The invention relates to a method for generating a radiation treatment plan and a radiation therapy treatment planning system for use in effecting radiation therapy of an anatomical portion of an animal body. The invention also relates to a radiation therapy delivery system. The present invention aims to provide a new method for generating a radiation treatment plan for use in effecting radiation therapy of an anatomical portion of a human and animal body, whereby a more efficient use can be made of the virtual working space of the treatment planning system and hence provide a more accurate match between the planned radiation dose distribution and the ideal radiation dose distribution profile position. This is achieved by defining a starting position and a finishing position along said trajectory for each of said catheters and by defining a dwell step corresponding to an equal number of dwell positions fitting the trajectory between said starting position and said finishing position and then determining the radiation dose distribution for each of said catheters based on said equal number of dwell positions.
