The goal of this clinical study is to determine impact of carbon ion radiotherapy (CIRT) treatment in combination with systemic therapy for oligo-metastatic prostate cancer. The primary objective: to determine disease biochemical progression-free survival in man with oligo-metastatic (M1a/b) prostate cancer undergoing systemic therapy with definitive radiotherapy of the primary tumor. The secondary objective: to determine local control, overall survival and quality of life in men with oligo-metastatic prostate cancer undergoing carbon ion radiotherapy