• Age ≥ 40 years, male.

• Patients with histologically-confirmed diagnosis of prostate adenocarcinoma.

• pathologically node-negative (pN0) or pathologically node cannot be assessed (pNx);

• Patients with PSA \< 0.1ng/ml within 8 weeks after radical prostatectomy (RP) and maintained for at least 6 months;

• Biochemical recurrence (two consecutive rises in PSA with absolute values \> 0.2ng/ml, the time interval ≥ 2 weeks apart ) and no local recurrence or distant metastatic lesions on conventional imaging (bone scan and CT/MRI scan);

• Eastern Cooperative Oncology Group (ECOG) performance status score of 0 to 1;

• Estimated life expectancy \>10 year;

• Adequate laboratory parameters

‣ Absolute Neutrophil Count (ANC) ≥ 1.5 x 10\^9/L

⁃ Platelet count (PLT) ≥ 100 x 10\^9/L

⁃ Haemoglobin (Hb) ≥ 90 g/L

⁃ Serum creatinine (Cr) ≤ 1.5 x upper limit of normal(ULN) or creatinine clearance \> 50 ml/min.

⁃ Total bilirubin (TBIL) ≤ 1.5 x ULN.

⁃ Glutamic oxaloacetic transaminase (AST/SGOT) or glutamic alanine transaminase (ALT/SGPT) levels ≤ 2.5 x ULN.

⁃ International normalised ratio (INR) ≤1.5, prothrombin time (PT) and activated partial thromboplastin time (APTT)≤1.5 x ULN .

⁃ Left ventricular ejection fraction (LVEF) ≥ 50%.

• Patients able to comply with the protocol. Arm 1 subjects are proposed to receive salvage radiation therapy, while arm 2 subjects are not suitable for or refuse radiation therapy.

⁃ Signed informed consent.