Selection of beam angles for radiotherapy of skull base tumours usingcharged particles

Abstract

The geometrical treatment configuration for skull base tumours is investigatedusing three different sources of information. First, an analysis of treatmentangle combinations for 50 patients treated with conventional conformalradiation therapy is performed. In a second step, nine treatment plans for ahypothetical heavy ion gantry were prepared. Finally, cylindrical projectionsof the organs at risk are introduced as a tool to analyse the distribution oftreatment angles as well as the treatment geometry for each patient. Theresults of the analysis for conventional therapy clearly show treatment anglecombinations that are preferably used. These findings are also supported bythe geometrical analysis using the cylindrical projections. The majority oftreatment angles for heavy ions also seem to be confined to those regions. Inone case, however, the sharp distal dose fall-off of the heavy ions allowed abeam direction outside these conventionally used regions. The advantages of aheavy ion gantry versus a fixed horizontal beam line are shown by comparisonof treatment plans for both systems. Treatment angle combinations aresuggested that should be accessible for any beam line design using eitherfixed beams or a gantry.