A method of beam angle optimization for an IMRT radiotherapy treatment, the method comprising: providing a patient model including one or more planning target volumes, PTVs, the one or more PTVs including a first PTV; defining a delivery coordinate space, DCS, having a plurality of vertices, each respective vertex defining a respective beam's eye view, BEV, plane; for each respective BEV plane of a respective vertex: for each respective pixel of the respective BEV plane: evaluating a dose of the first PTV from a respective beamlet originating from the respective vertex and passing through the respective pixel of the respective BEV plane; and evaluating a respective BEV score of the respective pixel of the respective BEV plane based at least in part on the dose of the first PTV from the respective beamlet; determining a threshold BEV score for the first PTV based on the BEV scores of the pixels of the BEV planes; for each respective BEV plane of the respective vertex: determining one or more BEV regions by comparing the respective BEV score of each respective pixel to the threshold BEV score, wherein pixels within the one or more BEV regions have BEV scores greater than or equal to the threshold BEV score; and determining a BEV region connectivity manifold for the first PTV representing connections between BEV regions of adjacent vertices; characterized by : selecting a plurality of optimal field geometries for the IMRT radiotherapy treatment based at least in part on the BEV region connectivity manifold for the first PTV. providing a patient model including one or more planning target volumes, PTVs, the one or more PTVs including a first PTV; defining a delivery coordinate space, DCS, having a plurality of vertices, each respective vertex defining a respective beam's eye view, BEV, plane; for each respective BEV plane of a respective vertex: for each respective pixel of the respective BEV plane: evaluating a dose of the first PTV from a respective beamlet originating from the respective vertex and passing through the respective pixel of the respective BEV plane; and evaluating a respective BEV score of the respective pixel of the respective BEV plane based at least in part on the dose of the first PTV from the respective beamlet; evaluating a dose of the first PTV from a respective beamlet originating from the respective vertex and passing through the respective pixel of the respective BEV plane; and evaluating a respective BEV score of the respective pixel of the respective BEV plane based at least in part on the dose of the first PTV from the respective beamlet; determining a threshold BEV score for the first PTV based on the BEV scores of the pixels of the BEV planes; for each respective BEV plane of the respective vertex: determining one or more BEV regions by comparing the respective BEV score of each respective pixel to the threshold BEV score, wherein pixels within the one or more BEV regions have BEV scores greater than or equal to the threshold BEV score; and determining a BEV region connectivity manifold for the first PTV representing connections between BEV regions of adjacent vertices; characterized by : selecting a plurality of optimal field geometries for the IMRT radiotherapy treatment based at least in part on the BEV region connectivity manifold for the first PTV. <EOS>