A method of determining a radiation treatment plan for concurrent treatment of multiple target volumes within a patient using a radiation treatment system, the method comprising: receiving, at a computer system, a first desired value for a relative volumetric coverage at a first lower dose objective for a first target volume within the patient, and a second desired value for a relative volumetric coverage at a second lower dose objective for a second target volume within the patient; obtaining, by the computer system, a cost function including a first term with a first weight and a second term with a second weight, the first term relating to a first difference between an average relative volumetric coverage and the relative volumetric coverage for the first target volume, the second term relating to a second difference between the average relative volumetric coverage and the relative volumetric coverage for the second target volume, the average relative volumetric coverage being an average of the relative volumetric coverage for the first target volume and the relative volumetric coverage for the second target volume; for each of a plurality of iterations: determining, by the computer system, a set of control point sequence for the radiation treatment system; evaluating, by the computer system, the relative volumetric coverage for the first target volume and the relative volumetric coverage for the second target volume based on the set of control point sequence; evaluating, by the computer system, a current value of the cost function based on the evaluated relative volumetric coverage for the first target volume and the evaluated relative volumetric coverage for the second target volume; and updating, by the computer system, the set of control point sequence based on the current value of the cost function; and determining, by the computer system, an optimal radiation treatment plan by performing the plurality of iterations, wherein the optimal radiation treatment plan includes an optimal set of control point sequence corresponding to an optimal value for the cost function that meets a pre-determined convergence criterion. receiving, at a computer system, a first desired value for a relative volumetric coverage at a first lower dose objective for a first target volume within the patient, and a second desired value for a relative volumetric coverage at a second lower dose objective for a second target volume within the patient; obtaining, by the computer system, a cost function including a first term with a first weight and a second term with a second weight, the first term relating to a first difference between an average relative volumetric coverage and the relative volumetric coverage for the first target volume, the second term relating to a second difference between the average relative volumetric coverage and the relative volumetric coverage for the second target volume, the average relative volumetric coverage being an average of the relative volumetric coverage for the first target volume and the relative volumetric coverage for the second target volume; for each of a plurality of iterations: determining, by the computer system, a set of control point sequence for the radiation treatment system; evaluating, by the computer system, the relative volumetric coverage for the first target volume and the relative volumetric coverage for the second target volume based on the set of control point sequence; evaluating, by the computer system, a current value of the cost function based on the evaluated relative volumetric coverage for the first target volume and the evaluated relative volumetric coverage for the second target volume; and updating, by the computer system, the set of control point sequence based on the current value of the cost function; and determining, by the computer system, a set of control point sequence for the radiation treatment system; evaluating, by the computer system, the relative volumetric coverage for the first target volume and the relative volumetric coverage for the second target volume based on the set of control point sequence; evaluating, by the computer system, a current value of the cost function based on the evaluated relative volumetric coverage for the first target volume and the evaluated relative volumetric coverage for the second target volume; and updating, by the computer system, the set of control point sequence based on the current value of the cost function; and determining, by the computer system, an optimal radiation treatment plan by performing the plurality of iterations, wherein the optimal radiation treatment plan includes an optimal set of control point sequence corresponding to an optimal value for the cost function that meets a pre-determined convergence criterion.