Feasibility study of beam orientation class-solutions for prostate IMRT
DVH spectra of OARs and PTV for a set of clinically relevant nondominated plans in the Pareto front. The result of a multiobjective optimization is a set of plans (Pareto front) describing the “optimal of the optimized plans,” i.e., no objective can be improved without degrading another one.
Angular beams distribution for all plans of the Pareto front. The length of the radial segment in the above graphs represents the frequency of occurrence of the corresponding direction. Directions that are “preferred” during the optimization are identified with optimal directions. Presented are plans with three and five to nine beams.
The beam configuration of the most selected plan, for each individual case. Analysis of five-beam plans show that small deviations occur between plans considered optimal for each individual case. Similar results have been obtained for three and six to nine beams.
Distributions of beam angles for three and five to nine beams, respectively. The shaded lines represent directions found in individual cases and the top bold lines represent the directions identified as the class-solutions. The numbers in parenthesis summarize the gantry variation ranges of the corresponding beams.
Comparison of plans with optimized and class-solution plans. (a) Pareto fronts obtained by the two methods are identical for small values. (b) DVHs of class-solution plan (broken line) and optimized plan show that similar plans can be obtained by the class-solution without the use of a beam optimization procedure.
Comparison of class-solution plans and optimized plans for nine beams. (a) Pareto fronts (b) DVHs. Pareto fronts obtained with class-solution directions reproduce results obtained with full optimization, concentrating solution to clinically relevant small values, suggesting that a class-solution initialization for beam orientation optimization in IMRT can provide a priori good plans and thus reduce computation times.
Dose limits and volume limits used as constraints for OARs. The prescribed dose was to the PTV and to the OARs. For each OAR, two constraints are imposed: (a) the maximum dose and (b) a specified volume should not receive a dose greater than the limit dose.
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