Purpose: To efficiently select high-quality coplanar or non-coplanar beam orientations for IMRT treatments while formally and explicitly incorporating the effect of the selected beam orientations on the quality of the dose distribution obtained by the treatment plan optimization model.
Methods: Beam orientation models consider a discrete set of potential coplanar and/or non-coplanar beam locations around the patient. A new greedy algorithm is proposed to solve a model that integrates beam orientation optimization (BOO) and fluence map optimization (FMO). The algorithm iteratively adds beams to a FMO model. In each iteration, an attractiveness measure is associated with each remaining candidate beam orientation. This attractiveness measure is based explicitly on an optimal dose distribution that allows only the currently selected set of beams to be used. Several alternate attractiveness measures are considered which use either first-order information or both first and second-order information. Performance of the algorithm was assessed on a clinical lung cancer case.
Results: The developed beam selection algorithm was applied to a lung cancer case using either coplanar beams or both coplanar and non-coplanar beams. In the coplanar case, beam orientations were found that produce a superior dose distribution to that using an equal number of equi-spaced beams. In the non-coplanar case it was found that fewer beams were needed to produce a dose distribution of comparable quality to that found in the coplanar case.
Conclusions: The developed solution approach showcases the potential benefits of integrating different steps in the treatment plan optimization process. By integrating the BOO and FMO models, treatment plan quality was explicitly incorporated into the beam selection process. BOO can be automated and implemented efficiently, which eliminates the guesswork involved in manually adjusting beam orientations in IMRT treatment planning.
Keywords: Cancer; Dosimetry; Electric measurements; Intensity modulated radiation therapy; Lungs; Medical treatment planning; Radiation therapy; Radiation treatment; Solution processes.
© 2012 American Association of Physicists in Medicine.