[Adjuvant radiotherapy for lymph-node-positive prostate cancer with low tumor load after radical prostatectomy : Multicenter randomized phase III study of the effect of adjuvant radiotherapy in patients with prostate cancer with or without a positive margin after radical prostatectomy (RP) and lymph node metastasis with low tumor load (micrometastases, ≤ 2 lymph node macrometastases). ART-2 - study AP 61/10 of the AUO].