Role of non-coplanar beams in IMRT

We have investigated the benefits of using non-coplanar beams with optimized directions for intensity modulated radiation therapy. We have considered three typical cases of localized prostate cancer, nasopharyngeal cancer, and paraspinal treatment. Nine fields were used for each treatment. For all cases, three types of treatment plan optimization were done: (1) nine uniformly spaced coplanar beams with optimized beam intensity profiles; (2) beam orientations and beam profiles were optimized, but only coplanar beams were allowed; (3) similar to (2), except that non-coplanar beams were allowed during beam orientation optimization. Simulated annealing was used for beam orientation optimization and an iterative optimization algorithm was used for beam intensity profile optimization. For the localized prostate case, all three types of optimization described above resulted in a dose distribution of similar quality. For the nasopharyngeal case, optimized non-coplanar beams provided a significant improvement in GTV coverage. For the paraspinal case, orientation optimization of non-coplanar beams resulted in significant improvement of kidney sparing and in increased GTV coverage. It is concluded that the use of non-coplanar beams with optimized orientations presents a viable option to improve target coverage and critical structure sparing in complicated cases.