TH‐CD‐209‐04: Fuzzy Robust Optimization in Intensity‐Modulated Proton Therapy Planning to Account for Range and Patient Setup Uncertainties

Abstract

Purpose:We propose to apply a robust optimization model based on fuzzy‐logic constraints in the intensity‐modulated proton therapy (IMPT) planning subject to range and patient setup uncertainties. The purpose is to ensure the plan robustness under uncertainty and obtain the best trade‐off between tumor dose coverage and organ‐at‐risk(OAR) sparing.Methods:Two IMPT plans were generated for 3 head‐and‐neck cancer patients: one used the planning target volume(PTV) method; the other used the fuzzy robust optimization method. In the latter method, nine dose distributions were computed ‐ the nominal one and one each for ±3mm setup uncertainties along three cardinal axes and for ±3.5% range uncertainty. For tumors, these nine dose distributions were explicitly controlled by adding hard constraints with adjustable parameters. For OARs, fuzzy constraints that allow the dose to vary within a certain range were used so that the tumor dose distribution was guaranteed by minimum compromise of that of OARs. We rendered this model tractable by converting the fuzzy constraints to linear constraints. The plan quality was evaluated using dose‐volume histogram(DVH) indices such as tumor dose coverage(D95%), homogeneity(D5%‐D95%), plan robustness(DVH band at D95%), and OAR sparing like D1% of brain and D1% of brainstem.Results:Our model could yield clinically acceptable plans. The fuzzy‐logic robust optimization method produced IMPT plans with comparable target dose coverage and homogeneity compared to the PTV method(unit: Gy[RBE]; average[min, max])(CTV D95%: 59 [52.7, 63.5] vs 53.5[46.4, 60.1], CTV D5% ‐ D95%: 11.1[5.3, 18.6] vs 14.4[9.2, 21.5]). It also generated more robust plans(CTV DVH band at D95%: 3.8[1.2, 5.6] vs 11.5[6.2, 16.7]). The parameters of tumor constraints could be adjusted to control the tradeoff between tumor coverage and OAR sparing.Conclusion:The fuzzy‐logic robust optimization generates superior IMPT with minimum compromise of OAR sparing.This research was supported by the National Cancer Institute Career Developmental Award K25CA168984, by the Fraternal Order of Eagles Cancer Research Fund Career Development Award, by The Lawrence W. and Marilyn W. Matteson Fund for Cancer Research, by Mayo Arizona State University Seed Grant, and by The Kemper Marley Foundation. eRA Person ID(s) for the Principal Investigator: 11017970 (Research Supported by National Institutes of Health)