The invention relates to a method for calculating the radiation dose distribution for a radiation treatment system for the purpose of radiation therapy of an animal body, wherein said radiation beam of the radiation treatment system exhibits a specific beam field size and shape at different depths as well as to a device for calculating the radiation dose distribution for a radiation treatment system for the purpose of radiation therapy of an animal body, wherein said radiation beam of the radiation treatment system exhibits a specific beam field size and shape at different depths. It is an object of the invention to provide a method and device according to the above allowing the calculation of a radiation dose distribution for a radiation treatment system using a limited amount of data whilst preserving the required accuracy. According to the invention the method is characterized by the steps of i) determining at least one beam quality index being representative for said radiation beam being used, and ii) calculating said radiation dose distribution in said specific beam field using parameterized dose deposition kernels based on said at least one beam quality index.
