A system and method for optimizing fractionation schemes in planning radiation therapy are provided, as well as a computer program and a computer program product for carrying out the method, and an arrangement for planning radiation therapy. For optimizing the fractionation schemes, the following steps are performed. Anatomical image data of a subject to be treated is received by a biological impact calculation module as well as a predetermined radiation therapy treatment plan comprising a dose distribution to be delivered to the subject. A first set of reference parameters of a fractionation scheme is received, and also a second set of parameters of a fractionation scheme is received. Based on this, the module calculates the biological impact of the radiation therapy treatment. The calculated biological impact results are provided simultaneously for the first and the second sets of received parameters.
