This study is the first prospective, randomized phase III clinical trial designed to evaluate whether ultrahypofractionated radiotherapy is non-inferior to conventionally moderately hypofractionated radiotherapy in terms of efficacy, with acceptable toxicity, in patients who develop biochemical recurrence following radical prostatectomy.

Considering the potential clinical benefits of shorter treatment duration, cost reduction, and improved patient convenience, this study is expected to provide important evidence to optimize salvage radiotherapy strategies in routine clinical practice.

Moderate hypofractionated radiotherapy (Moderate-hypoRT): 60 Gy in 24 fractions, delivered once daily, 5 days per week (on weekdays), over a total of 5-6 weeks.

Ultra-hypofractionated radiotherapy (Ultra-hypoRT): 31 Gy in 5 fractions, delivered every other day (2-3 fractions per week), over a total of 2 weeks.

Inclusion Criteria:

• Patients who have undergone radical prostatectomy for prostate cancer
• Age ≥ 20 years
• Persistent prostate-specific antigen (PSA) elevation after radical prostatectomy, defined as prostate-specific antigen (PSA) levels of 0.1-1.0 ng/mL with at least three consecutive increases
• Patients who have undergone prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT) for evaluation of prostate-specific antigen (PSA) elevation
• Good performance status (ECOG performance status 0-1)

Exclusion Criteria:

• Radiologic or clinical evidence of gross local recurrence, lymph node metastasis, or distant metastasis, including findings on prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA PET/CT), as determined by the treating physician
• Presence of lymph node metastasis or distant metastasis at the time of radical prostatectomy
• History of prior pelvic radiotherapy
• Diseases associated with a high risk of radiation toxicity (e.g., inflammatory bowel disease, systemic lupus erythematosus, scleroderma, or other connective tissue diseases)
• History of another malignancy diagnosed or recurrent within the past 3 years (except for skin cancer and thyroid cancer)
• Uncontrolled acute or chronic conditions deemed inappropriate for study participation by the investigator (e.g., dementia, Alzheimer's disease, cerebral infarction, etc.)