A system for determining a radiation treatment plan (P[CPS"]) for a treatment volume associated with at least one target and at least one organ-at-risk, the system comprising: a data processor configured to calculate, for each of at least one delivery direction, a radiation dose to be delivered to the at least one target, thus obtaining a description of how an amount of radiant energy from a radiation source shall be distributed over a projection area by executing the consecutive steps: receiving a current fluence map defining a radiation dose to be delivered to the at least one target; and receiving a current control-point sequence describing machine settings for a collimator associated with the radiation source, the machine settings defining at least one parameter for an output beam of radiation from the radiation source, characterized in that the data processor is configured to calculate, for each of the at least one delivery direction, the radiation dose to be delivered to the at least one target, by executing the further consecutive steps: determining an updated fluence map (FM') and an updated control-point sequence (CPS') based on the current fluence map, the current control-point sequence and an objective function quantifying at least one quality of the radiation dose with respect to a predefined goal; determining a further updated control-point sequence (CPS") based on the updated control-point sequence (CPS') and the updated fluence map (FM'), the further updated control-point sequence (CPS") describing how, with respect to an error-minimizing function, to adjust the machine settings to approximate an amount of radiant energy defined by the updated control-point sequence (CPS') and the updated fluence map (FM'), determining a further updated fluence map (FM") based on the updated fluence map (FM'), the updated control-point sequence (CPS') and the further updated control-point sequence (CPS"), checking if a stopping criterion is fulfilled; if so: stopping the process, and producing an output radiation treatment plan (P[CPS"]) based on the further updated control-point sequence (CPS");and otherwise: setting the further updated fluence map (FM"), or zero, to the current fluence map, setting the further updated control-point sequence (CPS") to the current control-point sequence; and returning to step. receiving a current fluence map defining a radiation dose to be delivered to the at least one target; and receiving a current control-point sequence describing machine settings for a collimator associated with the radiation source, the machine settings defining at least one parameter for an output beam of radiation from the radiation source, determining an updated fluence map (FM') and an updated control-point sequence (CPS') based on the current fluence map, the current control-point sequence and an objective function quantifying at least one quality of the radiation dose with respect to a predefined goal; determining a further updated control-point sequence (CPS") based on the updated control-point sequence (CPS') and the updated fluence map (FM'), the further updated control-point sequence (CPS") describing how, with respect to an error-minimizing function, to adjust the machine settings to approximate an amount of radiant energy defined by the updated control-point sequence (CPS') and the updated fluence map (FM'), determining a further updated fluence map (FM") based on the updated fluence map (FM'), the updated control-point sequence (CPS') and the further updated control-point sequence (CPS"), checking if a stopping criterion is fulfilled; if so: stopping the process, and producing an output radiation treatment plan (P[CPS"]) based on the further updated control-point sequence (CPS");and otherwise: setting the further updated fluence map (FM"), or zero, to the current fluence map, setting the further updated control-point sequence (CPS") to the current control-point sequence; and returning to step. stopping the process, and producing an output radiation treatment plan (P[CPS"]) based on the further updated control-point sequence (CPS");and otherwise: setting the further updated fluence map (FM"), or zero, to the current fluence map, setting the further updated control-point sequence (CPS") to the current control-point sequence; and returning to step. setting the further updated fluence map (FM"), or zero, to the current fluence map, setting the further updated control-point sequence (CPS") to the current control-point sequence; and returning to step.