps from multiple organs can be generated, stacke d, or composited with relative weightings to aid in the placement of f ields that minimize overlap with critical structures. Results: The use of these new methodologies is demonstrated for prostate and lung trea tment sites and compared to conventional planning techniques. Discussi on: The use of many beams for conformal treatment delivery is difficul t with current interactive planning. The use of high-level beam constr ucts provides a means to quickly specify, place, and configure multipl e beam arrangements. The BEV volumetrics aids in the placing of fields , which minimize involvement with critical normal tissues. Conclusions : Early experience with the new methodologies suggest that the new met hods help to enhance (or at least speed up) the ability of a treatment planner to create optimal radiation treatment field arrangements.