ABSTRACT
PURPOSE: PARETO (Pareto-Aware Radiotherapy Evolutionary Treatment Optimization) is a novel multiobjective treatment planning system that performs beam orientation and fluence optimization simultaneously using an advanced evolutionary algorithm. In order to reduce the number of parameters involved in this enormous search space, we present several methods for modeling the beam fluence. The parameterizations are compared using innovative tools that evaluate fluence complexity, solution quality, and run efficiency. METHODS: A PARETO run is performed using the basic weight (BW), linear gradient (LG), cosine transform (CT), beam group (BG), and isodose-projection (IP) methods for applying fluence modulation over the projection of the Planning Target Volume in the beam's-eye-view plane. The solutions of each run are non-dominated with respect to other trial solutions encountered during the run. However, to compare the solution quality of independent runs, each run competes against every other run in a round robin fashion. Score is assigned based on the fraction of solutions that survive when a tournament selection operator is applied to the solutions of the two competitors. To compare fluence complexity, a modulation index, fractal dimension, and image gradient entropy are calculated for the fluence maps of each optimal plan. RESULTS: We have found that the LG method results in superior solution quality for a spine phantom, lung patient, and cauda equina patient. The BG method produces solutions with the highest degree of fluence complexity. Most methods result in comparable run times. CONCLUSION: The LG method produces superior solution quality using a moderate degree of fluence modulation.
ABSTRACT
A beam orientation optimization (BOO) algorithm based on optimizing beam intersection volume (BIV) components within an Organ-at-Risk (OAR) is proposed to improve conventional intensity-modulated radiation therapy (IMRT). A simulated annealing algorithm was employed to search for the optimal set of five beam orientations (5-opt) which simultaneously minimize the BIV components within an OAR. The 5-opt plans were compared to standard 5, 7, and 9 equiangular-spaced beam plans (5-equi, 7-equi, 9-equi) for: (1) gastric (2) Radiation Therapy Oncology Group (RTOG) P-0126 prostate and (3) RTOG H-0022 oropharyngeal (Stage-III, IV) cancer patients. In the gastric case, the coplanar 5-opt plan reduced the right kidney V 20 Gy by 41.1%, 32.1%, and 29.5% compared to the 5-equi, 7-equi, and 9-equi plans. In the prostate case, the coplanar 5-opt plan improved rectal sparing over all standard plans with a reduction of the V 75 Gy, V 70 Gy, V 65 Gy, and V 60 Gy of 3.9%, 6.2%, 8.1%, and 10.6% compared to the 5-equi plan. In both oropharyngeal cases, the non-coplanar 5-opt plan substantially reduced the V 30 Gy and mean dose to the contralateral parotid compared to the 5-equi, 7-equi, and 9-equi plans: (Stage-III) 8.9%, 7.0%, 8.6% and 4.1 Gy, 2.5 Gy, 2.7 Gy (Stage-IV) 11.2%, 11.2%, 10.8% and 7.8 Gy, 7.9 Gy, 8.0 Gy. In conclusion, the method of optimizing BIV to produce substantial improvements in OAR sparing over conventional IMRT has been demonstrated to be robust for application to a variety of IMRT treatment sites.
