OPTIMIZATION OF BEAM ORIENTATION IN RADIOTHERAPY USING PLANAR GEOMETRY

This paper proposes a new geometrical formulation of the coplanar beam orientation problem combined with a hybrid multiobjective genetic alg orithm. The approach is demonstrated by optimizing the beam orientatio n in two dimensions, with the objectives being formulated using planar geometry. The traditional formulation of the objectives associated wi th the organs at risk has been modified to account for the use of comp lex dose de:livery techniques such as beam intensity modulation. The n ew algorithm attempts to replicate the approach of a treatment planner whilst reducing the amount of computation required. Hybrid genetic se arch operators have been developed to improve the performance of the g enetic algorithm by exploiting problem-specific features. The multiobj ective genetic algorithm is formulated around the concept of Pareto op timality which enables the algorithm to search in parallel for differe nt objectives. When the approach is applied without constraining the n umber of beams, the solution produces an indication of the minimum num ber of beams required. It is also possible to obtain nondominated solu tions for various numbers oi beams, thereby giving the clinicians a ch oice in terms of the number of beams as well as in the orientation of these beams.