The purpose of this study is to select the best therapeutic strategy in studying the effectiveness of the association of a short duration hormonal therapy and radiotherapy compared with radiotherapy alone, in patients with a detectable PSA after radical prostatectomy.

Study the effectiveness of the association of a short duration hormonal therapy by degarelix (Firmagon ®) and radiotherapy, with radiotherapy alone on survival without events in the treatment of detectable PSA after radical prostatectomy. 122 patients should be included over a period of 2 years. Patients will be treated according to the following scheme: * Arm A (61 patients) : Pelvic Radiotherapy: 46 Gy and prostate only boost up to 66 Gy * Arm B (61 patients) : Arm A + hormonal therapy by degarelix during 6 months