A system for assisting in planning a focal therapy treatment of a structure within a patient body by applying a treatment quantity to a body region including the structure using one or more devices (4a,b,c; 403a,b,c), the devices (4a,b,c; 403a,b,c) being operated within the patient body in one or more device positions and in accordance with treatment parameters associated with the device positions, each device position being reached via an associated insertion point into the patient body, wherein the system comprises: - a constraint function generation unit (10; 406) configured to generate a constraint function representing clinical objectives relating to the treatment quantity, the constraint function depending upon at least one associated treatment parameter of each candidate device position of a set of candidate device positions associated with different insertion points, - a selection unit (11; 407) configured to determine, for each of at least some non-selected candidate device positions of the set, a sum of negative derivatives of the constraint function with respect to the treatment parameter associated with the respective device position and to select a device position for use in the treatment from the set of candidate device positions based on a comparison of the determined sums, and - an optimization unit (12; 408) configured to determine at least one optimized treatment parameter for the selected device position based on the constraint function, characterized in that the selection unit (11; 407) is configured to determine a sum of negative derivatives for each non-selected candidate device position of the set of candidate device positions and to select a device position based on a comparison of all determined sums. the devices (4a,b,c; 403a,b,c) being operated within the patient body in one or more device positions and in accordance with treatment parameters associated with the device positions, each device position being reached via an associated insertion point into the patient body, wherein the system comprises: - a constraint function generation unit (10; 406) configured to generate a constraint function representing clinical objectives relating to the treatment quantity, the constraint function depending upon at least one associated treatment parameter of each candidate device position of a set of candidate device positions associated with different insertion points, - a selection unit (11; 407) configured to determine, for each of at least some non-selected candidate device positions of the set, a sum of negative derivatives of the constraint function with respect to the treatment parameter associated with the respective device position and to select a device position for use in the treatment from the set of candidate device positions based on a comparison of the determined sums, and - an optimization unit (12; 408) configured to determine at least one optimized treatment parameter for the selected device position based on the constraint function, characterized in that the selection unit (11; 407) is configured to determine a sum of negative derivatives for each non-selected candidate device position of the set of candidate device positions and to select a device position based on a comparison of all determined sums. - a constraint function generation unit (10; 406) configured to generate a constraint function representing clinical objectives relating to the treatment quantity, the constraint function depending upon at least one associated treatment parameter of each candidate device position of a set of candidate device positions associated with different insertion points, - a selection unit (11; 407) configured to determine, for each of at least some non-selected candidate device positions of the set, a sum of negative derivatives of the constraint function with respect to the treatment parameter associated with the respective device position and to select a device position for use in the treatment from the set of candidate device positions based on a comparison of the determined sums, and - an optimization unit (12; 408) configured to determine at least one optimized treatment parameter for the selected device position based on the constraint function, characterized in that the selection unit (11; 407) is configured to determine a sum of negative derivatives for each non-selected candidate device position of the set of candidate device positions and to select a device position based on a comparison of all determined sums.