Beam orientation optimization in intensity-modulated radiation treatment planning

Beam direction optimization is an important problem in radiation therapy. I n intensity modulated radiation therapy (IMRT), the difficulty for computer optimization of the beam directions arises from the fact that they are cou pled with the intensity profiles of the incident beams. In order to obtain the optimal incident beam directions using iterative or stochastic methods, the beam profiles ought to be optimized after every change of beam configu ration. In this paper we report an effective algorithm to optimize gantry a ngles for IMRT. In our calculation the gantry angles and the beam profiles (beamlet weights) were treated as two separate groups of variables. The gan try angles were sampled according to a simulated annealing algorithm. For e ach sampled beam configuration, beam profile calculation was done using a f ast filtered backprojection (FBP) method. Simulated annealing was also used for beam profile optimization to examine the performance of the FBP for be am orientation optimization. Relative importance factors were incorporated into the objective function to control the relative importance of the targe t and the sensitive structures. Minimization of the objective function resu lted in the best possible beam orientations and beam profiles judged by the given objective function. The algorithm was applied to several model probl ems and the results showed that the approach has potential for IMRT applica tions. (C) 2000 American Association of Physicists in Medicine. [S0094-2405 (00)00806-3].