A method is proposed for evaluating the robustness of a radiotherapy treatment plan. The method comprises, defining a number of scenarios, each comprising one or more errors for each fraction of the plan, including interfractional and/or intrafractional errors, and calculating a dose distribution resulting from the scenario； The robustness of the plan is then evaluated based at least one of the following i. the probability of fulfilling a set of clinical goals estimated as the clinical goal fulfillment over the scenarios ii. the range of DVH values over the scenarios iii. dose statistics for dose distributions defined as voxel-wise aggregates over the scenario doses
