Simultaneous optimization of beam orientations and beam weights in conformal radiotherapy

A methodology for the concurrent optimization of beam orientations and beam weights in conformal. radiotherapy treatment planning has been developed a nd tested on a cohort of five patients. The algorithm is based on a beam-we ight optimization scheme with a downhill simplex optimization engine. The u se of random voxels in the dose calculation provides much of the required s peed up in the optimization process, and allows the simultaneous optimizati on of beam orientations and beam weights in a reasonable time. In the imple mentation of the beam-weight optimization algorithm just 10% of the origina l patient voxels are used for the dose calculation and cost function evalua tion. A fast simulated annealing algorithm controls the optimization of the beam arrangement. The optimization algorithm was able to produce clinicall y acceptable plans for the five patients in the cohort study. The algorithm equalized the dose to the optic nerves compared to the standard plans and reduced the mean dose to the brain stem by an average of 4.4% (+/-1.9, 1 SD ), p value = 0.007. The dose distribution to the PTV was not compromised by developing beam arrangements the simultaneous optimization of beam orienta tions via the optimization algorithm. In conclusion, the simultaneous optim ization of beam orientations and beam weights has been developed to be rout inely used in a realistic time. The results of optimization in a small coho rt study show that the optimization can reliably produce clinically accepta ble dose distributions and may be able to improve dose distributions compar ed to those from a human planner. (C) 2001 American Association of Physicis ts in Medicine.