A mixed-encoding genetic algorithm with beam constraint for conformal radiotherapy treatment planning

In this paper we propose a new hierarchical evolutionary algorithm that com bines binary encoding and Boating-point encoding to automatically select th e beam directions and determine the weights of the selected beams. With tra ditional optimization methods the beam directions are fixed a priori by the operator in recognition of the fact that computer selection of beam direct ions is a difficult problem. In this investigation, we used a hybrid-encodi ng scheme. The binary encoding part of each chromosome was used to select t he beam directions, and its corresponding floating-point encoding part of t he same chromosome was used to determine the weights of those selected beam s. Before beginning the optimization process, we set a constraint on the nu mber of the beam directions we wanted in the final solution. We present thr ee examples to verify this method. These examples differ with each other in tumor sites, problem sizes, and optimization parameters. Three-dimensional optimization results and statistical data showed that this method is feasi ble. We think this method can be easily extended to solve more complex targ et problems (such as nonconvex target problems). (C) 2000 American Associat ion of Physicists in Medicine. [S0094-2405(00)01511-X].