SU‐E‐T‐856: Investigation of Fluence Parameterization Methods for PARETO Multi‐Objective Radiation Therapy Treatment Planning Software

Purpose: To determine the best parameterization of fluence modulation for PARETO (Pareto‐Aware Radiotherapy Evolutionary Treatment Optimization) multi‐objective treatment planningsoftware, as judged by the complexity of each parameterization, the efficiency, and the quality of the plans produced. Methods: PARETO simultaneously optimizes the number of beams, beam orientations, and fluence modulation. For this investigation, we have tested four fluence parameterizations on a paraspinal tumour phantom and a spine patient data set using a pre‐determined number of beams. The first method applies linear gradients over the projection of Planning Target Volume (PTV) in the beam's‐eye‐view plane. The second method applies the two‐dimensional inverse cosine transform of a few low‐frequency parameters. Another method interpolates between the intensities of a coarse grid of square beamlets. Also, an isodose‐based contour method defines regions on the fluence maps that are assigned different intensities. Methods which produce plans of the best quality (as judged by dose‐volume histograms) will have a similar distribution of non‐dominated solutions. The complexity of each parameterization is determined by the number of parameters, and the efficiency is determined by the run time. Results: For both geometries, we found that the set of non‐dominated solutions of each parameterization overlapped in the projection of the PTV conformity fitness function and the quadrature‐averaged Organs‐At‐Risk (OAR) fitness function. The beam group and cosine transform methods produced some plans which did slightly better in simultaneously achieving good PTV conformity and OAR dose sparing. The cosine transform and linear gradient methods proved to be the most efficient. The cosine transform method also has the least number of parameters per beam. Conclusions: We have found that several different parameterizations of fluence modulation produce non‐dominated solutions of similar quality. The cosine transform method is the best choice for efficiently producing solutions that do well in PTV conformity and OAR sparing.