The present invention provides a method for updating and optimizing a treatment plan for radiotherapy. An initial treatment plan, calculated using a constraint-driven method, may be updated using a weighted-sum method, where Lagrange multipliers generated in the constraint method are reused as the weights for the weighted sum. This method results in acceptable updated treatment plans that are generated in a small fraction of the time taken to generate an entirely new treatment plan, reducing patient discomfort and ensuring the radiotherapy facility can treat more patients.
