Background: We aimed to evaluate the long-term outcomes, treatment-related toxicity, and factors affecting postoperative prostate cancer patients treated with intensi-ty-modulated radiation therapy and image-guided radiation therapy (IMRT-IGRT) using TomoTherapy as salvage radiotherapy (SRT). Methods: We included 71 consecutive patients who underwent SRT after radical prostatectomy between 2011 and 2023. Treatment outcomes, including the progression-free rate (PFR) and overall survival, were calculated using Kaplan–Meier curves. Associations between treatment outcomes and factors were analyzed using the Cox proportional hazards regression analysis. Results: The median follow-up time after SRT was 60 (range, 1–148) months. The 5-year and 10-year PFR were 69.05% and 54.73%, respectively. In multivariate analysis, PSA maximum after surgery (mas PSA) >0.7 ng/mL was significantly associated with worse PFR (p 0.7 ng/mL, providing critical insights into prognostication. SRT for prostate cancer with IMRT and IGRT using TomoTherapy showed similar treatment outcomes and low toxicity rates compared with those of previous studies.