A computer-based method for generating an improved radiation therapy treatment plan for a treatment volume having a target and an organ-at-risk. The method includes a step of accessing an existing radiation therapy treatment plan from a memory of a computer, a dose distribution of the existing radiation therapy treatment plan serving as a reference dose distribution and performing machine parameter optimization on the existing radiation therapy treatment plan with the computer by pursuing an optimization goal to minimize doses to the organ-at-risk, thereby generating the improved radiation therapy treatment plan.
