[Adjuvant radiotherapy in lymph-node-positive prostate cancer with low tumor burden after radical prostatectomy : Multicenter randomized phase III trial on the effect of adjuvant radio therapy in patients with prostate cancer with or without positive margins after radical prostatectomy (RP) and lymph node metastasis with low tumor burden (micrometastases, ≤ 2 lymph node macrometastases). ART-2 trial AP 61/11 of the AUO].