Abstract: Disclosed are methods for determining whether a patient will achieve a response after radiation therapy, in particular a method for determining whether a patient suffering from a cancer will achieve a response after radiation therapy including the steps of i) determining the level of ceramide in a first blood sample obtained from the patient before radiation therapy, ii) determining the level of ceramide in a second blood sample obtained from the patient during or just after radiation therapy, iii) comparing the level determined at step i) with the level determined at step ii) and iv) concluding that the patient will achieve response when the level determined at step ii) is higher than the level determined at step i) or concluding that the patient will not achieve a response when the level determined at step ii) is lower than the level determined at step i).