Purpose: Multi‐criteria optimization (MCO) is implemented for planning lung cancer radiotherapy treatments to clarify patient‐specific tradeoffs and allow real‐time plan decision making. Methods: For four locally advanced lung cancer patients (P1–P4), a basis set of MCO plans are constructed and compared to plans determined from fixed‐objective (FO) optimization for organs at risk (OARs). All optimized plans include constraints on target‐D95>70 Gy and spinal cord Dmax<45 Gy. Five MCO basis plans are designed per patient through weight variation of four non‐zero dose‐volume objectives (DVOs) for ipsilateral lung (iLung), contralateral lung (cLung), heart, and esophagus. The five basis plans are optimized according to: (1) simultaneous minimization of four OAR‐DVOs and (2–5) weight variation for one OAR‐DVO. Results: Patient‐specific tradeoffs between OAR objectives are revealed with MCO which are not evident in FO‐optimization. For P1, MCO basis plans vary iLung‐V20 from 46% to 65% and show that V20<46% is not achievable; the FO iLung‐V20 is 54%. For P2,the FO‐plan trades off a 1% reduction in iLung‐V20 for a 29% increase in esophagus‐V20. An interpolated MCO plan, in this case, takes advantage of this tradeoff to reduce esophagus V20 by from 41% to 8%. P3 shows increasing heart‐V20 by 35% (from 20% to 55%) results in a 7% (34%‐27%) reduction in iLung‐V20. With P4, MCO reveals a tradeoff between the two lungs; varying iLung‐V20 from 23% to 30% corresponds to cLung‐V20 varying from 23% to 17%. The FO plan treats cLung up to the V20 objective (to 29%) without penalty. MCO shows the ability to reduce OAR dose‐volumes, but often led to increased PTV hotspots. Conclusion: Analysis of MCO plans clarifies conflicting objectives and exposes inherent limitations due to patient geometry. Real‐time planning is possible with a small set of MCO plans, and achieves plans which are superior to FO‐optimization. Supported by NIH P01‐CA‐116602 and Philips Medical Systems.